Introduction to physics

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- [Voiceover] I could imagine

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that even the earliest human beings,

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or possibly pre-human beings

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had asked themselves the questions,

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"Why am I here? What is the nature of reality?

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"Why is the universe organized the way that it is?"

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And these questions are what we attempt to answer

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in the field of physics...

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In the field of physics,

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which you could view

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maybe right after mathematics

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as the purest of the sciences.

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So you have math, which is very pure,

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and then on that foundation of math

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you have physics.

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And physics really does try to use that mathematics

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along with some core ideas

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to explain the phenomena,

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all the phenomena,

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of the universe.

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And physicists will the the first to admit

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that they are just beginning to understand

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the nature of reality,

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the nature of everything around us.

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Now a lot of times, we think physics

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is only limited to things like cosmological phenomena

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or getting rockets into space,

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or how waves move or building structures.

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But physics is the foundation for

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all of the other sciences.

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When we think about chemistry,

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when we think about chemistry,

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which is at the end of the day

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interactions between atoms,

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those interactions are really physics-based interactions.

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So chemistry, chemistry is actually laid down

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on a foundation of physics.

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And then even when we think about ourselves,

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our bodies, even our consciousness, our brains,

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it really all boils down to chemistry and physics.

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It boils down to interactions between atoms

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and even mechanical properties of our bodies.

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And so even biology,

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even what we are,

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is built on a foundation of chemistry.

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So this is biology right over here,

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which is built on a foundation of physics,

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which is highly dependent on some of the math

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that you've been learning your whole life

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and that you will continue to learn.

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And that fundamental question that you might have said,

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"Well you know, hey, why am I learning this math?"

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Well one, 'cause the math is beautiful,

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but also you will see that it starts to,

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in almost the most pure way,

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describe the structure of the universe.

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And we're going to see that more and more and more

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as we go into physics.

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All of this complex phenomena

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that you see around us,

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whether we're looking at a galaxy

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or we're looking at ocean waves,

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or we're looking at even biological systems,

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we'll see that a shocking amount of them

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can start to be described using some fairly elegant

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mathematics that we can build on

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and continue to build on.

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Simple or elegant mathematics

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like force is equal to mass times acceleration.

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And we're gonna talk about force and acceleration

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as vector quantities.

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We're gonna think about things like displacement,

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and I'll put it as a vector quantity,

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and we'll soon learn more about vector

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and scalar quantities are.

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Displacement is equal to velocity times time.

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We'll learn things like accelaration

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is equal to change in velocity over change in time.

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What we'll see with even a handful

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of very simple ideas like this.

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We'll go into much more depth in future videos.

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You can explain all sorts of complex phenomena.

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And the one thing that I always loved about physics,

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and I don't think it's always fully appreciated,

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sometimes as you start to learn physics,

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you'll see all these complicated formula,

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all of these kind of complicated problems,

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but it's super valuable to realize

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it's all coming from some of these basic ideas.

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Some of the things that I just mentioned,

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these ideas, we're gonna explore ideas of energy.

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We're going to explore Newton's laws.

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We're going to explain, we're gonna think about

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what are the the different types of forces out there,

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and why they might, why they might actually exist.

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At its essence, it's all about trying to

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explain the complexity of the universe,

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predict what is going to happen

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based on simple ideas.

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And that's what physics is all about.

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Now when we think of physics,

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it's been studied by humanity for a very, very long time.

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In fact, I'm sure we don't know

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who the first physicists were.

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But some of the,

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I guess you could say foundational thinkers

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in physics are these gentlemen that I have here.

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And this is just a...

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You could kind of say

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this is some of the most prominent thinkers in physics,

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but this is by no means a complete list.

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First and foremost, we'd wanna include Isaac Newton.

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Especially when you start to study physics,

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you're starting to understand the world

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as Newton understood it.

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He understood, "Hey, you know,

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"things don't fall to the ground

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"just 'cause they always fall to,

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"just 'cause that's the way the universe is.

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"That's a force that's acting on it,

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"and maybe that same force that's causing me

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"to be stuck to my chair right now

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"is what keeps Earth orbiting around the Sun

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"or the moon orbiting around the Earth."

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He developed Law of Gravitation,

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Newton's Laws, and we're going to study that

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as we delve into our basic physics.

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And what we'll see,

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even classical mechanics,

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the physics that Newton established,

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can explain a large range of phenomena

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with amazing precision.

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But as we get into the early 20th century,

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physics starts to get even more wild

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as we start to look at the scales

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of the super small,

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and we have Max Planck giving us quantum mechanics,

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and then we have Albert Einstein

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as we start thinking about super fast speeds,

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the speed of light, and we realize that's an absolute.

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That nothing can travel faster than the speed of light,

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which is this mind-boggling thing

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that we have these notions

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of general and special relativity,

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and we start realizing that the universe

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is in some ways more bizarre, and more mysterious,

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and more fascinating than we ever could have imagined.

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But all of the work, even to understand the modern physics

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of Max Planck and Albert Einstein,

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it's based on a lot of the core ideas

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that were given to us by Isaac Newton,

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even people before Isaac Newton.

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So as you go into your study of physics,

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and I'm kind of a physicist wannabe.

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I wanted to be a physicist.

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I imagined kind of,

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'cause it's all about, we all wonder,

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why are we here?

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What is the nature of reality?

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Why do things happen the way they are?

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And these are the questions that physics

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is attempting to answer.

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And so as you go into your study of physics,

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I wanna leave you with some quotes

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from these three gentlemen.

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So the first two are from Isaac Newton.

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"Truth is ever to be found in simplicity,

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"and not in the multiplicity and the confusion of things."

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And I really wanted to stress this,

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because a lot of times in your studies,

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you might be finding yourself memorizing formulas

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and vocabulary, but that's,

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if you're doing that, you're just at the very surface.

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But if you really start to think about it,

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really start to think about where these things come from,

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it'll come to simpler and simpler and more intuitive ideas.

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And then, you are getting closer to the truth.

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Now, I love this second quote from Isaac Newton.

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"I do not know what I may appear to...

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"I do not know what I may appear to the world,

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"but to myself, I seem to have been only like a boy

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"playing on the seashore,

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"and diverting myself in now and then

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"finding a smoother pebble

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"or prettier shell than ordinary,

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"whilst the great ocean of truth

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"lay all undiscovered before me."

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I like to imagine there's so much,

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we, even though we think we know so much,

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that we haven't even learned a small fraction

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of how the universe really is.

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And even a great thinker like Isaac Newton,

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he recognized this.

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He's like, "Hey, I'm just kind of dabbling

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"into the seashore and picking up a pebble there,

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"but there's this vast ocean

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"that I can't even begin to understand."

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You can even imagine alien civilizations

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that are thousands of years ahead of us

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technologically or scientifically

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or even millions of years,

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how they might perceive the reality,

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and they might see us as ants

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in that we are just beginning

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to scrape the surface of how the world works.

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This is from Max Planck.

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"When you change the way you look at things,

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"the things you look at change."

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And I find this to be pretty profound,

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because it is true.

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As you study physics,

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you will start to see, whoa,

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most of what we consider to be reality,

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our current understanding is based

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on these forces, but what are these forces?

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And even these things that we think are solid,

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when we go down to the atomic level,

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we see it's mostly empty space

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and it's really just the interaction of forces

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that make us think that something

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is solid or there or tangible is some way.

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And you realize these very tangible things

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aren't so tangible after all.

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At the end of the day, the whole world

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is just a mental model that we have.

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In some ways,

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it's an illusion

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that our mind creates so that we can operate inside of it.

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But we're just beginning to understand it.

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And last but not least,

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and there's actually a ton of great quotes

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from these folks and others,

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but especially Albert Einstein.

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"The most beautiful experience

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"we can have is the mysterious.

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"It is the fundamental emotion that stands

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"at the cradle of true art and true science."

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And I really want you to take this to heart

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as you study your physics.

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There will be times where we're going

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to be building our tool kits.

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What's a vector?

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What's a scalar?

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Going into some mathematics,

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proving some formulas.

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Those are the tool kits,

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but then we're gonna try to understand

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fundamental phenomena.

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How does the universe actually work?

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And if when we start to think about these,

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you don't get a few chills on your skin,

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a few goosebumps, and feel that the universe

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is more mysterious than you thought,

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then we're not studying physics

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the say that we should be studying physics.


The cytoskeleton

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- (Voiceover) When we first learn about cells,

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because of the visualizations that we often see in

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textbooks or even some of the micrographs we

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might see from microscopes,

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we kind of imagine cells as these little balloons of

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fluid with things floating around in them.

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So, this right over here,

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this is a fairly common textbook visualization

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of a cross section of the cell and we see

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all of these important parts.

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We see the nucleus.

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We see the endoplasmic reticulum.

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We see the Golgi apparatus.

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We see mitochondria here.

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And the way that this is drawn,

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it looks like they're just floating.

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It looks like they're just floating in the cytosol.

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And it is true that there is a lot of water in cells.

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In fact, you are mostly water and

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most of that water that makes up you is found in cells.

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But it turns out that these types of drawings

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are missing a very crucial aspect of the structure of cells.

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They are missing the cytoskeleton.

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Cyto, cytoskeleton.

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And this is still something that we are trying to

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understand better of what, how does the

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cytoskeleton work and how does it help

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the cell have its structure and move things around

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and give it its shape.

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So cytoskeleton-it's one word,

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but I've written the different parts of the words,

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the different parts of the word,

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in different colors here because this literally means

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"cell skeleton".

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So if I were to actually try to visualize

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this cytoskeleton here,

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I have all sorts of these structures.

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I'll use a different color.

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I have all sorts of these structures criss-crossing the cell

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in different ways that have proteins

00:01:26.029 --> 00:01:27.817
bound to them and they're even moving

00:01:27.817 --> 00:01:29.559
and they're growing and they can

00:01:29.559 --> 00:01:30.998
help the cell move around or they can help

00:01:30.998 --> 00:01:32.972
transport things within the cell and

00:01:32.972 --> 00:01:34.829
other things could be lodged in them.

00:01:34.829 --> 00:01:37.453
And so it's a much, much, much, much more

00:01:37.453 --> 00:01:39.769
complex thing that we're talking about than what

00:01:39.769 --> 00:01:42.509
was depicted in this visualization before

00:01:42.509 --> 00:01:45.063
I had my chance to scribble on it.

00:01:45.063 --> 00:01:46.387
And to help us visualize it,

00:01:46.387 --> 00:01:47.942
I've found this picture.

00:01:47.942 --> 00:01:49.173
It's a public domain picture.

00:01:49.173 --> 00:01:50.543
And I found it fascinating cause it really helps

00:01:50.543 --> 00:01:53.329
you think about the complexity that is going on

00:01:53.329 --> 00:01:55.930
in even one of your cells.

00:01:55.930 --> 00:01:59.273
So, let's look at some of the structures over here.

00:01:59.273 --> 00:02:04.407
So, this thing that I'm kind of tracing right over here,

00:02:08.027 --> 00:02:09.861
this is called a microfilament.

00:02:09.861 --> 00:02:12.392
This is a microfilament.

00:02:12.392 --> 00:02:13.669
Let me write that.

00:02:13.669 --> 00:02:17.477
That's a microfilament.

00:02:19.027 --> 00:02:20.556
And just to get a sense of the scale,

00:02:20.556 --> 00:02:23.781
its diameter, so this diameter is

00:02:23.781 --> 00:02:25.801
gonna be about six or seven nanometers.

00:02:25.801 --> 00:02:29.678
So, approximately six to seven nanometers,

00:02:29.678 --> 00:02:32.604
six to seven billionths of a meter.

00:02:32.604 --> 00:02:34.090
And to have, to just get a sense of that relative

00:02:34.090 --> 00:02:35.994
to the cell itself,

00:02:35.994 --> 00:02:41.079
a typical cell could be six to seven micrometers

00:02:41.079 --> 00:02:42.936
in diameter or larger.

00:02:42.936 --> 00:02:45.374
So this is essentially one thousandth of

00:02:45.374 --> 00:02:47.580
the diameter of the cell.

00:02:47.580 --> 00:02:50.320
So these things that I am drawing right over here,

00:02:50.320 --> 00:02:53.176
these actually would not be that far off in terms of scale.

