Thermal conduction, convection, and radiation

WEBVTT
Kind: captions
Language: en

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- When we observe what we call fire

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we have this combustion reaction going on

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and then we see these flames

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what we're really observing

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are the three forms of thermal energy transfer.

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We're observing conduction, conduction,

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convection, convection,

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convection,

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and thermal radiation all at the same time.

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So I'll do this, thermal, thermal radiation,

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thermal radiation.

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And I could say thermal conduction,

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thermal convection, and thermal radiation,

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and the word thermal is just relating to things

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dealing with temperature.

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So what is the conduction going on?

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Well what we have going on in the fuel for our fire,

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so down here the fuel for our fire

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we have our classic combustion reaction

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and I encourage you to watch the video on that

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in our chemistry playlist, or chemistry section

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if you're interested in it.

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But you're taking carbon molecules and their bonds

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and then in the presence of oxygen and some heat

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you have a combustion reaction

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producing carbon dioxide and producing water

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and even more energy than you put into it,

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so it's producing a lot of energy.

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And that energy is going to excite

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the molecules that are around it,

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so you have these molecules,

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you have these molecules

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that end up getting a lot of kinetic energy.

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And remember, temperature is proportional

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to average kinetic energy.

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And so the ones that just combusted,

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or the molecules right near the reaction,

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or maybe the ones that were part of the reaction,

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they're gonna have this really high,

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they're gonna have this really high average kinetic energy

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'cause all of this energy was released

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from that combustion reaction.

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And then they're going to bump into other molecules

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that might not have quite as high kinetic energy,

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but then they're going to transfer that kinetic energy

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through these collisions.

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And we have a whole video on thermal conduction,

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but that's what's happening.

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Things with higher kinetic energy

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are bumping into things with lower kinetic energy

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and transferring some of that kinetic energy

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and they're transferring some of that momentum.

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So that is definitely happening

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when we look at a fire like this,

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that neighboring molecules are bumping

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into other molecules and transferring energy.

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Now convection, this is around the idea

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that hot air is less dense.

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So if we have a bunch of air particles here,

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so let's say this is the cool air up here,

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and it makes sense why cool air

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is going to be more dense than hot air.

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'Cause hot air, these particles have a much higher

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kinetic energy and so they're gonna bump

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into each other and they're gonna push each other

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much further away and get more seperation

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from each other because of that high average kinetic energy.

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But because the hot area is less dense,

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this area right over here is less dense, less dense,

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than the white area, these might be all the same molecule,

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I just made them in different colors to show

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the less dense area and the more dense area,

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it is going to rise, it is going to rise.

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Or you can even think of it

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as a more dense area.

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The more dense area is gonna fall around it,

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it's gonna fall around it, or try to go under it,

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because it is more dense,

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and then the less dense area is going to rise.

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And by doing that,

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you have the hotter molecules are moving upwards

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and then the cold molecules can go down

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to maybe the source of heat, the source of heat,

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the source of energy right over here

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to get heated up more.

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So this right over here is, so hot air rises,

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let me write this, the hot, hot air rises.

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And when we think about it

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it makes room for the cool air to come down

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and then get heated up again.

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And that's what's going on in the fire here.

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You see the combustion reaction,

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combustion reaction occurs right over there,

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let me just hit a different color,

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combustion reaction is occurring in the fuel,

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that super hot air, it's going to rise.

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And that's why it looks like these flames

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are kind of, they're moving upwards,

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they're kind of flickering upwards.

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And you'll also see, and actually we're gonna

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talk about this in thermal radiation,

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is that they also change color as they move upwards.

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But this whole idea of fire moving upwards

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and the hot air,

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if you put your hand up here it's gonna be much hotter

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than if you were to put your hand, say, right here,

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even though in theory this is closer to the flame

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than up here and that's because the hot air,

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the hot air is rising and it's making room for cold air,

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or cooler air, I guess I could say,

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to come down here and be part

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and get heated up again,

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and then it would rise up again.

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And so this convection,

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this idea of the hot air rising

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or the cold air falling,

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this is another form of heat transfer.

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Now the last form that we're observing

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when we're looking at fire is thermal radiation.

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And this is all around the idea

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that if you have charged particles being accelerated

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they're going to release electromagnetic radiation.

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And so you might say, Wait, wait, charged particles,

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where are those being accelerated here?

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Well, we have these molecules that are

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constantly being accelerated as they bump

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into each other,

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the one that's gonna transfer kinetic energy

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from, let's say this one bumps into that,

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it's going to accelerate that in different direction

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and even this one might go in another direction

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and acceleration is a change in velocity

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so it could be the magnitudinal velocity

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or your directional velocity.

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So as they're colliding you have all of these

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accelerational charged particles,

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so let me write this down,

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you have acceleration, acceleration

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of charged particles, charged particles,

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particles,

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and then that releases, that releases,

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electromagnetic radiation,

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that releases electromagnetic radiation.

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I know what you're thinking, Wait wait,

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hold on a second, Sal.

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Okay, I can buy that we have molecules

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that are being accelerated,

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but where is this charged,

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where are you getting this charged particles business?

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Well we have to remember these molecules

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are made up of atoms and atoms are made up of

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charged particles, are made up of protons and electrons.

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And so as you accelerate these

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and the more that you accelerate these

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the more radiation you are going to release.

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And you might say, Okay,

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you said I'm observing that in fire,

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where am I observing radiation?

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Well just the very fact that you can see the fire,

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the light emitted from the fire,

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that is electromagnetic radiation,

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that is electromagnetic radiation.

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It's just the electromagnetic radiation

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in the wavelengths that your eye

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considers to be visible light,

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or that your eye considers to be light.

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Even the particles up here,

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so even the particles up here

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that are still quite hot,

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they are also emitting electromagnetic radiation

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because they're all bumping into each other

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and their electrons and their protons

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are all getting accelerated in different ways,

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they're also releasing electromagnetic radiation,

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but it is at a slower wavelength

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than your eye is capable of perceiving as light.

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If you had an infrared camera

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you would see the flames being much larger.

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You would see them go all the way, all the way up here.

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And if you were to look at the flame closely

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you would see down here right where the

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combustion reaction is happening,

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the flame looks blue.