00:02:53.176 --> 00:02:54.639
In fact, I'd probably want to draw it even thinner.

00:02:54.639 --> 00:02:55.869
And that's why you often won't see it in

00:02:55.869 --> 00:02:59.167
these diagrams cause you would have to draw it so thin.

00:02:59.167 --> 00:03:01.860
The diameter of one of these filaments is roughly,

00:03:01.860 --> 00:03:03.091
order of magnitude,

00:03:03.091 --> 00:03:08.176
a thousandth of the diameter of a fairly typical cell.

00:03:08.176 --> 00:03:09.662
But these things are incredibly important.

00:03:09.662 --> 00:03:11.732
They help give the structure of the cell.

00:03:11.732 --> 00:03:15.222
They're made up of actin proteins.

00:03:15.222 --> 00:03:16.197
So you can see,

00:03:16.197 --> 00:03:17.706
there's kind of these two actin,

00:03:17.706 --> 00:03:20.609
you could kind of visualize them as ropes,

00:03:20.609 --> 00:03:22.188
wrapped around each other.

00:03:22.188 --> 00:03:24.881
And so this, the protein involved here.

00:03:24.881 --> 00:03:25.833
Let me do this.

00:03:25.833 --> 00:03:27.551
I'm using that color too much.

00:03:27.551 --> 00:03:31.127
The protein involved in these microfilaments is actin.

00:03:31.127 --> 00:03:34.447
This is actin.

00:03:34.447 --> 00:03:35.910
And what's neat about these microfilaments

00:03:35.910 --> 00:03:37.071
in a cell, as I said,

00:03:37.071 --> 00:03:38.139
they help give structure.

00:03:38.139 --> 00:03:39.161
They help do all sorts of things.

00:03:39.161 --> 00:03:41.738
They can actually be dynamically kind of

00:03:41.738 --> 00:03:43.294
destroyed and created.

00:03:43.294 --> 00:03:44.548
Their lengths can be changed.

00:03:44.548 --> 00:03:48.170
This can help a cell actually move and even more,

00:03:48.170 --> 00:03:49.702
you can use them.

00:03:49.702 --> 00:03:51.235
You can transport things along them.

00:03:51.235 --> 00:03:52.674
You can pull and tug on them.

00:03:52.674 --> 00:03:54.369
And there's actually a fascinating interaction

00:03:54.369 --> 00:03:57.690
between actin and what you see over here.

00:03:57.690 --> 00:04:00.197
This right over here,

00:04:00.197 --> 00:04:01.962
this is made up of myosin.

00:04:01.962 --> 00:04:03.239
This is myosin.

00:04:03.239 --> 00:04:05.166
My-let me write this.

00:04:05.166 --> 00:04:06.397
It's hard to see.

00:04:06.397 --> 00:04:07.743
That is myosin.

00:04:07.743 --> 00:04:09.020
Myosin.

00:04:09.020 --> 00:04:10.785
And the relationship with actin, myosin can

00:04:10.785 --> 00:04:14.570
act as kind of this thing that kicks along the myosin.

00:04:14.570 --> 00:04:16.497
And they can move relative to each other.

00:04:16.497 --> 00:04:18.981
And this is essential for muscles contracting.

00:04:18.981 --> 00:04:22.116
It's fascinating to see that even things like proteins,

00:04:22.116 --> 00:04:23.950
which are just made up of a bunch of amino acids,

00:04:23.950 --> 00:04:26.690
they can interact in these fairly complex ways

00:04:26.690 --> 00:04:29.778
that you can have these myosin things kick along

00:04:29.778 --> 00:04:33.609
and move and tug on the actin.

00:04:33.609 --> 00:04:35.746
So that's myosin right over there.

00:04:35.746 --> 00:04:38.369
We see ribosomes.

00:04:38.369 --> 00:04:40.064
These ribosomes are the ribosomes that

00:04:40.064 --> 00:04:41.597
are not attached to the endoplasmic reticulum.

00:04:41.597 --> 00:04:44.244
So these are free ribosomes around here.

00:04:44.244 --> 00:04:46.751
So you can see it's incredibly, incredibly complex.

00:04:46.751 --> 00:04:47.657
You might say ok,

00:04:47.657 --> 00:04:52.370
I see these microfilaments made up of actin.

00:04:52.370 --> 00:04:54.599
I see one, the one I outlined.

00:04:54.599 --> 00:04:55.900
There's others over here.

00:04:55.900 --> 00:04:58.477
I see another one right over here.

00:04:58.477 --> 00:05:00.520
I see one up over here.

00:05:00.520 --> 00:05:04.351
But what are these big tube-like structures

00:05:04.351 --> 00:05:06.000
that we also see?

00:05:06.000 --> 00:05:07.138
So for example,

00:05:07.138 --> 00:05:08.322
what is this,

00:05:08.322 --> 00:05:10.388
what are these tube-like structures?

00:05:10.388 --> 00:05:13.844
Well these are called microtubules.

00:05:14.644 --> 00:05:18.112
So, micro, microtubules.

00:05:19.142 --> 00:05:21.562
And they look massive compared to the microfilaments,

00:05:21.562 --> 00:05:24.929
but they're still fairly small on the cellular scale.

00:05:24.929 --> 00:05:26.902
This is about 25 nanometers.

00:05:29.182 --> 00:05:31.948
And once again these play a huge role

00:05:31.948 --> 00:05:33.120
in the structure of cells.

00:05:33.120 --> 00:05:34.676
And they allow things to be organized and

00:05:34.676 --> 00:05:35.790
things to be transported.

00:05:35.790 --> 00:05:37.810
And these are also dynamic pieces of the cell.

00:05:37.810 --> 00:05:40.039
And they can be constructed and they can be destroyed.

00:05:40.039 --> 00:05:43.383
And they can change the shape of the actual cells.

00:05:43.383 --> 00:05:44.404
And in animal cells,

00:05:44.404 --> 00:05:46.215
the things I've just described are found in most cells,

00:05:46.215 --> 00:05:47.446
but in animal cells,

00:05:47.446 --> 00:05:49.907
you will also find things called intermediate filaments

00:05:49.907 --> 00:05:52.067
that are actually in between these two in size

00:05:52.067 --> 00:05:55.410
which also help maintain shape and do other things.

00:05:55.410 --> 00:05:57.871
So the whole point of this video is to

00:05:57.871 --> 00:05:59.636
just give you even more appreciation.

00:05:59.636 --> 00:06:01.470
Hopefully all the other videos we've had on cells

00:06:01.470 --> 00:06:03.537
have given you appreciation for how much beauty

00:06:03.537 --> 00:06:05.859
and how much complexity there are

00:06:05.859 --> 00:06:07.600
in things that a lot of times on an everyday level,

00:06:07.600 --> 00:06:09.527
we think of as something as simple as a cell.

00:06:09.527 --> 00:06:11.896
But there's all this beauty and complexity to its

00:06:11.896 --> 00:06:13.893
structure that's often not even depicted

00:06:13.893 --> 00:06:15.843
in the drawings of the cells that

00:06:15.843 --> 00:06:18.072
you might find in your textbooks.

00:06:18.072 --> 00:06:19.860
And to get a better appreciation,

00:06:19.860 --> 00:06:21.183
here are some public domain images

00:06:21.183 --> 00:06:23.180
I found of cells where you can see the

00:06:23.180 --> 00:06:25.525
cytoskeleton actually colored in.

00:06:25.525 --> 00:06:28.056
And what you see in this picture in particular,

00:06:28.056 --> 00:06:29.728
in this yellowish-green color,

00:06:29.728 --> 00:06:32.328
this is actually cow lung cells right over here,

00:06:32.328 --> 00:06:33.629
this yellowish-green structure,

00:06:33.629 --> 00:06:35.904
these yellowish-green lines you see,

00:06:35.904 --> 00:06:37.413
those are the microtubules.

00:06:37.413 --> 00:06:40.060
And what you see in this pinkish or orangish color,

00:06:40.060 --> 00:06:41.988
these are the microfilaments.

00:06:41.988 --> 00:06:44.356
So you get a appreciation for how complex and

00:06:44.356 --> 00:06:47.676
structured these things that you used to think

00:06:47.676 --> 00:06:50.759
were just big blobs actually are.


Mitochondria

WEBVTT
Kind: captions
Language: en

00:00:00.350 --> 00:00:03.720
- Let's delve into the world of mitochondria

00:00:03.720 --> 00:00:07.250
which are probably my favorite organelle.

00:00:07.250 --> 00:00:10.090
So let's just have a little review of what mitochondria are

00:00:10.090 --> 00:00:11.450
and then we can delve a little bit deeper

00:00:11.450 --> 00:00:13.390
into their structure.

00:00:13.390 --> 00:00:15.990
So let's just think about a cell

00:00:15.990 --> 00:00:18.490
and not just any cell, but a eukaryotic cell.

00:00:18.490 --> 00:00:20.120
So that's the cellular membrane

00:00:20.120 --> 00:00:23.650
and when people say a eukaryote or a eukaryotic cell

00:00:23.650 --> 00:00:27.290
they most typically say, "Oh! That must have its nuclear DNA

00:00:27.290 --> 00:00:31.020
"in a membrane-bound nucleus." and that would be true,

00:00:31.020 --> 00:00:33.690
so let's draw our membrane-bound nucleus.

00:00:33.690 --> 00:00:35.220
That's our nuclear membrane.

00:00:35.220 --> 00:00:38.090
You have your DNA in here,

00:00:38.090 --> 00:00:39.990
so let's draw some DNA.

00:00:39.990 --> 00:00:42.190
But when we talk about eukaryotic cells,

00:00:42.190 --> 00:00:44.990
we're not just talking about a membrane-bound nucleus,

00:00:44.990 --> 00:00:47.720
we're also talking about other membrane-bound organelles

00:00:47.720 --> 00:00:51.180
and in a close second place for a membrane-bound structure

00:00:51.180 --> 00:00:52.720
that is very important to the cell

00:00:52.720 --> 00:00:55.550
would be the mitochondria.

00:00:55.550 --> 00:00:58.890
So let's draw some mitochondria right over here.

00:00:58.890 --> 00:01:00.120
So I'll talk a little bit more about

00:01:00.120 --> 00:01:02.020
what these little squiggly lines that I'm drawing

00:01:02.020 --> 00:01:04.120
inside of the mitochondria are

00:01:04.120 --> 00:01:05.290
and this is actually a little bit more

00:01:05.290 --> 00:01:06.920
of a textbook visualization, as we'll learn

00:01:06.920 --> 00:01:09.450
in a few minutes or seconds that we now have more

00:01:09.450 --> 00:01:12.050
sophisticated visualizations of what's actually going on

00:01:12.050 --> 00:01:13.690
inside of a mitochondria, but we haven't actually

00:01:13.690 --> 00:01:15.250
answered all of our questions,

00:01:15.250 --> 00:01:17.150
but you might have already learned that,

00:01:17.150 --> 00:01:20.090
so let me make it clear, these are mitochondria.

00:01:20.090 --> 00:01:21.020
That's the plural.

00:01:21.020 --> 00:01:22.050
If we're just talking about one of them,

00:01:22.050 --> 00:01:24.220
we're talking about a mitochondrion.

00:01:24.220 --> 00:01:26.120
That's the singular of mitochondria.

00:01:26.120 --> 00:01:27.720
But you might have already learned,

00:01:27.720 --> 00:01:31.190
some time in your past or in another Khan Academy video,

00:01:31.190 --> 00:01:35.960
that these are viewed as the ATP factories for cells.

00:01:35.960 --> 00:01:38.750
So let me right it this way.

00:01:38.750 --> 00:01:40.990
So ATP factories.

00:01:40.990 --> 00:01:45.720
A-T-P factories and if you watched the videos on ATP

00:01:45.720 --> 00:01:48.050
or cellular respiration or other videos,

00:01:48.050 --> 00:01:51.720
I'd repeatedly talk about how ATP is really the currency

00:01:51.720 --> 00:01:55.090
for energy in the cell that when it's in its ATP form

00:01:55.090 --> 00:01:57.150
you have adenosine triphosphate.

00:01:57.150 --> 00:02:00.150
If you pop one of the phosphate groups off,

00:02:00.150 --> 00:02:02.920
you pop one of the P's off, it release energy

00:02:02.920 --> 00:02:05.320
and that's what your body uses to do all sort of things

00:02:05.320 --> 00:02:08.420
from movement to thinking to all sorts of things

00:02:08.420 --> 00:02:10.450
that actually go on in your bodies,

00:02:10.450 --> 00:02:12.850
so you can imagine mitochondria are really important

00:02:12.850 --> 00:02:16.450
for energy, for when the cell has to do things.

00:02:16.450 --> 00:02:18.760
And that's why you'll find more mitochondria

00:02:18.760 --> 00:02:21.210
in things like muscle cells, things that have to use

00:02:21.210 --> 00:02:22.950
a lot of energy.

00:02:22.950 --> 00:02:25.990
Now before I get into the structure of mitochondria,

00:02:25.990 --> 00:02:28.590
I wanna talk a little bit about its fascinating past

00:02:28.590 --> 00:02:31.550
because we think of cells as the most basic unit of life

00:02:31.550 --> 00:02:33.850
and that is true, that comes straight out of cell theory,

00:02:33.850 --> 00:02:36.450
but it turns out the most prevalent theory

00:02:36.450 --> 00:02:39.620
of how mitochondria got into our cells

00:02:39.620 --> 00:02:43.390
is that at one time the predecessors,

00:02:43.390 --> 00:02:45.220
the ancestors to our mitochondria,

00:02:45.220 --> 00:02:49.790
were free, independent organisms, microorganisms.

00:02:49.790 --> 00:02:54.320
So they're descendent from bacterial-like microorganisms

00:02:54.320 --> 00:02:57.550
that might have been living on their own

00:02:57.550 --> 00:02:59.650
and they were maybe really good at processing energy

00:02:59.650 --> 00:03:01.290
or maybe they were even good at other things,

00:03:01.290 --> 00:03:04.190
but at some point in the evolutionary past,

00:03:04.190 --> 00:03:08.050
they got ingested by what the ancestors of our cells

00:03:08.050 --> 00:03:10.510
and instead of just being engulfed and being torn to shreds

00:03:10.510 --> 00:03:12.450
and kind of being digested and eaten,

00:03:12.450 --> 00:03:15.250
it was like, "Hey, wait, if these things stick around,

00:03:15.250 --> 00:03:17.120
"those cells are more likely to survive

00:03:17.120 --> 00:03:19.850
"because they're able to help process glucose

00:03:19.850 --> 00:03:24.550
"or help generate more energy out of things."

00:03:24.550 --> 00:03:27.920
And so the cells that were able to kind of live

00:03:27.920 --> 00:03:30.320
in symbiosis have them kind of give a place

00:03:30.320 --> 00:03:33.190
for the mitochondria to live or the pre-mitochondria,

00:03:33.190 --> 00:03:35.490
the ancestor mitochondria, those survived

00:03:35.490 --> 00:03:38.990
and then through kind of the processes of natural selection,

00:03:38.990 --> 00:03:41.350
this is what we now associate,

00:03:41.350 --> 00:03:43.290
we now associate eukaryotic cells

00:03:43.290 --> 00:03:44.890
as having mitochondria,

00:03:44.890 --> 00:03:47.820
so I find this whole idea of one organism being inside

00:03:47.820 --> 00:03:52.090
of another organism in symbiosis even at the cellular level,

00:03:52.090 --> 00:03:55.350
that's kind of mind-boggling, but anyway,

00:03:55.350 --> 00:03:57.590
I'll stop talking about that and now let's just talk

00:03:57.590 --> 00:03:59.850
about the present, let's talk about

00:03:59.850 --> 00:04:03.220
what the actual structure of mitochondria are.

00:04:03.220 --> 00:04:06.120
And I'll first draw kind of a simplified drawing

00:04:06.120 --> 00:04:10.050
of a mitochondion and I'll draw a cross section.

00:04:10.050 --> 00:04:13.120
So, I'm gonna draw a cross section.

00:04:13.120 --> 00:04:15.590
So if we were to kind of cut it in half.

00:04:15.590 --> 00:04:16.990
So what I've drawn right over here

00:04:16.990 --> 00:04:18.720
this would be its outer membrane.

00:04:18.720 --> 00:04:24.190
This is the outer membrane right over here

00:04:24.190 --> 00:04:25.520
and we label that.

00:04:25.520 --> 00:04:28.390
Outer membrane.

00:04:28.390 --> 00:04:30.588
And all of these membranes that I'm gonna draw,

00:04:30.588 --> 00:04:34.250
they're all going to be phospholipid bilayers.

00:04:34.250 --> 00:04:38.550
So if I were to zoom in right over here,

00:04:38.550 --> 00:04:41.420
so let me, if I were to zoom in,

00:04:41.420 --> 00:04:44.390
we would see a bilayer of phospholipids.

00:04:44.390 --> 00:04:47.350
So you have your

00:04:47.350 --> 00:04:50.490
hydrophilic heads facing outwards,

00:04:50.490 --> 00:04:53.390
hydrophilic heads facing outwards

00:04:53.390 --> 00:04:57.050
and your hydrophobic tails facing inwards.

00:04:57.050 --> 00:04:59.200
So.

00:05:00.090 --> 00:05:02.250
You see something just like that,

00:05:02.250 --> 00:05:05.880
so they're all phospholipid bilayers.

00:05:05.880 --> 00:05:07.890
But they aren't just phospholipids.

00:05:07.890 --> 00:05:10.220
All of these membranes have all sorts of proteins imbedded,

00:05:10.220 --> 00:05:13.250
I mean cells are incredibly complex structures,

00:05:13.250 --> 00:05:16.890
but even organelles like mitochondria have a fascinating,

00:05:16.890 --> 00:05:18.690
I guess you would say sub-structure to them.

00:05:18.690 --> 00:05:21.120
They themselves have all sorts of interesting proteins,

00:05:21.120 --> 00:05:23.150
enzymes imbedded in their membranes

00:05:23.150 --> 00:05:25.450
and are able to help regulate what's going on

00:05:25.450 --> 00:05:28.490
inside and outside of these organelles.

00:05:28.490 --> 00:05:34.760
And one of the proteins that you have in the outer membrane

00:05:34.760 --> 00:05:38.612
of mitochondria, they're called porins

00:05:38.612 --> 00:05:40.390
and porins aren't found only in mitochondria,

00:05:40.390 --> 00:05:41.590
but they're kind of tunnel proteins,

00:05:41.590 --> 00:05:44.450
they're structured so they kind of form a hole

00:05:44.450 --> 00:05:46.550
in the outer membrane.

00:05:46.550 --> 00:05:49.350
So I'm drawing them the best that I can.

00:05:49.350 --> 00:05:51.080
These are porins

00:05:51.080 --> 00:05:54.320
and what's interesting about porins is they don't allow

00:05:54.320 --> 00:05:57.120
large molecules to pass through passively,

00:05:57.120 --> 00:06:02.050
but small molecules like sugars or ions can pass passively

00:06:02.050 --> 00:06:04.090
through the porins.

00:06:04.090 --> 00:06:06.120
And so, because of that, your ion concentration

00:06:06.120 --> 00:06:07.450
and well, I should actually say,

00:06:07.450 --> 00:06:09.085
your small molecule concentrations tend

00:06:09.085 --> 00:06:12.555
to be similar on either side of this membrane,

00:06:12.555 --> 00:06:15.085
on either side of this outer membrane.

00:06:15.085 --> 00:06:17.125
But that's not the only membrane involved

00:06:17.125 --> 00:06:18.845
in a mitochondrion.

00:06:18.845 --> 00:06:20.685
We also have a inner membrane.

00:06:20.685 --> 00:06:22.605
I'll do that in yellow.

00:06:22.955 --> 00:06:24.155
We also have a inner membrane

00:06:24.155 --> 00:06:27.285
and I'm gonna draw it with a textbook model first

00:06:27.285 --> 00:06:28.545
and then we'll talk a little bit about,

00:06:28.545 --> 00:06:32.885
since we think this model is not quite right,

00:06:32.885 --> 00:06:36.685
but in this, so we have this inner membrane,

00:06:36.685 --> 00:06:41.625
inner membrane,

00:06:41.625 --> 00:06:45.525
and this inner membrane has these folds in it

00:06:45.525 --> 00:06:46.985
to increase their surface area

00:06:46.985 --> 00:06:48.555
and the surface area is really important

00:06:48.555 --> 00:06:50.485
for the inner membrane because that's

00:06:50.485 --> 00:06:53.355
where the processes of the electron transport chain

00:06:53.355 --> 00:06:55.955
occur across, essentially, these membranes.

00:06:55.955 --> 00:06:57.385
So you want this extra surface area

00:06:57.385 --> 00:07:00.685
so you can essentially have more of that going on.

00:07:00.685 --> 00:07:02.585
And these folds have a name.

00:07:02.585 --> 00:07:04.225
So if you're talking about one of them,

00:07:04.225 --> 00:07:05.725
if you're talking about one of these folds,

00:07:05.725 --> 00:07:10.005
you're talking about a crista,

00:07:10.005 --> 00:07:14.485
but if you're talking about more than one of them,

00:07:14.485 --> 00:07:18.555
you would call that a cristae, cristae.

00:07:18.555 --> 00:07:20.085
Sometimes I've seen the pronunciation of this

00:07:20.085 --> 00:07:24.525
as cristae, cristae or cristae, that's plural for crista.

00:07:24.525 --> 00:07:27.925
These are just folds in the inner membrane

00:07:27.925 --> 00:07:30.125
and once again the inner membrane is also

00:07:30.125 --> 00:07:33.655
a phospholipid bilayer.

00:07:33.655 --> 00:07:36.085
Now inside of the inner membranes,

00:07:36.085 --> 00:07:40.085
so between the outer membrane and the inner membrane

00:07:40.085 --> 00:07:42.985
you could imagine what this is gonna be called.

00:07:42.985 --> 00:07:46.485
That space is called the intermembrane space,

00:07:46.485 --> 00:07:51.885
not too creative of a name, intermembrane space

00:07:51.885 --> 00:07:53.885
and because of the porins,

00:07:53.885 --> 00:07:56.545
the small molecule concentration

00:07:56.545 --> 00:07:58.985
of the intermembrane space and then outside

00:07:58.985 --> 00:08:02.685
of the mitochondria,

00:08:02.685 --> 00:08:03.855
out in the cytosol,

00:08:03.855 --> 00:08:05.825
those concentrations are gonna be similar,

00:08:05.825 --> 00:08:08.585
but then the inner membrane does not have the porins

00:08:08.585 --> 00:08:11.425
in it and so you can actually have a different concentration

00:08:11.425 --> 00:08:12.655
on either side and that is essential

00:08:12.655 --> 00:08:14.625
for the electron transport chain.

00:08:14.625 --> 00:08:16.555
The electron transport chain really culminates

00:08:16.555 --> 00:08:19.055
with hydrogen, a hydrogen ion gradient

00:08:19.055 --> 00:08:20.785
being built between the two sides

00:08:20.785 --> 00:08:24.085
and then they flow down that gradient through a protein

00:08:24.085 --> 00:08:28.125
called ATP synthase which helps us synthesize ATP,

00:08:28.125 --> 00:08:29.925
but we'll talk more about that maybe in this video

00:08:29.925 --> 00:08:31.255
or in a future video,

00:08:31.255 --> 00:08:33.255
but let's finish talking about the different parts

00:08:33.255 --> 00:08:36.555
of a mitochondrion.

00:08:36.555 --> 00:08:40.125
So inside the inner membrane you have

00:08:40.125 --> 00:08:42.855
this area right over here is called the matrix.

00:08:42.855 --> 00:08:45.685
It's called, let me use this in a different color,

00:08:45.685 --> 00:08:47.875
this is

00:08:48.555 --> 00:08:49.385
the matrix

00:08:49.385 --> 00:08:50.955
and it's called the matrix 'cause it actually has

00:08:50.955 --> 00:08:53.225
a much higher protein concentration,

00:08:53.225 --> 00:08:58.085
it's actually more viscous than the cytosol

00:08:58.085 --> 00:09:02.185
that would be outside of the

00:09:03.675 --> 00:09:05.385
mitochondria.

00:09:05.385 --> 00:09:07.525
So this right over here is the matrix.