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And that's because the blue light

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is higher energy light,

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and that's because the particles are being accelerated

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more down here,

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and then it goes from blue to kind of a white

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to a yellow, to a red or to an orange, to a red,

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and then it, to your regular eyes, it disappears.

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But everything, everything that has some temperature

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is releasing electromagnetic radiation.

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And you're like, Okay, well that's all fine,

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I can see it but how is that a form of energy transfer?

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Well, if you're ever sat next to a flame

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you will feel the heat.

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In fact, even if the air between you and the flame is cold

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you would still feel like you're getting warm.

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So if this is a flame right over here,

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so that is fire, and let's say you have cold air,

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cold air, let's say you're at a campfire right over here,

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maybe it's 30, this air right over here is 30 degrees,

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if you are standing right over here

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you would still feel heat,

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you would still feel like you're getting warmed up.

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And that's because that electromagnetic radiation

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is being emitted from the air particles

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that we perceive as fire

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and then that can actually excite particles

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on your skin

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and it will transfer energy to your skin

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and so you feel like you are actually getting warmed up.

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I remember once, this is kind of a strange story,

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but I was on the highway

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and there was a car on fire

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and I was literally, we drove to the far lane

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because it was on fire,

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we're three lanes away from it

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and it kind of exploded.

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I don't think anyone was in it,

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hopefully no one was in it,

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but I remember right when it exploded

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it was an intense, immediate heat that we felt

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through the window of the car,

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and that was electromagnetic radiation.

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That was thermal radiation being released

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by these accelerated particles

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in the air around that explosion,

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which we perceived as a an explosion, or fire,

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but then it was warming up particles on my skin.


The Maxwell–Boltzmann distribution

WEBVTT
Kind: captions
Language: en

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- [Voiceover] So let's think a little bit about the

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Maxwell-Boltzmann distribution.

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And this right over here, this is

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a picture of James Clerk Maxwell.

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And I really like this picture, it's with his

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wife Katherine Maxwell and I guess this is their dog.

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And James Maxwell, he is a titan of physics

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famous for Maxwell's equations.

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He also did some of the foundational work

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on color photography and he was involved in

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thinking about, "Well, what's the distribution

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of speeds of air particles

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of idealized gas particles?"

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And this gentleman over here, this is Ludwig Boltzmann.

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And he's considered the father or one

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of the founding fathers of statistical mechanics.

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And together, through the Maxwell-Boltzman distribution

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they didn't collaborate, but they

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independently came to the same distribution.

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They were able to describe, "Well, what's the

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distribution of the speeds of air particles?"

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So let's back up a little bit or let's just

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do a little bit of a thought experiment.

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So let's say that I have a container here.

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Let's say that I have a container here.

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And let's say it has air.

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And air is actually made up mostly of nitrogen.

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Let's just say it just has only nitrogen in it

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just to simplify things.

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So let me just draw some nitrogen molecules in there.

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And let's say that I have a thermometer.

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I put a thermometer in there.

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And the thermometer

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reads a temperature of 300 Kelvin.

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What does this temperature of 300 Kelvin mean?

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Well, in our everyday life, we have

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kind of a visceral sense of temperature.

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Hey, I don't wanna touch something that's hot.

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It's going to burn me.

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Or that cold thing, it's gonna make me shiver.

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And that's how our brain

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processes this thing called temperature.

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But what's actually going on at a molecular scale?

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Well, temperature, one way to think

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about temperature, this would be a very

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accurate way to think about temperature

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is that tempera-

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I'm spelling it wrong.

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Temperature is proportional to average kinetic energy

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of the molecules in that system.

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So let me write it this way.

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Temperature is proportional to average kinetic energy.

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Average

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kinetic

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energy

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in the system.

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I'll just write average kinetic energy.

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So let's make that a little bit more concrete.

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So let's say that I have two containers.

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So it's one container.

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Whoops.

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And two containers right over here.

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And let's say they have the same

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number of molecules of nitrogen gas

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And I'm just gonna draw 10 here.

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This obviously is not realistic

00:02:38.830 --> 00:02:40.350
you'd have many, many more molecules.

00:02:40.350 --> 00:02:45.350
One, two, three, four, five, six, seven, eight, nine, ten.

00:02:45.648 --> 00:02:50.640
One, two, three, four, five, six, seven, eight, nine, ten.

00:02:51.030 --> 00:02:52.760
And let's say we know that the

00:02:52.760 --> 00:02:55.210
temperature here is 300 Kelvin.

00:02:56.440 --> 00:02:58.940
So the temperature of this system is 300 Kelvin.

00:02:58.940 --> 00:03:01.500
And the temperature of this system is 200 Kelvin.

00:03:02.040 --> 00:03:05.900
So if I wanted to visualize what these molecules are doing

00:03:05.900 --> 00:03:07.450
they're all moving around, they're bumping

00:03:07.450 --> 00:03:10.200
they don't all move together in unison.

00:03:10.540 --> 00:03:12.810
The average kinetic energy of the molecules

00:03:12.810 --> 00:03:15.010
in this system is going to be higher.

00:03:15.010 --> 00:03:16.440
And so maybe you have

00:03:16.440 --> 00:03:18.965
this molecule is moving in that direction.

00:03:18.965 --> 00:03:20.830
So that's its velocity.

00:03:20.830 --> 00:03:22.610
This one has this velocity.

00:03:22.610 --> 00:03:23.770
This one's going there.

00:03:23.770 --> 00:03:25.800
This one might not be moving much at all.

00:03:25.800 --> 00:03:28.100
This one might be going really fast that way.

00:03:28.100 --> 00:03:30.340
This one might be going super fast that way.

00:03:30.340 --> 00:03:32.040
This is doing that.

00:03:32.270 --> 00:03:33.416
This is doing that.

00:03:33.712 --> 00:03:35.130
This is doing that.

00:03:35.132 --> 00:03:37.200
So if you were to now compare it to this system

00:03:37.200 --> 00:03:40.750
this system, you could still have a molecule

00:03:40.750 --> 00:03:41.800
that is going really fast.

00:03:41.800 --> 00:03:43.060
Maybe this molecule is going faster

00:03:43.060 --> 00:03:44.800
than any of the molecules over here.