00:09:07.525 --> 00:09:09.815
When we we talk about cellular respiration,

00:09:09.815 --> 00:09:11.925
cellular respiration has many phases in it.

00:09:11.925 --> 00:09:13.345
We talk about glycolysis.

00:09:13.345 --> 00:09:15.955
Glycolysis is actually occurring in the cytosol.

00:09:15.955 --> 00:09:20.315
So glycolysis can occur in the cytosol.

00:09:20.315 --> 00:09:22.855
Glycolysis.

00:09:22.855 --> 00:09:26.025
But the other major phases of cellular respiration.

00:09:26.025 --> 00:09:28.055
Remember we talk about the citric acid cycle

00:09:28.055 --> 00:09:29.855
also known as the Krebs cycle,

00:09:29.855 --> 00:09:32.585
that is occuring in the matrix.

00:09:32.585 --> 00:09:35.825
So Krebs cycle

00:09:35.825 --> 00:09:37.225
is occuring in the matrix

00:09:37.225 --> 00:09:40.525
and then I said the electron transport chain

00:09:40.525 --> 00:09:42.155
which is really what's responsible for producing

00:09:42.155 --> 00:09:46.185
the bulk of the ATP, that is happening through proteins

00:09:46.185 --> 00:09:49.255
that are straddling the inner membrane

00:09:49.255 --> 00:09:55.125
or straddling the cristae right over here.

00:09:55.125 --> 00:09:56.855
Now we're just done.

00:09:56.855 --> 00:09:59.085
Probably one of the most fascinating parts of mitochondria,

00:09:59.085 --> 00:10:01.985
we said that we think that they are descendent

00:10:01.985 --> 00:10:04.725
from these ancient independent lifeforms

00:10:04.725 --> 00:10:06.825
and in order to be an ancient independent life form,

00:10:06.825 --> 00:10:09.055
they'd would have to have some information,

00:10:09.055 --> 00:10:13.655
some way to actually transmit their genetic information

00:10:13.655 --> 00:10:16.185
and, it turns out, mitochondria actually have

00:10:16.185 --> 00:10:18.085
their own genetic information.

00:10:18.085 --> 00:10:19.785
They have mitochondrial DNA

00:10:19.785 --> 00:10:21.785
and they often don't just even have one copy of it,

00:10:21.785 --> 00:10:23.415
they have multiple copies of it

00:10:23.415 --> 00:10:28.225
and they're in loops very similar to bacterial DNA.

00:10:28.225 --> 00:10:29.585
In fact, they have a lot in common

00:10:29.585 --> 00:10:30.855
with bacterial DNA and that's why we think

00:10:30.855 --> 00:10:34.385
that the ancestor to mitochondria that live independently

00:10:34.385 --> 00:10:38.655
was probably a form of bacteria or related to bacteria

00:10:38.655 --> 00:10:39.985
in some way.

00:10:39.985 --> 00:10:41.485
So this is, this right over there,

00:10:41.485 --> 00:10:43.885
that is the loop of mitochondrial DNA.

00:10:43.885 --> 00:10:46.555
So all the DNA that's inside of you, the bulk of it,

00:10:46.555 --> 00:10:50.385
yes, it is in your nuclear DNA, but you still have

00:10:50.385 --> 00:10:52.625
a little bit of DNA in your mitochondria

00:10:52.625 --> 00:10:55.615
and what's interesting is your mitochondrial DNA,

00:10:55.615 --> 00:10:59.455
your mitochondria, are inherited, essentially,

00:10:59.455 --> 00:11:03.275
from your mother's side, because when a egg is fertilized,

00:11:05.545 --> 00:11:08.825
a human egg has tons of mitochondria in it

00:11:09.615 --> 00:11:11.785
and I'm obviously not drawing all of the things

00:11:11.785 --> 00:11:12.825
in the human egg.

00:11:12.825 --> 00:11:14.285
It obviously has a nucleus and all of that.

00:11:14.285 --> 00:11:16.355
The sperm has some mitochondria in it,

00:11:17.985 --> 00:11:20.467
you could imagine it needs to be able

00:11:20.467 --> 00:11:22.325
to win that very competitive fight

00:11:22.325 --> 00:11:24.125
to get to fertilize the egg,

00:11:24.125 --> 00:11:26.355
but the current theory is all or most of that

00:11:26.355 --> 00:11:30.085
gets digested or dissolved once it actually gets

00:11:30.085 --> 00:11:31.525
into the egg.

00:11:31.525 --> 00:11:34.485
And anyway, the egg itself has way more mitochondria,

00:11:34.485 --> 00:11:38.755
so the DNA in your mitochondria is

00:11:38.755 --> 00:11:42.085
from your mother or is essentially from your mother's side

00:11:42.085 --> 00:11:43.655
and that's actually used, mitochondrial DNA,

00:11:43.655 --> 00:11:45.585
when people talk about kind of an ancient Eve

00:11:45.585 --> 00:11:47.425
or tracing back to having kind

00:11:47.425 --> 00:11:48.625
of one common mother,

00:11:48.625 --> 00:11:52.885
people are looking at the mitochondrial DNA,

00:11:52.885 --> 00:11:56.785
so it is actually quite, quite fascinating.

00:11:56.785 --> 00:11:58.725
Now I said a little bit earlier,

00:11:58.725 --> 00:12:00.855
and you know, obviously, it has its own DNA

00:12:00.855 --> 00:12:02.345
and then because it has its own DNA

00:12:02.345 --> 00:12:04.455
it's able to synthesize some of its own RNA,

00:12:04.455 --> 00:12:07.555
its own ribosomes, so it also has ribosomes here.

00:12:07.555 --> 00:12:10.455
But it doesn't synthesize all of the proteins

00:12:10.455 --> 00:12:11.725
that are sitting in mitochondria.

00:12:11.725 --> 00:12:14.385
A lot of those are still synthesized by

00:12:14.385 --> 00:12:17.455
or encoded for by your nuclear DNA

00:12:17.455 --> 00:12:19.955
and are actually synthesized outside of the mitochondria

00:12:19.955 --> 00:12:22.885
and then make their way into the mitochondria,

00:12:22.885 --> 00:12:25.855
but mitochondria are these fascinating, fascinating things.

00:12:25.855 --> 00:12:29.455
They're these little creatures living in symbiosis

00:12:29.455 --> 00:12:32.355
in our cells and they're able to replicate themselves

00:12:32.355 --> 00:12:34.685
and I don't know, I find all of this mind boggling.

00:12:34.685 --> 00:12:35.385
But anyway.

00:12:35.385 --> 00:12:37.785
I said that this was the textbook model

00:12:37.785 --> 00:12:39.725
because it turns out, when you look

00:12:39.725 --> 00:12:43.685
at a micrograph, a picture of mitochondria,

00:12:43.685 --> 00:12:45.485
it seems to back up this textbook model

00:12:45.485 --> 00:12:49.125
of these folds, these cristae just kind of folding in,

00:12:49.125 --> 00:12:51.755
but when we've been able to have more sophisticated

00:12:51.755 --> 00:12:53.645
visualizations it actually turns out

00:12:53.645 --> 00:12:55.985
that it's not just these simple folds

00:12:55.985 --> 00:12:59.055
that the inner membrane essentially hooks

00:12:59.055 --> 00:13:02.255
into the matrix and it turns out it has

00:13:02.255 --> 00:13:05.085
these little tunnels that connect the space

00:13:05.085 --> 00:13:10.525
inside of the cristae to the intermembrane space.

00:13:10.525 --> 00:13:12.825
So I like to think about this because it makes you realize,

00:13:12.825 --> 00:13:14.825
you know, we look in textbooks and we take these things

00:13:14.825 --> 00:13:17.325
like mitochondria for granted, like, "Oh yeah, of course.

00:13:17.325 --> 00:13:18.875
"That's where ATP factories are,"

00:13:18.875 --> 00:13:21.685
but it's still an area for visualization research

00:13:21.685 --> 00:13:24.455
to fully understand exactly how they work

00:13:24.455 --> 00:13:25.855
and even how they are structured

00:13:25.855 --> 00:13:28.655
that this Baffle Model where you see these cristae

00:13:28.655 --> 00:13:31.225
kind of just coming in and out of the different sides.

00:13:31.225 --> 00:13:33.885
This is actually no longer the accepted model

00:13:33.885 --> 00:13:36.745
for the actual visualization, the structure of mitochondria.

00:13:36.745 --> 00:13:39.485
Something more like this, something more where

00:13:39.485 --> 00:13:42.315
you have this cristae junction model

00:13:42.315 --> 00:13:46.615
where you have, if I were to draw a cross section

00:13:46.615 --> 00:13:50.025
where this is the,

00:13:50.025 --> 00:13:52.255
I drew the outer membrane and the inner membrane,

00:13:52.255 --> 00:13:54.655
I'll just draw has these little tunnels

00:13:54.655 --> 00:13:59.535
to the actual space inside of the cristae.

00:13:59.535 --> 00:14:03.455
This is actually now the more accepted visualization,

00:14:03.455 --> 00:14:04.725
so I want you to appreciate

00:14:04.725 --> 00:14:06.885
that when in Biology, you read something in a textbook

00:14:06.885 --> 00:14:08.225
you kind of say, "Oh, people have figured all

00:14:08.225 --> 00:14:10.285
"of this stuff out," but people are still think about,

00:14:10.285 --> 00:14:11.625
"Well, how does this structure work?

00:14:11.625 --> 00:14:12.785
"What is the actual structure?" and then,

00:14:12.785 --> 00:14:14.825
"How does it actually let this organelle,

00:14:14.825 --> 00:14:16.755
"this fascinating organelle do all of the things

00:14:16.755 --> 00:14:18.805
"that it needs to do?"


Endomembrane system

WEBVTT
Kind: captions
Language: en

00:00:00.169 --> 00:00:01.548
- [Voiceover] What I wanna do in this video is give

00:00:01.548 --> 00:00:06.298
an overview of the endomembrane system in eukaryotic cells.

00:00:06.298 --> 00:00:10.688
Endomembrane system.

00:00:10.688 --> 00:00:13.938
And at a very high level, the endomembrane system is all

00:00:13.938 --> 00:00:17.770
of the membranes that interact with each other

00:00:17.770 --> 00:00:18.976
inside of a cell.

00:00:18.976 --> 00:00:20.950
So what membranes are we talking about?

00:00:20.950 --> 00:00:22.505
Well, you can start off by talking

00:00:22.505 --> 00:00:25.223
about the cell membrane itself.

00:00:25.223 --> 00:00:26.593
And all of these membranes,

00:00:26.593 --> 00:00:29.148
these have bilayers of phospholipids.

00:00:29.148 --> 00:00:30.494
Sometimes my brain malfunctions

00:00:30.494 --> 00:00:32.073
and I call them bilipid layers,

00:00:32.073 --> 00:00:34.952
but these are bilayers of phospholipids.

00:00:34.952 --> 00:00:37.645
So if I were to zoom in right over here,

00:00:37.645 --> 00:00:40.385
if I were to zoom in right over there, that line,

00:00:40.385 --> 00:00:45.122
it really is a bilayer of phospholipids,

00:00:45.122 --> 00:00:46.980
so it would look like this.

00:00:46.980 --> 00:00:48.849
So you have your...

00:00:50.549 --> 00:00:53.039
hydrophilic heads pointing ouwards,

00:00:53.039 --> 00:00:57.080
and your hydrophobic tails pointing inwards.

00:00:57.080 --> 00:00:59.030
So hydrophilic heads pointing outwards,

00:00:59.030 --> 00:01:01.282
hydrophobic tails pointing inwards,

00:01:01.282 --> 00:01:02.351
and it keeps going.

00:01:03.401 --> 00:01:05.600
If we think of it from left to right,

00:01:05.600 --> 00:01:07.595
you have a layer of two,

00:01:07.595 --> 00:01:10.775
or you have a bilayer, I should say, of phospholipids.

00:01:10.775 --> 00:01:12.706
That's going to be true of the cellular membrane,

00:01:12.706 --> 00:01:13.857
that's going to be true

00:01:13.857 --> 00:01:16.947
of the outer nuclear membrane right over here.

00:01:16.947 --> 00:01:20.972
We drew this one on the video on the endoplasmic reticulum.