00:03:44.800 --> 00:03:46.840
But on average, the molecules here

00:03:46.840 --> 00:03:48.730
have a lower kinetic energy.

00:03:48.730 --> 00:03:50.780
So this one maybe is doing this.

00:03:50.780 --> 00:03:52.750
I'm going to see if I can draw...

00:03:52.750 --> 00:03:56.520
On average, they're going to have a lower kinetic energy.

00:03:56.520 --> 00:03:58.110
That doesn't mean all of these molecules

00:03:58.110 --> 00:04:00.110
are necessarily slower than all of these molecules

00:04:00.110 --> 00:04:02.160
or have lower kinetic energy than all of these molecules.

00:04:02.160 --> 00:04:06.901
But on average they're going to have less kinetic energy.

00:04:06.901 --> 00:04:08.930
And we can actually draw a distribution.

00:04:08.930 --> 00:04:10.600
And this distribution, that is

00:04:10.600 --> 00:04:13.382
the Maxwell-Boltzmann distribution.

00:04:13.382 --> 00:04:15.110
So if we...

00:04:15.110 --> 00:04:18.350
Let me draw a little coordinate plane here.

00:04:18.850 --> 00:04:23.850
So let me draw a coordinate plane.

00:04:24.260 --> 00:04:28.160
So, if on this axis, I were to put speed.

00:04:28.670 --> 00:04:30.140
If I were to put speed.

00:04:30.140 --> 00:04:33.532
And on this axis, I would put number of molecules.

00:04:33.532 --> 00:04:38.340
Number of molecules.

00:04:38.690 --> 00:04:39.931
Right over here.

00:04:39.931 --> 00:04:43.310
For this system, the system that is at 300 Kelvin

00:04:43.310 --> 00:04:46.092
the distribution might look like this.

00:04:46.092 --> 00:04:47.831
So it might look

00:04:47.831 --> 00:04:48.910
the distribution...

00:04:48.910 --> 00:04:50.340
Let me do this in a new color.

00:04:50.690 --> 00:04:53.120
So, the distribution

00:04:53.120 --> 00:04:54.840
this is gonna be all of the molecules.

00:04:54.840 --> 00:04:59.330
The distribution might look like this.

00:04:59.700 --> 00:05:00.890
Might look like this.

00:05:00.890 --> 00:05:02.920
And this would actually be the Maxwell-Boltzmann

00:05:02.920 --> 00:05:05.172
distribution for this system

00:05:05.172 --> 00:05:07.928
For system, let's call this system A.

00:05:07.928 --> 00:05:10.428
System A, right over here.

00:05:10.428 --> 00:05:14.710
And this system, that has a lower temperature

00:05:14.710 --> 00:05:17.238
which means it also has a lower kinetic energy.

00:05:17.238 --> 00:05:19.676
The distribution of its particles...

00:05:19.676 --> 00:05:22.615
So the most likely, the most probable...

00:05:22.615 --> 00:05:24.710
You're going to have the highest number of molecules

00:05:24.710 --> 00:05:25.900
at a slower speed.

00:05:25.900 --> 00:05:27.330
Let's say you're gonna have it at this speed

00:05:27.330 --> 00:05:28.603
right over here.

00:05:28.603 --> 00:05:33.600
So its distribution might look something like this.

00:05:35.000 --> 00:05:37.010
So it might look something like that.

00:05:37.740 --> 00:05:38.980
Now why is this one...

00:05:38.980 --> 00:05:40.310
It might make sense to you that

00:05:40.310 --> 00:05:42.020
okay, the most probable

00:05:42.020 --> 00:05:45.500
the speed at which I have the most molecules

00:05:45.500 --> 00:05:48.460
I get that that's going to be lower than the speed

00:05:48.460 --> 00:05:51.310
at which I have the most molecules in system A

00:05:51.310 --> 00:05:54.280
because I have, because on average

00:05:54.280 --> 00:05:56.050
these things have less kinetic energy.

00:05:56.050 --> 00:05:58.235
They're going to have less speed.

00:05:58.235 --> 00:06:00.184
But why is this peak higher?

00:06:00.184 --> 00:06:01.550
Well, you gotta remember we're talking about

00:06:01.550 --> 00:06:03.080
the same number of molecules.

00:06:03.080 --> 00:06:05.350
So if we have the same number of molecules that means

00:06:05.350 --> 00:06:07.910
that the areas under these curves need to be the same.

00:06:07.910 --> 00:06:10.900
So if this one is narrower, it's going to be taller.

00:06:10.900 --> 00:06:12.760
And if I were gonna, if I were to somehow

00:06:12.760 --> 00:06:15.380
raise the temperature of this system even more.

00:06:15.380 --> 00:06:17.780
Let's say I create a third system or I get this

00:06:17.780 --> 00:06:20.020
or let's say I were to heat it up to 400 Kelvin.

00:06:20.020 --> 00:06:24.120
Well then my distribution would look

00:06:24.120 --> 00:06:27.470
something like this.

00:06:27.470 --> 00:06:29.940
So this is if I heated it up.

00:06:30.270 --> 00:06:32.800
Heated up.

00:06:32.800 --> 00:06:35.620
And so this is all the Maxwell-Boltzmann distribution is.

00:06:35.620 --> 00:06:39.800
I'm not giving you the more involved, hairy equation for it

00:06:39.800 --> 00:06:42.128
but really the idea of what it is.

00:06:42.128 --> 00:06:43.530
It's a pretty neat idea.

00:06:43.530 --> 00:06:46.010
And actually when you actually think about the actual

00:06:46.010 --> 00:06:49.690
speeds of some of these particles, even the air around you

00:06:49.690 --> 00:06:52.060
I'm gonna say, "Oh, it looks pretty stationary to me."

00:06:52.060 --> 00:06:54.700
But it turns out in the air around you is mostly nitrogen.

00:06:54.700 --> 00:06:59.000
That the most probable speed of

00:06:59.000 --> 00:07:00.410
if you picked a random nitrogen

00:07:00.410 --> 00:07:02.618
molecule around you right now.

00:07:02.618 --> 00:07:04.340
So the most probable speed.

00:07:04.340 --> 00:07:05.160
I'm gonna write this down

00:07:05.160 --> 00:07:07.039
'cause this is pretty mindblowing.

00:07:07.039 --> 00:07:10.780
Most probable speed at room temperature.

00:07:10.784 --> 00:07:15.780
Probable speed

00:07:16.197 --> 00:07:20.154
of N2 at room temperature.

00:07:20.154 --> 00:07:23.960
Room temperature.

00:07:25.230 --> 00:07:27.400
So let's say this that this was the Maxwell-Boltzmann

00:07:27.400 --> 00:07:30.960
distribution for nitrogen at room temperature.

00:07:30.960 --> 00:07:32.620
Let's say that that's, let's say we make

00:07:32.620 --> 00:07:35.450
we call room temperature 300 Kelvin.

00:07:35.450 --> 00:07:37.870
This most probable speed right over here

00:07:37.870 --> 00:07:40.030
the one where we have the most molecules

00:07:40.030 --> 00:07:41.400
the one where we're gonna have the most

00:07:41.400 --> 00:07:43.070
molecules at that speed.

00:07:43.630 --> 00:07:45.990
In fact, guess what that is going to be before I tell you

00:07:45.990 --> 00:07:47.635
'cause it's actually mind boggling.

00:07:47.635 --> 00:07:49.930
Well, it turns out that it is approximately

00:07:49.930 --> 00:07:53.690
400, 400 and actually at 300 Kelvin

00:07:53.690 --> 00:07:57.846
it's gonna be 422 meters per second.

00:07:57.846 --> 00:08:00.510
422 meters per second.

00:08:00.510 --> 00:08:04.220
Imagine something traveling 422 meters in a second.

00:08:04.220 --> 00:08:06.700
And if you're used to thinking in terms of miles per hour

00:08:06.700 --> 00:08:09.860
this is approximately 944

00:08:09.860 --> 00:08:12.730
miles per hour.

00:08:12.730 --> 00:08:14.927
So right now, around you

00:08:14.927 --> 00:08:16.850
you have, actually

00:08:16.850 --> 00:08:20.340
the most probable, the highest number

00:08:20.340 --> 00:08:22.300
of the nitrogen molecules around you

00:08:22.300 --> 00:08:24.900
are traveling at roughly this speed

00:08:24.900 --> 00:08:26.280
and they're bumping into you.

00:08:26.280 --> 00:08:27.860
That's actually what's giving you air pressure.

00:08:27.860 --> 00:08:29.480
And not just that speed, there are actually ones

00:08:29.480 --> 00:08:31.190
that are travelling even faster than that.

00:08:31.190 --> 00:08:34.570
Even faster than 422 meters per second.

00:08:34.570 --> 00:08:35.210
Even faster.

00:08:35.210 --> 00:08:37.730
There's particles around you traveling faster

00:08:37.730 --> 00:08:39.210
than a thousand miles per hour

00:08:39.210 --> 00:08:41.980
and they are bumping into your body as we speak.

00:08:41.980 --> 00:08:43.650
And you might say, "Well, why doesn't that hurt?"

00:08:43.650 --> 00:08:47.040
Well, that gives you a sense of how small the mass

00:08:47.040 --> 00:08:48.870
of a nitrogen molecule is, that it can

00:08:48.870 --> 00:08:51.640
bump into you at a thousand miles per hour

00:08:51.640 --> 00:08:52.640
and you really don't feel it.

00:08:52.640 --> 00:08:55.554
It feels just like the ambient air pressure.

00:08:55.554 --> 00:08:57.030
Now, when you first look at this, you're like

00:08:57.030 --> 00:08:59.300
wait, 422 meters per second?

00:08:59.300 --> 00:09:01.510
That's faster than the speed of sound.

00:09:01.510 --> 00:09:04.770
The speed of sound is around 340 meters per second.

00:09:04.770 --> 00:09:06.000
Well, how can this be?

00:09:06.000 --> 00:09:06.860
Well, just think about it.

00:09:06.860 --> 00:09:09.220
Sound is transmitted through the air

00:09:09.220 --> 00:09:10.970
through collisions of particles.

00:09:10.970 --> 00:09:13.420
So the particles themselves have to be moving

00:09:13.420 --> 00:09:15.300
or at least some of them, have to be moving

00:09:15.300 --> 00:09:16.780
faster than the speed of sound.

00:09:16.780 --> 00:09:18.960
So, not all of the things around you

00:09:18.960 --> 00:09:19.910
are moving this fast and they're

00:09:19.910 --> 00:09:20.810
moving in all different directions.

00:09:20.810 --> 00:09:23.298
Some of them might not be moving much at all.

00:09:23.298 --> 00:09:26.520
But some of them are moving quite incredibly fast.

00:09:26.520 --> 00:09:28.800
So, I don't know, I find that a little bit mindblowing.


Prokaryotic and eukaryotic cells

WEBVTT
Kind: captions
Language: en

00:00:00.000 --> 00:00:01.859
- [Voiceover] When we wanna categorize life

00:00:01.859 --> 00:00:03.680
as we know it at a very high level,

00:00:03.680 --> 00:00:07.120
we can categorize it as either eukaryotic,

00:00:07.140 --> 00:00:11.800
eukaryotic or as a eukaryote,

00:00:11.800 --> 00:00:16.340
eukaryote, or as a prokaryote,

00:00:18.120 --> 00:00:20.260
prokaryote.

00:00:20.260 --> 00:00:24.040
And the largest distinction between a eukaryote and a

00:00:24.040 --> 00:00:26.940
prokaryote are membrane-bound structures

00:00:26.940 --> 00:00:31.240
that eukaryotes have that prokaryotes don't have.

00:00:31.240 --> 00:00:35.320
The most noticeable of which is a membrane-bound nucleus.

00:00:35.320 --> 00:00:38.500
So in a eukaryote, the genetic information is going to be

00:00:38.500 --> 00:00:41.660
inside a membrane-bound nucleus.

00:00:41.660 --> 00:00:46.140
So this right over here, this is the nucleus.

00:00:46.140 --> 00:00:48.270
This is the nucleus and you have your genetic

00:00:48.270 --> 00:00:50.680
information inside it, you have your DNA.

00:00:50.680 --> 00:00:53.610
Here, for a prokaryotic cell, you're going to have your DNA.