00:01:20.972 --> 00:01:23.271
And so over here you see these two membranes.

00:01:23.271 --> 00:01:25.732
You might say, "OK, is this a bilayer?"

00:01:25.732 --> 00:01:27.869
No, this is actually two bilayers.

00:01:27.869 --> 00:01:31.398
So this membrane right over here has a phospholipid bilayer,

00:01:31.398 --> 00:01:35.792
and this membrane over here also has a phospholipid...

00:01:36.862 --> 00:01:38.732
a phosopholipid bilayer.

00:01:40.112 --> 00:01:41.260
Let me do this in another color.

00:01:41.260 --> 00:01:45.375
This one that I'm starting to trace in magenta,

00:01:45.375 --> 00:01:48.835
that's the outer membrane of the nuclear envelope,

00:01:48.835 --> 00:01:52.040
and it's continuous with the membrane

00:01:52.040 --> 00:01:54.733
of the endoplasmic reticulum,

00:01:54.733 --> 00:01:57.241
which I'm starting to highlight right over here.

00:01:57.241 --> 00:01:59.107
And then the one that I'm highlighting

00:01:59.107 --> 00:02:01.487
in this purple color,

00:02:01.487 --> 00:02:05.577
this is the inner membrane of the nuclear envelope,

00:02:05.577 --> 00:02:09.083
and all of this is part of the endomembrane system.

00:02:09.083 --> 00:02:10.638
I've already started talking

00:02:10.638 --> 00:02:12.170
about the endoplasmic reticulum,

00:02:12.170 --> 00:02:14.330
and we go into some depth on that on the video

00:02:14.330 --> 00:02:18.903
on the endoplasmic reticulum and the Golgi apparatus,

00:02:18.903 --> 00:02:21.505
but it's also part of the endomembrane system.

00:02:21.505 --> 00:02:24.965
And the endoplasmic reticulum in particular can represent

00:02:24.965 --> 00:02:27.440
up to, or even more than, 50%...

00:02:29.760 --> 00:02:33.231
of the phospholipid membrane associated with the cell.

00:02:33.231 --> 00:02:35.181
And we've talked about what goes on

00:02:35.181 --> 00:02:37.689
in the lumen of the endoplasmic reticulum.

00:02:37.689 --> 00:02:39.916
So this area right over here...

00:02:42.206 --> 00:02:43.678
we've talked about what happens there.

00:02:43.678 --> 00:02:45.792
Proteins can get synthesized.

00:02:45.792 --> 00:02:48.137
Actually, other molecules, like lipids,

00:02:48.137 --> 00:02:49.732
can get synthesized there.

00:02:51.032 --> 00:02:53.733
And then they can go to the smooth ER,

00:02:53.733 --> 00:02:56.125
and then the place where they exit from the smooth ER,

00:02:56.125 --> 00:02:58.841
and we saw that in the video on the endoplasmic reticulum,

00:02:58.841 --> 00:03:00.466
how they can kind of butt out.

00:03:00.466 --> 00:03:04.065
We call this area, it's often called the transitional ER.

00:03:04.065 --> 00:03:06.689
So this area right over here,

00:03:06.689 --> 00:03:09.985
we would call the transitional endoplasmic reticulum.

00:03:09.985 --> 00:03:11.290
Transitional...

00:03:16.760 --> 00:03:19.088
transitional ER is this place

00:03:19.088 --> 00:03:21.758
where these proteins are being butted off,

00:03:21.758 --> 00:03:23.407
and they're butting off in vesicles.

00:03:23.407 --> 00:03:25.915
So this is the transitional ER.

00:03:25.915 --> 00:03:28.585
And all vesicles are are little small compartments

00:03:28.585 --> 00:03:30.280
that have a membrane around it,

00:03:30.280 --> 00:03:33.623
that things like a protein can be transported in.

00:03:33.623 --> 00:03:35.597
And I don't wanna beat a dead horse here,

00:03:35.597 --> 00:03:37.292
but all of these lines that I'm drawing,

00:03:37.292 --> 00:03:38.917
even though I drew it as a single line,

00:03:38.917 --> 00:03:41.611
these are phospholipid bilayers.

00:03:41.611 --> 00:03:42.981
So the membrane might be different,

00:03:42.981 --> 00:03:45.001
the phospholipid bilayers might be different

00:03:45.001 --> 00:03:47.996
when we go from one piece of the membrane to another,

00:03:47.996 --> 00:03:50.457
but they all have that same general notion

00:03:50.457 --> 00:03:53.661
of having this bilayer of phospholipids.

00:03:53.661 --> 00:03:55.287
But just as a review, these proteins,

00:03:55.287 --> 00:03:58.932
they can emerge from the transitional ER,

00:03:58.932 --> 00:04:01.463
they can make their way to the Golgi apparatus.

00:04:01.463 --> 00:04:02.879
And we've already talked about how

00:04:02.879 --> 00:04:06.896
in the Golgi apparatus these proteins can be matured.

00:04:06.896 --> 00:04:08.173
And when I say being matured,

00:04:08.173 --> 00:04:10.379
there's a bunch of enzymes in here,

00:04:10.379 --> 00:04:12.329
there's a bunch of Golgi enzymes in here,

00:04:12.329 --> 00:04:14.489
they can do all sorts of things to the proteins:

00:04:14.489 --> 00:04:16.727
tag them, they can actually add...

00:04:18.167 --> 00:04:19.747
add saccharides to them,

00:04:19.747 --> 00:04:21.849
so that they become glycoproteins.

00:04:21.849 --> 00:04:23.683
They can tag them so they can be used

00:04:23.683 --> 00:04:25.169
in the cellular membrane,

00:04:25.169 --> 00:04:27.027
or be used outside of the cellular membrane,

00:04:27.027 --> 00:04:29.233
or to be used other places in the cell.

00:04:29.233 --> 00:04:32.483
So for example, this protein right over here butted off

00:04:32.483 --> 00:04:37.150
as a vesicle, it makes its way to the Golgi apparatus,

00:04:37.150 --> 00:04:38.660
the membrane can then merge,

00:04:38.660 --> 00:04:42.259
and then dump the protein into the Golgi apparatus.

00:04:42.259 --> 00:04:44.232
From there it can be matured.

00:04:44.232 --> 00:04:46.252
It might turn into a glycoprotein,

00:04:46.252 --> 00:04:47.669
who knows what happens to it?

00:04:47.669 --> 00:04:49.364
And then it could butt off again,

00:04:49.364 --> 00:04:51.523
and then this protein that's now butted off,

00:04:51.523 --> 00:04:56.028
it could go to be embedded into the cellular membrane.

00:04:56.028 --> 00:04:59.000
The protein could be excreted from the cell,

00:04:59.000 --> 00:05:01.600
or it could go to other parts of the cell.

00:05:01.600 --> 00:05:03.273
Everything I've just talked about,

00:05:03.273 --> 00:05:05.640
those aren't the only parts of the endomembrane system.

00:05:05.640 --> 00:05:07.869
You have things like vacuoles,

00:05:07.869 --> 00:05:11.445
which are membrane-bound organelles in a cell.

00:05:11.445 --> 00:05:15.671
In plant cells, a vacuole can be used for storage,

00:05:15.671 --> 00:05:17.807
it could be used for structure.

00:05:17.807 --> 00:05:19.293
Vacuoles can get quite large,

00:05:19.293 --> 00:05:20.454
and they can actually give, kind of,

00:05:20.454 --> 00:05:22.962
the structure of the actual plant.

00:05:22.962 --> 00:05:27.304
In animal cells, you might have something called a lysosome.

00:05:27.304 --> 00:05:29.370
And a lysosome is a membrane-bound structure

00:05:29.370 --> 00:05:32.110
where, essentially, things go to, for the most part,

00:05:32.110 --> 00:05:35.639
be recycled, or to be torn apart.

00:05:35.639 --> 00:05:38.943
So maybe something got packaged from someplace.

00:05:40.903 --> 00:05:42.272
Let me do this in another color.

00:05:43.192 --> 00:05:45.925
And I drew that vesicle a little bit too big.

00:05:45.925 --> 00:05:47.736
But maybe this stuff, it needs to be destroyed,

00:05:47.736 --> 00:05:51.730
so this membrane, it can then merge with that membrane

00:05:51.730 --> 00:05:55.143
and dump its contents in here,

00:05:55.143 --> 00:05:58.649
and this has a low pH, and it can actually, kind of,

00:05:58.649 --> 00:06:01.272
break apart this stuff, and it can digest this stuff,

00:06:01.272 --> 00:06:04.755
and recycle it into its, I guess you could say,

00:06:04.755 --> 00:06:06.451
more constituent material.

00:06:06.451 --> 00:06:11.187
So all of this is part of the endomembrane system.

00:06:11.187 --> 00:06:12.790
So once again, I don't think there's an appreciation

00:06:12.790 --> 00:06:13.997
for how complex

00:06:13.997 --> 00:06:17.433
and, on a lot of levels, beautiful cells can be.


Intuition behind formula for thermal conductivity

WEBVTT
Kind: captions
Language: en

00:00:00.390 --> 00:00:02.650
- So I have an interesting system over here.

00:00:02.650 --> 00:00:05.520
I have two compartments, on the left compartment

00:00:05.520 --> 00:00:09.750
I have a gas that is at a temperature of T sub a

00:00:09.750 --> 00:00:12.550
and on the right side of this I have gas

00:00:12.550 --> 00:00:15.050
that is a temperature of T sub b

00:00:15.050 --> 00:00:19.850
and they are separated by a wall of depth, d,

00:00:19.850 --> 00:00:22.020
or I guess you say of thickness, d,

00:00:22.020 --> 00:00:25.420
and the contact area of the wall,

00:00:25.420 --> 00:00:27.820
or the contact area of the gas onto the wall

00:00:27.820 --> 00:00:29.890
that area is A, and I'm just drawing

00:00:29.890 --> 00:00:31.520
a section of it, we're assuming that

00:00:31.520 --> 00:00:34.750
these two compartments are completely separated.

00:00:34.750 --> 00:00:36.390
Now what I am curious about, and we're

00:00:36.390 --> 00:00:38.580
going to assume that the temperature on the left

00:00:38.580 --> 00:00:40.950
is higher than the temperature on the right,

00:00:40.950 --> 00:00:42.290
and so because of that you're going to have

00:00:42.290 --> 00:00:45.850
a transfer of thermal energy from the left to the right,

00:00:45.850 --> 00:00:47.890
and that thermal energy that gets transferred

00:00:47.890 --> 00:00:51.320
we call that heat, and we'll denote that with the letter Q,

00:00:51.320 --> 00:00:53.420
I'm curious about how does the rate

00:00:53.420 --> 00:00:55.020
at which heat is transferred, or so

00:00:55.020 --> 00:00:57.550
how much heat is transferred per unit time,

00:00:57.550 --> 00:00:59.090
that's the rate at which heat is transferred,

00:00:59.090 --> 00:01:01.150
how would that change depending on

00:01:01.150 --> 00:01:03.680
how we change these different variables.

00:01:03.680 --> 00:01:07.560
So for example, if our, if our area,

00:01:07.560 --> 00:01:10.460
if our contact area were to go up

00:01:10.460 --> 00:01:13.150
what would that do for Q over t?

00:01:13.150 --> 00:01:16.490
Well then Q over t would also increase per unit time

00:01:16.490 --> 00:01:19.520
'cause I have, I have more area for these

00:01:19.520 --> 00:01:23.290
hot molec--these hot air particles or hot air molecules

00:01:23.290 --> 00:01:25.080
to bump into and they'll heat that wall

00:01:25.080 --> 00:01:26.820
and then there will be more heated wall

00:01:26.820 --> 00:01:29.890
to heat up the colder air particles.

00:01:29.890 --> 00:01:34.120
So in that case our rate of heat transfer would also go up.

00:01:34.120 --> 00:01:37.420
Well what if we, what if we, and obviously if I made

00:01:37.420 --> 00:01:40.520
my area smaller, maybe I should just write that explicitly,

00:01:40.520 --> 00:01:43.820
if I made my contact area smaller then my rate

00:01:43.820 --> 00:01:46.350
of heat transfer, my rate of heat transfer

00:01:46.350 --> 00:01:49.520
would go down, and that feels like common sense.