00:00:53.610 --> 00:00:55.680
It might be bundled up into a section of the cell.

00:00:55.680 --> 00:00:59.800
We would call that a nucleoid but it's not membrane-bound.

00:00:59.800 --> 00:01:01.020
So let me we write this down

00:01:01.020 --> 00:01:03.949
no membrane...

00:01:07.540 --> 00:01:11.050
Let me write a little membrane-bound,

00:01:11.050 --> 00:01:15.020
membrane-bound nucleus.

00:01:15.020 --> 00:01:19.000
But that's not the only distinction in between

00:01:19.000 --> 00:01:21.140
eukaryotes and prokaryotes.

00:01:21.140 --> 00:01:22.800
It's almost the one that's most noted.

00:01:22.800 --> 00:01:26.060
In fact, the word eukaryote, the karyote part

00:01:26.060 --> 00:01:29.380
comes from the Greek for nut or kernel.

00:01:29.380 --> 00:01:31.340
So let me make this clear.

00:01:31.340 --> 00:01:35.320
So this is referring to a nut

00:01:37.260 --> 00:01:41.370
or a kernel

00:01:41.370 --> 00:01:45.040
while prokaryote means before the nut or kernel.

00:01:45.040 --> 00:01:46.980
So we don't see and you know, I just could think of the

00:01:46.980 --> 00:01:49.640
nut or the kernel as the membrane-bound structure,

00:01:49.640 --> 00:01:52.240
especially the membrane-bound nucleus over here.

00:01:52.240 --> 00:01:53.100
But that's not all.

00:01:53.100 --> 00:01:56.300
Eukaryotes will also have other membrane-bound structures

00:01:56.300 --> 00:01:58.400
that you will not see in prokaryotes.

00:01:58.400 --> 00:02:01.540
For example, you will tend to see mitochondria,

00:02:03.800 --> 00:02:06.160
mitochondria,

00:02:06.160 --> 00:02:10.200
in a eukaryotic cell, both plant and animal cells,

00:02:10.200 --> 00:02:13.100
but you won't see it in a prokaryotic cell.

00:02:13.100 --> 00:02:15.940
And there's other types of membrane-bound structures.

00:02:15.940 --> 00:02:18.620
You could see things like Golgi apparatus.

00:02:18.620 --> 00:02:21.780
This over here is a micrograph of a eukaryotic cell.

00:02:21.780 --> 00:02:24.100
And you see the Golgi apparatus, right over here,

00:02:24.100 --> 00:02:26.410
which helps package proteins.

00:02:26.410 --> 00:02:28.700
You see a micrograph of mitrochondria.

00:02:28.700 --> 00:02:30.640
This is a micrograph of the nucleus.

00:02:30.640 --> 00:02:34.720
So this, right over here, is the nuclear membrane.

00:02:34.720 --> 00:02:36.540
And then you see all the genetic information.

00:02:36.540 --> 00:02:37.320
It's all spread out.

00:02:37.320 --> 00:02:39.130
It's in chromatin form right over here but you see

00:02:39.130 --> 00:02:41.620
it's especially densely packed right over here.

00:02:41.620 --> 00:02:43.960
And we've also put it in this and right over there.

00:02:43.960 --> 00:02:46.060
So this is all the DNA in chromatin form

00:02:46.060 --> 00:02:48.990
but this part that looks extra dense or dark

00:02:48.990 --> 00:02:50.590
in this micrograph right over there,

00:02:50.590 --> 00:02:53.290
we call that the nucleolus.

00:02:53.290 --> 00:02:57.680
We call that the nucleolus.

00:02:57.680 --> 00:02:59.240
And we now know that this is where

00:02:59.260 --> 00:03:02.780
ribosomal RNA is being produced.

00:03:02.780 --> 00:03:06.800
And ribosomal RNA, that forms part of the structure

00:03:06.800 --> 00:03:09.980
of ribosomes which are essential in the translation,

00:03:09.980 --> 00:03:12.200
well I guess you can say, the construction of proteins

00:03:12.200 --> 00:03:14.040
based on the information in mRNA.

00:03:14.040 --> 00:03:16.880
We'll go into a lot more depth in that in other videos.

00:03:16.880 --> 00:03:19.680
So these are ribosomes right over here

00:03:19.680 --> 00:03:22.200
and they're made up of ribosomal RNA

00:03:22.200 --> 00:03:24.440
and they're also made up of proteins.

00:03:24.440 --> 00:03:27.340
And so this nucleolus over there, that's where

00:03:27.360 --> 00:03:30.580
that's happening, that denser part of the nucleus.

00:03:30.580 --> 00:03:33.960
So the key distinction, eukaryotic cell,

00:03:33.960 --> 00:03:37.840
you have a membrane-bounded nucleus,

00:03:37.840 --> 00:03:41.720
you have other membrane-bound structures like mitochondria.

00:03:41.720 --> 00:03:43.100
In fact, there's some theories that

00:03:43.100 --> 00:03:47.560
mitochondria first evolved as prokaryotic organisms

00:03:47.560 --> 00:03:49.210
that eventually lived in symbiosis

00:03:49.210 --> 00:03:53.640
inside of a larger eukaryotic cell.

00:03:53.640 --> 00:03:56.880
And then the other distinction is that in eukaryotes,

00:03:56.880 --> 00:04:00.000
the DNA tends to be in multiple strands.

00:04:00.000 --> 00:04:02.760
So the DNA, if you were to kinda straighten it out,

00:04:02.760 --> 00:04:04.660
it would be in multiple strands.

00:04:04.660 --> 00:04:09.360
On a prokaryote, the DNA tends to be circular.

00:04:09.360 --> 00:04:12.180
It can be all flipped around and whatever else

00:04:12.180 --> 00:04:15.230
but at the end of the day, it would be circular DNA.

00:04:15.230 --> 00:04:17.070
So those are the three core distinctions:

00:04:17.070 --> 00:04:19.889
nuclear membrane, other membrane-bound organelles,

00:04:19.889 --> 00:04:24.120
like mitochondria and the Golgi apparatus,

00:04:24.120 --> 00:04:27.760
and then you also have multiple single strands of DNA

00:04:27.760 --> 00:04:29.860
versus circular DNA.

00:04:29.860 --> 00:04:32.880
Other things is that eukaryotes tend to be larger,

00:04:32.880 --> 00:04:35.820
while prokaryotes tend to be smaller, they tend to be simpler.

00:04:35.820 --> 00:04:37.500
So now that we know the key distinctions,

00:04:37.500 --> 00:04:40.140
what are examples of eukaryotes?

00:04:40.140 --> 00:04:42.200
Well, eukaryotes include most of

00:04:42.200 --> 00:04:44.290
what we interact with on a daily basis

00:04:44.290 --> 00:04:46.650
or we think we're interacting with on a daily basis.

00:04:46.650 --> 00:04:50.110
These includes all multicellular organisms,

00:04:50.110 --> 00:04:52.100
so multicellular,

00:04:52.100 --> 00:04:55.770
multicellular organisms.

00:04:55.770 --> 00:04:59.040
So I'm thinking animals, plants, fungi.

00:04:59.040 --> 00:05:00.320
It includes protists.

00:05:00.320 --> 00:05:02.300
This is a paramuseum right over here.

00:05:02.300 --> 00:05:03.340
This is eukaryotic.

00:05:03.340 --> 00:05:05.580
It's going to have a membrane-bound nucleus

00:05:05.580 --> 00:05:06.960
and other organelles.

00:05:06.960 --> 00:05:09.720
This right over here, these are onion root tip cells.

00:05:09.720 --> 00:05:11.000
So these are plant cells.

00:05:11.000 --> 00:05:12.550
And you could actually see it's been stained

00:05:12.550 --> 00:05:15.610
You can actually see the membrane-bound nucleus here.

00:05:15.610 --> 00:05:17.380
And this is actually a cool picture because you can see

00:05:17.380 --> 00:05:20.880
the cells at different stages of mitosis,

00:05:20.880 --> 00:05:22.200
which is interesting.

00:05:22.200 --> 00:05:24.260
Animal cells, the things that make you you,

00:05:24.260 --> 00:05:26.300
you are eukaryotic.

00:05:26.300 --> 00:05:28.320
So what is prokaryotic?

00:05:28.320 --> 00:05:32.250
Well, bacteria is probably the most common example of that.

00:05:32.250 --> 00:05:34.340
Bacteria, right over here,

00:05:34.340 --> 00:05:37.540
these are prokaryotes.

00:05:37.540 --> 00:05:40.400
And the lesser talk or things that's

00:05:40.400 --> 00:05:43.100
talked about lot less is archaea.

00:05:43.100 --> 00:05:44.630
And archaea, people initially thought that

00:05:44.630 --> 00:05:47.000
these were a form of bacteria that just lived

00:05:47.000 --> 00:05:48.500
in vary extreme conditions.

00:05:48.500 --> 00:05:51.650
But now they know it's a completely different domain of life,

00:05:53.300 --> 00:05:56.260
archaea.

00:05:56.260 --> 00:05:58.670
And so when we think about the domains of life,

00:06:00.460 --> 00:06:03.150
the current thought is that you have bacteria here,

00:06:04.090 --> 00:06:08.180
bacteria here, you have archaea.

00:06:08.180 --> 00:06:11.020
You have archaea,

00:06:13.860 --> 00:06:16.000
And then you have,

00:06:16.000 --> 00:06:19.180
and then you have eukaryotes.

00:06:19.180 --> 00:06:23.210
I'll do it there, and then you have eukaryotes.

00:06:25.360 --> 00:06:27.050
And these are things that have all of

00:06:27.050 --> 00:06:28.520
the traits that we've talked about

00:06:28.520 --> 00:06:30.700
and so this include plants and animals

00:06:30.700 --> 00:06:33.260
and fungi and unicellular eukaryotes,

00:06:33.260 --> 00:06:35.160
protists, and things like that.

00:06:35.160 --> 00:06:37.540
And so, if we once again, just high level

00:06:37.540 --> 00:06:41.100
we would consider these prokaryotes

00:06:41.100 --> 00:06:44.560
and these of course are the eukaryotes.

00:06:44.560 --> 00:06:48.470
So hopefully that gives you a good overview of things.


Cell size

WEBVTT
Kind: captions
Language: en

00:00:00.395 --> 00:00:03.761
- What I want to think about in this video is cell size,

00:00:03.761 --> 00:00:07.314
and in particular how small cells can get, and then also

00:00:07.314 --> 00:00:09.798
what tends to be the limiting factors for how large

00:00:09.798 --> 00:00:11.424
a cell can get.

00:00:11.424 --> 00:00:14.187
And I have some pictures of cells here.

00:00:14.187 --> 00:00:16.718
This picture right over here, this picture

00:00:16.718 --> 00:00:20.224
of pseudomonas bacteria, each of these pill-shaped things,

00:00:20.224 --> 00:00:22.592
this is a bacterial cell.

00:00:22.592 --> 00:00:26.005
And just to get a sense of scale, the width of this pill

00:00:26.005 --> 00:00:28.048
is around one micrometer.

00:00:28.048 --> 00:00:32.228
So, this is approximately one micrometer, which is the same

00:00:32.228 --> 00:00:34.852
thing as 1 millionth of a meter.

00:00:34.852 --> 00:00:37.777
Or you could think of it as 1 thousandth of a milimeter,

00:00:37.777 --> 00:00:39.983
whatever helps you conceptualize this better.

00:00:39.983 --> 00:00:42.955
And then the length here, this is about 5 micrometers.

00:00:42.955 --> 00:00:46.949
This is approximately 5 micrometers.

00:00:46.949 --> 00:00:49.758
Now over here I have some pictures of cells that you would

00:00:49.758 --> 00:00:51.592
find in the human body, these are red blood cells.

00:00:51.592 --> 00:00:56.213
These have a diameter of about 7 micrometers.

00:00:56.213 --> 00:00:58.930
You see a similar scale for these white blood cells.

00:00:58.930 --> 00:01:00.625
There are some other things in here.

00:01:00.625 --> 00:01:03.690
Over here we see a human sperm cell about to penetrate

00:01:03.690 --> 00:01:06.638
a human egg cell, and human egg cells are some of

00:01:06.638 --> 00:01:09.680
the largest cells you'd find, especially if we're talking

00:01:09.680 --> 00:01:13.999
about spherical cells.