00:01:49.520 --> 00:01:52.320
Now what about, what about the thickness?

00:01:52.320 --> 00:01:54.850
If I were to make it, if I were to make

00:01:54.850 --> 00:01:57.150
the thickness larger, if I were to make this a thicker wall,

00:01:57.150 --> 00:01:59.490
what would that do to my rate of heat transfer?

00:01:59.490 --> 00:02:01.250
Well then I would have, I would have more

00:02:01.250 --> 00:02:02.950
things that I would have to heat up to get it

00:02:02.950 --> 00:02:06.530
to a certain temperature before I can,

00:02:06.530 --> 00:02:09.720
which then can heat up the particles on the right,

00:02:09.720 --> 00:02:11.250
and obviously this is a continuous process,

00:02:11.250 --> 00:02:13.390
it'll always be happening, but there will just be more

00:02:13.390 --> 00:02:15.720
stuff to heat up and it's going to take longer

00:02:15.720 --> 00:02:17.690
and more of that, and more of that

00:02:17.690 --> 00:02:19.520
more of that kinetic energy, that average

00:02:19.520 --> 00:02:21.550
kinetic energy is going to get dissipated

00:02:21.550 --> 00:02:25.210
in this wall so if this wall becomes thicker,

00:02:25.210 --> 00:02:27.200
if the wall becomes thicker then the

00:02:27.200 --> 00:02:30.150
rate of heat transfer is going to go down,

00:02:30.150 --> 00:02:32.920
or if you, if the wall became thinner,

00:02:32.920 --> 00:02:36.890
if this depth decreased then the rate of heat transfer,

00:02:36.890 --> 00:02:39.550
then the rate of heat transfer would go up.

00:02:39.550 --> 00:02:40.780
So you could say the rate of heat transfer

00:02:40.780 --> 00:02:43.240
is going to be inversely proportional

00:02:43.240 --> 00:02:46.120
to the thickness of this wall.

00:02:46.120 --> 00:02:47.850
Now what else could we think about?

00:02:47.850 --> 00:02:51.450
Well we could think about the temperature differential,

00:02:51.450 --> 00:02:55.880
the temperature differential, that's T sub a minus,

00:02:55.880 --> 00:03:00.400
minus T sub b, minus T sub b.

00:03:00.400 --> 00:03:02.890
Well if this temperature differential, if this

00:03:02.890 --> 00:03:05.090
temperature differential were to go up,

00:03:05.090 --> 00:03:06.720
well what's going to happen?

00:03:06.720 --> 00:03:09.320
Well it's common sense that well if this is super hot,

00:03:09.320 --> 00:03:11.890
if this is super hot over here, this is way hotter

00:03:11.890 --> 00:03:13.080
than what we have on the right,

00:03:13.080 --> 00:03:15.320
well we're going to have more heat transferred

00:03:15.320 --> 00:03:17.650
so the rate of heat transfer, you're going to have

00:03:17.650 --> 00:03:19.050
more heat transferred per unit time,

00:03:19.050 --> 00:03:22.890
your rate of heat transfer is going to go up.

00:03:22.890 --> 00:03:25.810
And likewise, if this differential were to go down

00:03:25.810 --> 00:03:26.920
and you could take the extreme case

00:03:26.920 --> 00:03:28.620
if there was no differential,

00:03:28.620 --> 00:03:31.550
if T sub a was the same as T sub b

00:03:31.550 --> 00:03:33.920
then you would have no heat transfer

00:03:33.920 --> 00:03:36.050
frankly in any unit of time.

00:03:36.050 --> 00:03:37.920
So it makes sense that the rate of heat transfer

00:03:37.920 --> 00:03:42.050
is going to be proportional to the temperature differential.

00:03:42.050 --> 00:03:44.680
So how can we encapsulate all of this intuition

00:03:44.680 --> 00:03:47.770
into maybe a formula for describing

00:03:47.770 --> 00:03:51.350
thermal conductivity, for thinking about

00:03:51.350 --> 00:03:53.720
how quickly some, how quickly this heat

00:03:53.720 --> 00:03:56.350
will be transferred, the rate of heat transfer?

00:03:56.350 --> 00:03:59.650
Well we could say the rate of heat transfer,

00:03:59.650 --> 00:04:02.050
and this is really, hopefully you know comes out of

00:04:02.050 --> 00:04:04.250
a little bit of common sense or intuition

00:04:04.250 --> 00:04:05.970
of what would happen here, the rate of

00:04:05.970 --> 00:04:09.190
heat transfer, I could say it's going to be proportional to

00:04:09.190 --> 00:04:11.150
well, what are the things it's going to be proportional to?

00:04:11.150 --> 00:04:13.090
It's going to be proportional to the area,

00:04:13.090 --> 00:04:14.990
the more surface area we have on this wall,

00:04:14.990 --> 00:04:17.820
more contact area, the more heat we're going

00:04:17.820 --> 00:04:19.650
to have transferred per unit time,

00:04:19.650 --> 00:04:23.420
so it's going to be proportional to that contact area.

00:04:23.420 --> 00:04:24.680
It's also going to be proportional to

00:04:24.680 --> 00:04:26.990
the temperature differential so let's multiply

00:04:26.990 --> 00:04:30.190
this times the temperature differential,

00:04:30.190 --> 00:04:34.690
so T sub a minus T sub b,

00:04:34.690 --> 00:04:36.370
minus T sub b,

00:04:36.370 --> 00:04:38.050
and it's inversely proportional to

00:04:38.050 --> 00:04:41.150
the thickness of the wall so all of that

00:04:41.150 --> 00:04:43.450
over the thickness of the wall.

00:04:43.450 --> 00:04:44.820
And now another thing that you might be saying,

00:04:44.820 --> 00:04:46.780
okay I have this proportionality constant

00:04:46.780 --> 00:04:48.920
but wouldn't this be different for different materials?

00:04:48.920 --> 00:04:50.920
For example, if this was a metal wall

00:04:50.920 --> 00:04:52.990
wouldn't this conduct the heat quicker

00:04:52.990 --> 00:04:54.750
than if this was a wood wall?

00:04:54.750 --> 00:04:56.960
And you would be correct, a metal wall would

00:04:56.960 --> 00:04:59.790
and so this K, this K right over here,

00:04:59.790 --> 00:05:02.650
this is dependent, this is dependent on

00:05:02.650 --> 00:05:05.150
the material, so what is the wall made of.

00:05:05.150 --> 00:05:06.740
So material...

00:05:06.740 --> 00:05:10.580
material of the wall,

00:05:10.580 --> 00:05:12.250
and you can actually, you can actually

00:05:12.250 --> 00:05:14.560
measure this thing and different materials

00:05:14.560 --> 00:05:16.850
will have different thermal conductivities,

00:05:16.850 --> 00:05:18.610
which this, which this variable

00:05:18.610 --> 00:05:21.120
right over here would actually represent.

00:05:21.120 --> 00:05:22.720
So going through a little bit of intuition

00:05:22.720 --> 00:05:24.350
we were able to come up with what looks like

00:05:24.350 --> 00:05:27.150
a fancy formula, and you will sometimes see

00:05:27.150 --> 00:05:29.920
this formula, formula for thermal conductivity

00:05:29.920 --> 00:05:33.320
through a solid barrier but it really comes out of

00:05:33.320 --> 00:05:35.120
hopefully common sense, the rate of,

00:05:35.120 --> 00:05:37.420
the amount of heat transferred per time

00:05:37.420 --> 00:05:39.020
is going to be proportional to,

00:05:39.020 --> 00:05:40.620
and the proportionality constant is going

00:05:40.620 --> 00:05:41.450
to be dependent on the material.

00:05:41.450 --> 00:05:43.550
Styrofoam for example would be very low here,

00:05:43.550 --> 00:05:45.830
that's why coolers are made out of Styrofoam,

00:05:45.830 --> 00:05:47.890
and it's going to be dependent on the area,

00:05:47.890 --> 00:05:49.420
it's going to be proportional to the area,

00:05:49.420 --> 00:05:50.920
the temperature differential, and then

00:05:50.920 --> 00:05:53.320
inversely proportional to the thickness.

00:05:53.320 --> 00:05:56.010
So if you wanted to really insulate something

00:05:56.010 --> 00:05:58.520
you would want to minimize the surface area

00:05:58.520 --> 00:06:00.750
and you would want to, and you would want to

00:06:00.750 --> 00:06:03.010
maximize the thickness and you would want to

00:06:03.010 --> 00:06:06.290
have something with a very low thermal conductivity,

00:06:06.290 --> 00:06:10.860
so a thick Styrofoam wall that's maybe shaped in a sphere

00:06:10.860 --> 00:06:13.740
might be a pretty good container for keeping

00:06:13.740 --> 00:06:16.401
something hot or for keeping something cool.


Thermal conductivity of metal and wood

WEBVTT
Kind: captions
Language: en

00:00:00.121 --> 00:00:01.514
- [Voiceover] So if you're in a room of some kind

00:00:01.514 --> 00:00:04.068
I encourage you to try a little experiment right now.

00:00:04.068 --> 00:00:05.415
So look around the room

00:00:05.415 --> 00:00:06.854
and see if there's something in the room

00:00:06.854 --> 00:00:11.127
that's made out of wood, or maybe paper, or cloth,

00:00:11.127 --> 00:00:13.843
and it's been in the room for some time,

00:00:13.843 --> 00:00:15.933
so hopefully it has the temperature of the room.

00:00:15.933 --> 00:00:18.139
And then find something else that's made out of metal

00:00:18.139 --> 00:00:20.368
that's also been sitting in the room for awhile

00:00:20.368 --> 00:00:22.179
and it doesn't have its own source of energy,

00:00:22.179 --> 00:00:23.108
so don't use your computer.

00:00:23.108 --> 00:00:24.219
It should just be something that's been

00:00:24.219 --> 00:00:25.724
passively sitting in that room for awhile,

00:00:25.724 --> 00:00:27.164
it's not too hard to find,

00:00:27.164 --> 00:00:29.068
and touch them both.

00:00:29.068 --> 00:00:30.543
And what you will see, is that even though

00:00:30.543 --> 00:00:32.656
they've both been sitting in that room for awhile,

00:00:32.656 --> 00:00:36.208
the metal is going to feel a lot colder.

00:00:36.208 --> 00:00:38.530
The metal is going to feel colder.

00:00:38.530 --> 00:00:40.109
And this is a bit of a conundrum

00:00:40.109 --> 00:00:42.710
because they've both been sitting in this room

00:00:42.710 --> 00:00:44.985
for a while, so they both should take on

00:00:44.985 --> 00:00:46.634
the ambient temperature.

00:00:46.634 --> 00:00:48.120
So let's make this a little bit more concrete.

00:00:48.120 --> 00:00:50.117
Let's say that the temperature of the room

00:00:50.117 --> 00:00:52.671
is 70 degrees fahrenheit.

00:00:52.671 --> 00:00:54.528
And the key for this feeling colder,

00:00:54.528 --> 00:00:56.432
is that the ambient temperature of the room

00:00:56.432 --> 00:00:59.729
is less than your body temperature.

00:00:59.729 --> 00:01:01.169
Your body temperature is going to be

00:01:01.169 --> 00:01:07.031
roughly 98.6 degrees fahrenheit.

00:01:07.031 --> 00:01:10.427
So let me write this, this is body temperature.

00:01:10.427 --> 00:01:11.750
And the temperature at the surface

00:01:11.750 --> 00:01:13.538
of your skin might be a little bit different than this,

00:01:13.538 --> 00:01:14.931
but let's just assume that it's

00:01:14.931 --> 00:01:19.064
roughly 98.6 degrees fahrenheit.

00:01:19.064 --> 00:01:21.293
And so, what's happening is, this metal one,

00:01:21.293 --> 00:01:24.683
this metal surface, isn't actually colder.

00:01:24.683 --> 00:01:26.076
It doesn't actually have a lower average

00:01:26.076 --> 00:01:29.466
kinetic energy than the wood surface.

00:01:29.466 --> 00:01:31.951
They've both been sitting in this room for a while,

00:01:31.951 --> 00:01:33.762
they're both going to have the ambient temperature

00:01:33.762 --> 00:01:38.336
of 70 degrees fahrenheit.