00:01:13.999 --> 00:01:16.112
And this cell here, this is going to have a diameter

00:01:16.112 --> 00:01:20.988
on the order of 100 micrometers.

00:01:20.988 --> 00:01:23.054
So the first question we would, and it's kind of neat that

00:01:23.054 --> 00:01:25.306
all of these pictures are almost on the same scale,

00:01:25.306 --> 00:01:28.998
so you can almost compare them, but the first question

00:01:28.998 --> 00:01:31.622
we'd ask is how small can a cell get?

00:01:31.622 --> 00:01:33.689
Well, if you think about it a cell is a living thing,

00:01:33.689 --> 00:01:35.384
it's actually quite complex.

00:01:35.384 --> 00:01:38.007
It has to have information, it has DNA, it has to be able

00:01:38.007 --> 00:01:41.351
to replicate itself, it has all of this metabolic machinery.

00:01:41.351 --> 00:01:46.273
So, I just did some reading and the smallest cells observed,

00:01:46.273 --> 00:01:49.036
and I think this might be the smallest cells period although

00:01:49.036 --> 00:01:51.869
there might be future ones discovered that are even smaller,

00:01:51.869 --> 00:01:54.934
are actually on the order of about a few 100 nanometers.

00:01:54.934 --> 00:01:58.695
Remember, 1,000 nanometers would be the width of this pill

00:01:58.695 --> 00:02:01.644
so a few 100 nanometers like maybe something like that

00:02:01.644 --> 00:02:05.870
would be maybe 300 nanometers, these are the smallest

00:02:05.870 --> 00:02:07.194
cells discovered so far.

00:02:07.194 --> 00:02:08.749
And they are bacterial cells, they were discovered at

00:02:08.749 --> 00:02:10.978
the University of California Berkeley.

00:02:10.978 --> 00:02:16.783
And we think that this is pretty close to the lower bound

00:02:16.783 --> 00:02:18.803
because you've got to remember we have to store all of

00:02:18.803 --> 00:02:22.216
this genetic information and all this cellular machinery.

00:02:22.216 --> 00:02:25.954
So, that stuff's complex and you can only get so small.

00:02:25.954 --> 00:02:28.392
But what about the upper bound cells?

00:02:28.392 --> 00:02:31.573
Well, one of the things that tends to be the limiting factor

00:02:31.573 --> 00:02:34.476
and there's other things as well, but it's the ability for,

00:02:34.476 --> 00:02:37.239
it's the ratio of volume to surface area.

00:02:37.239 --> 00:02:42.045
And why does the ratio of volume to surface area matter?

00:02:42.045 --> 00:02:44.623
Well, because the surface is what interfaces

00:02:44.623 --> 00:02:47.502
the cell with its surroundings.

00:02:47.502 --> 00:02:51.170
It has to take in nutrients and take out the waste,

00:02:51.170 --> 00:02:55.373
so each unit of surface area it has to process the inputs

00:02:55.373 --> 00:02:58.020
and the outputs for a certain volume of cells,

00:02:58.020 --> 00:03:00.481
for a certain volume of the cell.

00:03:00.481 --> 00:03:03.755
And as we'll see as a cell grows the volume and surface

00:03:03.755 --> 00:03:06.193
area don't grow together, the volume increases faster

00:03:06.193 --> 00:03:08.051
than the surface area does.

00:03:08.051 --> 00:03:11.023
So, as you grow, each unit of surface area has to handle

00:03:11.023 --> 00:03:13.182
the processing with the environment for more

00:03:13.182 --> 00:03:14.575
and more volume.

00:03:14.575 --> 00:03:17.408
At some point it can't handle it, it can't take in nutrients

00:03:17.408 --> 00:03:20.496
and get rid of waste fast enough.

00:03:20.496 --> 00:03:22.423
And to make that a little bit more tangible,

00:03:22.423 --> 00:03:24.257
let's think about it mathematically.

00:03:24.257 --> 00:03:28.692
So, the volume of a sphere, let's say this is a sphere here

00:03:28.692 --> 00:03:31.479
so let me make it look a little more 3-dimensional,

00:03:31.479 --> 00:03:38.258
if it has radius "r", its volume is going to be (4/3)πr³.

00:03:38.258 --> 00:03:46.246
Now, it's surface area is going to be 4πr².

00:03:46.246 --> 00:03:49.032
Now let's calculate the ratio of volume to surface area

00:03:49.032 --> 00:03:50.216
because that's what we really care about.

00:03:50.216 --> 00:03:54.140
The ratio of volume to surface area is, I want to do

00:03:54.140 --> 00:04:09.651
surface area in yellow, is equal to (4/3)πr³ over 4πr².

00:04:09.651 --> 00:04:11.787
Now, luckily this simplifies quite nicely.

00:04:11.787 --> 00:04:14.921
4 divided by 4 is 1, π divided by π is 1,

00:04:14.921 --> 00:04:17.893
r³ divided by r² is just going to be "r",

00:04:17.893 --> 00:04:22.560
so this all simplified nicely to r/3.

00:04:22.560 --> 00:04:24.766
And if we wanted to care about units, it would be cubic

00:04:24.766 --> 00:04:27.343
units of volume or it would be cubic units divided by

00:04:27.343 --> 00:04:31.662
square units, whichever unit we're looking at.

00:04:31.662 --> 00:04:33.822
So this is going to be r/3.

00:04:33.822 --> 00:04:36.701
So, let's use this to think about what happens

00:04:36.701 --> 00:04:40.160
as a cell gets much larger.

00:04:40.160 --> 00:04:44.618
So for simplicity, let's focus on this white blood cell here

00:04:44.618 --> 00:04:47.126
and just to make the math easy let's assume that it has

00:04:47.126 --> 00:04:53.302
a radius of 3 micrometers.

00:04:53.302 --> 00:04:56.251
I'm gonna do this in a color you can see, 3 micrometers.

00:04:56.251 --> 00:04:59.827
So in that case, for this cell, its volume to surface area

00:04:59.827 --> 00:05:05.237
is going to be, we could just say 3 micrometers divided by 3

00:05:05.237 --> 00:05:12.528
but I'll put 3 micrometers divided by 3, which of course is

00:05:12.528 --> 00:05:14.849
just going to be 1 micrometer.