00:01:38.336 --> 00:01:39.218
So what just happened?

00:01:39.218 --> 00:01:42.515
Why, to your skin, and to your brain,

00:01:42.515 --> 00:01:45.743
does the metal actually feel colder?

00:01:45.743 --> 00:01:47.693
And the simple answer is, it's better

00:01:47.693 --> 00:01:50.383
at taking the heat away from you.

00:01:50.383 --> 00:01:53.610
So why is it better at taking the heat away from me?

00:01:53.610 --> 00:01:57.093
Well, let's just imagine, let's say that these

00:01:57.093 --> 00:02:05.475
here are the atoms on the surface of my skin.

00:02:05.475 --> 00:02:07.542
So these are the atoms on the surface of my skin,

00:02:07.542 --> 00:02:09.237
the bottom of my skin, let's just say my hand

00:02:09.237 --> 00:02:11.024
is touching a surface like this.

00:02:11.024 --> 00:02:12.255
That's my thumb right over there,

00:02:12.255 --> 00:02:13.578
and I'm touching the surface.

00:02:13.578 --> 00:02:16.342
And it's going to have an average kinetic energy

00:02:16.342 --> 00:02:19.012
that would be in relation to a body temperature

00:02:19.012 --> 00:02:21.821
of 98.6 degrees fahrenheit.

00:02:21.821 --> 00:02:23.377
So these things are going to bounce around,

00:02:23.377 --> 00:02:26.264
or vibrate around.

00:02:28.134 --> 00:02:30.215
And maybe the covalent bonds between

00:02:30.215 --> 00:02:34.394
the carbon atoms and the other atoms

00:02:34.394 --> 00:02:37.784
on my skin that keeps them from breaking free fully,

00:02:37.784 --> 00:02:40.106
but they're going to be kind of oscillating around,

00:02:40.106 --> 00:02:41.870
bouncing around a little bit.

00:02:41.870 --> 00:02:44.680
And they'll even kind of push on each other,

00:02:44.680 --> 00:02:47.662
and this could be kind of the electrostatic forces doing it.

00:02:47.662 --> 00:02:50.401
But they're going to have some average kinetic energy.

00:02:50.401 --> 00:02:52.468
And let's say my hand is touching both of these

00:02:52.468 --> 00:02:54.186
surfaces at the same time.

00:02:54.186 --> 00:03:03.009
So I have the wood surface, I'll do that in yellow.

00:03:03.009 --> 00:03:05.656
So I have the wood surface, right over there.

00:03:05.656 --> 00:03:07.235
That is wood.

00:03:07.235 --> 00:03:10.509
And I have the metal surface, I'll do that in white.

00:03:10.509 --> 00:03:13.667
So I have the metal surface, right over here.

00:03:13.667 --> 00:03:15.176
And this metal surface, we already talked about,

00:03:15.176 --> 00:03:17.939
is going to feel colder.

00:03:17.939 --> 00:03:19.727
Let me draw the rest of my hand, actually.

00:03:19.727 --> 00:03:27.389
So the rest of my arm, you get the idea.

00:03:27.389 --> 00:03:29.154
So what's going on here.

00:03:29.154 --> 00:03:32.265
So let's just think about it at a microscopic level.

00:03:32.265 --> 00:03:33.658
So the wood, first of all, its surface

00:03:33.658 --> 00:03:34.982
is going to be uneven.

00:03:34.982 --> 00:03:37.133
So you're going to have atoms up here,

00:03:37.133 --> 00:03:39.084
but then you're going to have gaps,

00:03:39.084 --> 00:03:40.709
there's going to be air here.

00:03:40.709 --> 00:03:42.613
Let me actually scroll down a little bit.

00:03:42.613 --> 00:03:45.004
So it's going to be like this,

00:03:45.004 --> 00:03:49.718
so you're going to have gaps like that.

00:03:49.718 --> 00:03:57.450
And it also has internal gaps, like that.

00:03:57.450 --> 00:03:59.029
So this would be the wood,

00:03:59.029 --> 00:04:02.024
while the metal is much denser.

00:04:02.024 --> 00:04:05.019
And the surface is actually much smoother.

00:04:05.019 --> 00:04:08.711
So the metal, let me do the metal in that white color,

00:04:08.711 --> 00:04:14.841
the metal atoms are much more closely packed.

00:04:14.841 --> 00:04:19.183
It is much denser, the surface is smoother,

00:04:19.183 --> 00:04:22.642
it won't have any internal air pockets,

00:04:22.642 --> 00:04:25.940
it's not going to have any internal air pockets in it.

00:04:25.940 --> 00:04:27.542
And so what's going to happen?

00:04:27.542 --> 00:04:29.515
Well, we've always said, you're going to have

00:04:29.515 --> 00:04:34.763
a transfer of heat from the higher temperature system,

00:04:34.763 --> 00:04:36.295
or the higher temperature thing,

00:04:36.295 --> 00:04:37.526
to the lower temperature thing.

00:04:37.526 --> 00:04:40.057
And so, they're already going to have some kinetic energy,

00:04:40.057 --> 00:04:42.448
these things are going to have an average kinetic energy

00:04:42.448 --> 00:04:47.882
that's consistent with 70 degrees fahrenheit.

00:04:47.882 --> 00:04:50.459
So, let me just draw a couple of these arrows.

00:04:50.459 --> 00:04:51.689
Same thing over here, they're going to have

00:04:51.689 --> 00:04:54.963
the same average kinetic energy.

00:04:54.963 --> 00:04:57.308
So these things are all jostling around,

00:04:57.308 --> 00:04:59.073
bouncing around and pushing on each other

00:04:59.073 --> 00:05:02.092
with the electrostatic forces.

00:05:02.092 --> 00:05:06.155
So, hopefully this gives you an idea of things.

00:05:06.155 --> 00:05:08.059
But, my hand is warmer,

00:05:08.059 --> 00:05:10.288
my hand has a higher average kinetic energy.

00:05:10.288 --> 00:05:13.631
And so the atoms and molecules of my hand

00:05:13.631 --> 00:05:14.607
are going to bounce into

00:05:14.607 --> 00:05:17.788
the atoms and molecules of the wood,

00:05:17.788 --> 00:05:20.806
and they're going to transfer the kinetic energy.

00:05:20.806 --> 00:05:22.617
But we realize in the wood is,

00:05:22.617 --> 00:05:24.150
I'm making less contact.

00:05:24.150 --> 00:05:27.029
Because, first of all, the surface of the wood isn't smooth,

00:05:27.029 --> 00:05:28.608
so I'm making less contact.

00:05:28.608 --> 00:05:30.442
So this one over here might just bump into

00:05:30.442 --> 00:05:31.835
another air particle, it actually won't

00:05:31.835 --> 00:05:33.344
bump into a wood particle.

00:05:33.344 --> 00:05:35.063
But some of the wood particles will start to

00:05:35.063 --> 00:05:39.219
take some of the kinetic energy away from me.

00:05:39.219 --> 00:05:41.308
And I will sense that as being a little bit cool,

00:05:41.308 --> 00:05:42.841
so maybe that takes a little kinetic energy,

00:05:42.841 --> 00:05:44.095
that bumps into this guy.

00:05:44.095 --> 00:05:47.717
So the kinetic energy does get transferred down.

00:05:47.717 --> 00:05:50.108
But it's going to be transferred down a lot slower

00:05:50.108 --> 00:05:51.803
than what would happen in the metal.

00:05:51.803 --> 00:05:54.683
Because, one, I don't have as much surface contact

00:05:54.683 --> 00:05:56.006
between my hand and the wood,

00:05:56.006 --> 00:05:57.097
because of these gaps.

00:05:57.097 --> 00:06:02.020
I also have air pockets in the wood, like this.

00:06:02.020 --> 00:06:03.831
And in general, the wood is less dense.

00:06:03.831 --> 00:06:06.246
So, there's going to be less collisions

00:06:06.246 --> 00:06:07.407
and it's going to take more time

00:06:07.407 --> 00:06:09.520
for that kinetic energy to be transferred

00:06:09.520 --> 00:06:11.377
away from my hand.

00:06:11.377 --> 00:06:12.724
And the metal, on the other hand,

00:06:12.724 --> 00:06:16.787
as soon as this atom bumps into this one,

00:06:16.787 --> 00:06:18.134
that's going to bump into that one,

00:06:18.134 --> 00:06:19.063
that's going to bump into that one,

00:06:19.063 --> 00:06:20.409
that's going to bump into that one.

00:06:20.409 --> 00:06:21.640
And that kinetic energy is going to be

00:06:21.640 --> 00:06:27.375
very quickly transferred down the metal.

00:06:27.375 --> 00:06:30.092
So it's going to be able to take more heat away from me.

00:06:30.092 --> 00:06:33.482
So this molecule over here is going to get

00:06:33.482 --> 00:06:36.941
some kinetic energy from a molecule in my hand.

00:06:36.941 --> 00:06:39.747
But then, it's going to bump into it's neighbor

00:06:39.747 --> 00:06:41.210
and transfer that kinetic energy.

00:06:41.210 --> 00:06:43.741
So it's going to lose it's kinetic energy quite quickly,

00:06:43.741 --> 00:06:45.993
and so it's ready to be bumped into again

00:06:45.993 --> 00:06:48.199
by another molecule from my hand,

00:06:48.199 --> 00:06:49.708
and take on more kinetic energy.

00:06:49.708 --> 00:06:52.889
So it's going to sap the heat away from me faster.

00:06:52.889 --> 00:06:56.186
So you have faster heat transfer,

00:06:56.186 --> 00:07:00.226
than you have with the wood.

00:07:00.226 --> 00:07:02.966
And, from your body's point of view,

00:07:02.966 --> 00:07:06.658
this heat being sapped away from you faster,

00:07:06.658 --> 00:07:08.051
even though the two surfaces are actually

00:07:08.051 --> 00:07:09.119
the same temperature,

00:07:09.119 --> 00:07:13.043
you perceive this, your body perceives this

00:07:13.043 --> 00:07:20.305
right over here as being colder.


Thermal conduction

WEBVTT
Kind: captions
Language: en

00:00:00.226 --> 00:00:02.420
- Let say that I have two different gases

00:00:02.420 --> 00:00:03.593
at two different temperatures

00:00:03.593 --> 00:00:06.252
that just got in contact with each other.

00:00:06.252 --> 00:00:08.922
So, this is my magenta gas.

00:00:08.922 --> 00:00:11.290
Right over here, let me draw a bunch of

00:00:11.290 --> 00:00:14.390
the molecules of my

00:00:14.390 --> 00:00:17.757
magenta gas right over here.

00:00:17.757 --> 00:00:19.754
And it's just, this system over here,

00:00:19.754 --> 00:00:21.217
I guess, whatever you want to call it,

00:00:21.217 --> 00:00:24.474
has just come in contact with this blue gas.

00:00:24.851 --> 00:00:28.874
This blue gas, right over here.

00:00:30.017 --> 00:00:31.921
And lets say that right where when we're starting

00:00:31.921 --> 00:00:33.953
our simulation, our experiment,

00:00:33.953 --> 00:00:37.837
that this magenta gas has a higher temperature.

00:00:38.376 --> 00:00:41.134
Higher temperature.

00:00:41.546 --> 00:00:43.770
And our blue gas has a lower temperature.

00:00:44.286 --> 00:00:46.939
Lower temperature.

00:00:47.154 --> 00:00:50.114
So lets just remind ourselves what temperature is.

00:00:50.114 --> 00:00:52.517
Specially if we think about it on a molecular scale.

00:00:52.517 --> 00:00:54.990
So higher temperature, lower temperature.

00:00:54.990 --> 00:00:59.193
Temperature is proportional to average kinetic energy.

00:00:59.193 --> 00:01:02.316
So these molecules, they're gonna be vibrating around,

00:01:02.316 --> 00:01:03.849
they're gonna be bumping around.

00:01:03.849 --> 00:01:04.661
They're gonna have,

00:01:04.661 --> 00:01:06.356
each of them are gonna have kinetic energy

00:01:06.356 --> 00:01:07.320
and if you average them,

00:01:07.320 --> 00:01:09.549
that's gonna be proportional to temperature.

00:01:09.549 --> 00:01:12.219
So let me depict each of this individual

00:01:12.219 --> 00:01:13.659
molecule's kinetic energy.

00:01:13.659 --> 00:01:15.087
Maybe this one is doing that.

00:01:15.087 --> 00:01:16.922
Maybe this one is doing that.

00:01:16.922 --> 00:01:18.617
Maybe this one is going in this direction.

00:01:18.617 --> 00:01:20.288
Maybe that one is going that direction.

00:01:20.288 --> 00:01:22.617
That one is going in that direction.

00:01:22.617 --> 00:01:24.570
This is going in that direction.

00:01:24.570 --> 00:01:26.221
That is going in that direction.

00:01:26.221 --> 00:01:27.203
So,

00:01:27.626 --> 00:01:29.623
notice, they all have different directions.

00:01:29.623 --> 00:01:32.421
And the magnitude of their velocity can be different.

00:01:32.421 --> 00:01:34.273
They all have different speeds.

00:01:34.627 --> 00:01:37.501
They all might have different speeds.

00:01:38.226 --> 00:01:39.886
So they have different speeds right over here.

00:01:39.886 --> 00:01:42.359
And they're all bumping into each other.

00:01:42.359 --> 00:01:43.857
Transferring their kinetic energy,

00:01:43.857 --> 00:01:45.157
transferring their momentum

00:01:45.157 --> 00:01:47.328
to from one particle to another.

00:01:47.328 --> 00:01:48.408
But when we talk about temperature

00:01:48.408 --> 00:01:49.987
we talk about the average kinetic energy

00:01:49.987 --> 00:01:51.055
or what's proportional to the

00:01:51.055 --> 00:01:52.837
average kinetic energy of the system.

00:01:53.121 --> 00:01:54.654
Well this one, each of these molecules

00:01:54.654 --> 00:01:57.025
are also gonna have some kinetic energy.

00:01:57.405 --> 00:01:59.193
But on average it's gonna be lower.

00:01:59.193 --> 00:02:01.156
Maybe this one is doing something like this.

00:02:01.156 --> 00:02:03.222
This one is doing something like this.

00:02:03.222 --> 00:02:05.161
This is doing something like this.

00:02:05.161 --> 00:02:07.431
This is doing something like this.

00:02:07.646 --> 00:02:08.957
So they're different,

00:02:08.957 --> 00:02:11.111
but on average they're gonna be lower.

00:02:11.152 --> 00:02:12.046
So,

00:02:12.046 --> 00:02:14.019
hopefully you see that this magenta arrows

00:02:14.019 --> 00:02:17.491
are bigger than these blue arrows

00:02:17.491 --> 00:02:18.739
that I'm doing.

00:02:19.047 --> 00:02:20.080
And they don't all have to be,

00:02:20.080 --> 00:02:21.322
for example this one

00:02:21.322 --> 00:02:22.622
might have a lot of kinetic energy.

00:02:22.622 --> 00:02:23.760
But when you average it out,

00:02:23.760 --> 00:02:26.309
the average here is gonna be lower than the average here.

00:02:26.790 --> 00:02:28.863
So, just like that.

00:02:29.112 --> 00:02:30.761
Now, if this is our initial state,

00:02:30.761 --> 00:02:33.629
what do we think is going to start happening?

00:02:33.629 --> 00:02:36.717
Well, before our different groups of gases

00:02:36.717 --> 00:02:39.724
were colliding with itself

00:02:39.724 --> 00:02:41.454
or the magenta was colliding with the magenta.

00:02:41.454 --> 00:02:42.684
The blue is colliding with the blue.

00:02:42.684 --> 00:02:44.821
But now they're gonna start colliding with each other.

00:02:44.821 --> 00:02:46.423
And so you can imagine when

00:02:46.423 --> 00:02:48.524
this molecule right over here,

00:02:48.524 --> 00:02:50.092
collides with this molecule,

00:02:50.092 --> 00:02:52.390
it's gonna transfer some kinetic energy to it.

00:02:52.390 --> 00:02:56.256
So after the collision, this one might be going.

00:02:56.256 --> 00:02:58.469
After the collision.

00:02:58.555 --> 00:03:00.088
So lets just say they just bounced in to.

00:03:00.088 --> 00:03:01.353
So this is right before,

00:03:01.353 --> 00:03:03.670
and lets say they just finished bouncing into each other.

00:03:03.954 --> 00:03:06.520
So right after they finish bouncing into each other,

00:03:06.520 --> 00:03:08.476
this one might ricochet off.

00:03:08.656 --> 00:03:11.634
So this one is going to go this way.

00:03:11.721 --> 00:03:13.074
Let me do this in a different color.

00:03:13.486 --> 00:03:16.214
So it might hit this one, bounce off,

00:03:16.214 --> 00:03:18.048
and then transfer some of its kinetic energy

00:03:18.048 --> 00:03:20.521
and then it bounces off in this direction.

00:03:20.521 --> 00:03:23.586
While this one, after the collision,

00:03:23.586 --> 00:03:27.099
after the collision is going to

00:03:27.220 --> 00:03:29.357
is maybe going to move

00:03:29.357 --> 00:03:31.853
much faster in this direction.

00:03:31.853 --> 00:03:34.082
And so notice, you have a transfer of energy.

00:03:34.082 --> 00:03:35.823
Just with that one collision you had

00:03:35.823 --> 00:03:37.251
a transfer of kinetic energy

00:03:37.251 --> 00:03:39.457
from this molecule to that molecule.

00:03:39.457 --> 00:03:41.791
And this is going to happen throughout the system.

00:03:41.791 --> 00:03:44.624
That the faster molecules, the ones with more kinetic energy

00:03:44.624 --> 00:03:48.118
as they collide you're gonna have transfer of energy.

00:03:48.118 --> 00:03:49.953
So you're gonna have a

00:03:49.953 --> 00:03:52.217
transfer of energy from the higher temperature

00:03:52.217 --> 00:03:53.639
to the lower temperature.

00:03:53.819 --> 00:03:59.096
Transfer, transfer of energy.

00:03:59.357 --> 00:04:01.121
And this transfer of energy.

00:04:01.121 --> 00:04:03.525
And you can consider this transfer of thermal energy,

00:04:03.525 --> 00:04:04.918
we're talking about temperature here.

00:04:04.918 --> 00:04:07.716
So, the things that are related to temperature,

00:04:07.716 --> 00:04:08.726
we would say thermal.

00:04:08.726 --> 00:04:11.971
So these, this is transfer of thermal energy.

00:04:12.592 --> 00:04:14.426
Transfer of thermal energy.

00:04:14.426 --> 00:04:15.959
The amount, so you're gonna have,

00:04:15.959 --> 00:04:18.954
if you're gonna start with higher energy here.

00:04:18.954 --> 00:04:20.382
You have higher average kinetic energy.

00:04:20.382 --> 00:04:22.356
You have lower average kinetic energy here.

00:04:22.356 --> 00:04:25.421
But this is going to transfer energy

00:04:25.421 --> 00:04:27.790
from the magenta to the blue.

00:04:27.790 --> 00:04:29.183
It's gonna go from higher temperature

00:04:29.183 --> 00:04:30.692
to the lower temperature.

00:04:30.692 --> 00:04:33.153
And that energy that's being transferred,

00:04:33.153 --> 00:04:35.324
that energy that's being transferred,

00:04:35.324 --> 00:04:37.124
we call that, and this is a word that you

00:04:37.124 --> 00:04:39.585
have probably heard many times in your life,

00:04:39.585 --> 00:04:41.861
we call that energy that's being transferred,

00:04:41.861 --> 00:04:43.609
we call that heat.

00:04:43.684 --> 00:04:46.992
That literally this hotter gas over here

00:04:46.992 --> 00:04:48.351
is heating up.

00:04:48.351 --> 00:04:51.358
Is heating up this cooler gas.

00:04:51.358 --> 00:04:53.552
And the way that this transfer of

00:04:53.552 --> 00:04:55.154
thermal energy is happening

00:04:55.154 --> 00:04:57.627
where it's through the collision of the particles,

00:04:57.627 --> 00:05:01.354
the transfer of kinetic energy to the collision of particles

00:05:01.354 --> 00:05:02.724
that's transferred momentum,

00:05:02.724 --> 00:05:04.541
we call this conduction.

00:05:05.220 --> 00:05:07.728
We call this thermal conduction,

00:05:07.728 --> 00:05:09.406
or I'll just call it conduction.

00:05:09.852 --> 00:05:11.972
Let me write thermal conduction.

00:05:12.453 --> 00:05:13.736
I'll do it in a new color.

00:05:14.055 --> 00:05:19.240
So this that is being described is thermal conduction.

00:05:19.489 --> 00:05:21.056
Which is a way that many times

00:05:21.056 --> 00:05:24.121
you have experienced heat being transferred.

00:05:24.121 --> 00:05:26.014
For example, you probably have had

00:05:26.014 --> 00:05:28.057
the experience of,

00:05:28.057 --> 00:05:30.483
if you take a, I don't know,

00:05:30.483 --> 00:05:34.205
you take a pot.

00:05:35.023 --> 00:05:36.933
Lets say you take a pot like this.

00:05:37.217 --> 00:05:39.179
Lets say it's a cold pot at first.

00:05:39.179 --> 00:05:41.687
So its particles, the particles in the pot

00:05:41.687 --> 00:05:44.004
have a lower kinetic energy.

00:05:44.055 --> 00:05:45.536
So I'm not gonna be able to do all of them.

00:05:45.751 --> 00:05:48.061
And then you put it over a fire.

00:05:48.061 --> 00:05:49.971
You put it over a fire.

00:05:50.255 --> 00:05:51.573
Let me see if I can draw it.

00:05:52.693 --> 00:05:54.337
You put it over a fire.

00:05:54.992 --> 00:05:58.220
So this is the fire, this is the fire.

00:05:58.220 --> 00:05:58.793
And we're talking about really

00:05:58.793 --> 00:06:00.124
just heating up the metal of the pot,

00:06:00.124 --> 00:06:02.515
I'm not even concerned about what's in the pot right now.

00:06:02.515 --> 00:06:04.791
So this fire is going to heat up,

00:06:04.791 --> 00:06:07.473
it's gonna heat up the bottom of this pot first.

00:06:07.473 --> 00:06:09.818
And it's actually gonna do it primarily

00:06:09.818 --> 00:06:11.258
through thermal conduction,

00:06:11.258 --> 00:06:14.590
because fire is nothing but super hot air particles

00:06:14.590 --> 00:06:15.983
and those super hot air particles

00:06:15.983 --> 00:06:19.083
are gonna bump in to the metal particles of your pot.

00:06:19.083 --> 00:06:21.428
So these metal particles of this pot,

00:06:21.428 --> 00:06:25.085
they're kinetic energy is going to start going up.

00:06:25.085 --> 00:06:27.361
So this part of the pot is going to start heating up.

00:06:27.361 --> 00:06:30.995
And right when you turn your stove on,

00:06:30.995 --> 00:06:33.351
the top of the pot might still be cool,

00:06:33.351 --> 00:06:35.523
but the bottom is going to get hot very fast.

00:06:35.523 --> 00:06:37.183
But if you just wait a few minutes,

00:06:37.183 --> 00:06:40.283
these metal particles are gonna keep bouncing

00:06:40.283 --> 00:06:41.850
and vibrating into each other.

00:06:41.850 --> 00:06:44.323
And so eventually, the top over here

00:06:44.323 --> 00:06:48.259
is going to get quite hot.

00:06:48.259 --> 00:06:52.038
Is going to get quite hot.

00:06:52.287 --> 00:06:54.621
And the way that the top of this metal got hot

00:06:54.621 --> 00:06:56.920
it was through thermal conduction

00:06:56.920 --> 00:06:59.160
that the metal of the bottom got hot first,

00:06:59.160 --> 00:07:00.786
and then they bounced into their neighbors,

00:07:00.786 --> 00:07:02.284
or vibrated into their neighbors

00:07:02.284 --> 00:07:04.060
and transferred some of that kinetic energy.

00:07:04.060 --> 00:07:06.451
And so once again you see this transfer of heat

00:07:06.451 --> 00:07:10.608
from a higher temperature region,

00:07:10.608 --> 00:07:14.074
to a cooler temperature or lower temperature region.