00:05:14.849 --> 00:05:17.264
But having a unit of 1 micrometer for volume of surface area

00:05:17.264 --> 00:05:18.774
doesn't really make a lot of sense.

00:05:18.774 --> 00:05:25.461
An equivalent unit would say 1 cubic micrometer per

00:05:25.461 --> 00:05:29.895
square micrometer, because we're doing volume to

00:05:29.895 --> 00:05:32.101
surface area and obviously if you let the units cancel and

00:05:32.101 --> 00:05:33.936
you do the dimensional analysis you'd be just left with

00:05:33.936 --> 00:05:35.259
this micrometer.

00:05:35.259 --> 00:05:37.743
But this helps us conceptualize a little bit more because

00:05:37.743 --> 00:05:41.226
it says that each square micrometer needs to handle

00:05:41.226 --> 00:05:44.547
one cubic micrometer of cellular volume.

00:05:44.547 --> 00:05:47.519
So each square micrometer, so the square micrometer for

00:05:47.519 --> 00:05:50.514
this guy over here is gonna be around that size,

00:05:50.514 --> 00:05:53.532
it's going to handle the processing on average for

00:05:53.532 --> 00:05:57.363
1 cubic micrometer of volume.

00:05:57.363 --> 00:05:59.662
Alright, that seems about reasonable and that's a reasonable

00:05:59.662 --> 00:06:01.357
size for a cell.

00:06:01.357 --> 00:06:06.233
But what if we were to increase things by a factor of 1,000

00:06:06.233 --> 00:06:08.625
or increase the radius by a factor of 1,000?

00:06:08.625 --> 00:06:11.272
So I'm obviously not drawing this to scale, but let's say

00:06:11.272 --> 00:06:14.592
we find some new organism or we theorize some organism

00:06:14.592 --> 00:06:19.352
thats cellular radius, instead of being 3 micrometers,

00:06:19.352 --> 00:06:25.180
so this was 3 micrometers, it's 3,000 millionths of a meter.

00:06:25.180 --> 00:06:27.734
And just to be clear this isn't ginormous, by our scales

00:06:27.734 --> 00:06:30.590
this would be 3 millimeters.

00:06:30.590 --> 00:06:33.539
It would be visible by the human eye, the threshold of the

00:06:33.539 --> 00:06:35.953
human eye can see is about a tenth of a millimeter,

00:06:35.953 --> 00:06:37.834
which is 100 micrometers.

00:06:37.834 --> 00:06:41.828
This is approximately 1/10 of a millimeter.

00:06:41.828 --> 00:06:43.732
So on the right conditions you can just barely see

00:06:43.732 --> 00:06:46.681
a human egg cell, but this right over here, this would be

00:06:46.681 --> 00:06:49.258
still small by our scales, but let's just think about what

00:06:49.258 --> 00:06:53.159
happens to the volume to surface area.

00:06:53.159 --> 00:07:01.866
3,000 micrometers divided by 3, we'd be left with

00:07:01.866 --> 00:07:04.652
1,000 micrometers, or even better we could write this as

00:07:04.652 --> 00:07:11.223
1,000 cubic micrometers per square micrometer.

00:07:11.223 --> 00:07:14.079
So now, each square micrometer, in this case it had to

00:07:14.079 --> 00:07:17.074
handle a cubic micrometer of volume.

00:07:17.074 --> 00:07:22.066
But now it has to handle 1,000 cubic micrometers of volume.

00:07:22.066 --> 00:07:25.642
So it has to handle much more volume.

00:07:25.642 --> 00:07:27.523
And that's gonna break down, it's not gonna be able

00:07:27.523 --> 00:07:30.425
to exchange the gasses, exchange the nutrients,

00:07:30.425 --> 00:07:33.815
exchange the waste fast enough for this cell to function.

00:07:33.815 --> 00:07:38.134
So this is a very important ratio, volume to surface area

00:07:38.134 --> 00:07:40.734
for cells, and actually ends up, well I'll just talk

00:07:40.734 --> 00:07:42.987
about cells in general.

00:07:42.987 --> 00:07:45.448
It actually tends to be an interesting thing as a lot

00:07:45.448 --> 00:07:50.161
of things grow, volume to surface area or mass or there's

00:07:50.161 --> 00:07:51.624
a lot of other ratios that are interesting,

00:07:51.624 --> 00:07:52.785
but this is one of them.

00:07:52.785 --> 00:07:55.618
Now, the other factor that will play in is also as a cell

00:07:55.618 --> 00:07:57.847
gets larger, the machinery has to just traverse more

00:07:57.847 --> 00:07:59.612
distances, you have to transport things

00:07:59.612 --> 00:08:02.978
over larger distances which also can become cumbersome.

00:08:02.978 --> 00:08:05.045
But the volume to surface area is a really interesting one

00:08:05.045 --> 00:08:06.600
to think about, while we don't tend to see

00:08:06.600 --> 00:08:09.805
very large spherical cells.

00:08:09.805 --> 00:08:11.616
And the reason why I emphasize spherical cells is because

00:08:11.616 --> 00:08:15.354
you do see cells that are longer than even this scale,

00:08:15.354 --> 00:08:17.165
like nerve cells.

00:08:17.165 --> 00:08:19.719
And they get by with that, they have other adaptations.

00:08:19.719 --> 00:08:23.179
But one of them is to just be really skinny and long,

00:08:23.179 --> 00:08:25.872
so this is one way that they can maximize

00:08:25.872 --> 00:08:28.357
their surface area.

00:08:28.357 --> 00:08:32.118
So, like that, this is a nerve cell.

00:08:32.118 --> 00:08:34.185
Other ways that you'll see cells that maximize their

00:08:34.185 --> 00:08:35.949
surface area is that they have a lot of things that kind of

00:08:35.949 --> 00:08:38.225
stick out to maximize.

00:08:38.225 --> 00:08:41.568
So, cells are clearly not all spherical.

00:08:41.568 --> 00:08:43.728
So, they could have other things that maximize their

00:08:43.728 --> 00:08:45.237
surface area like that.

00:08:45.237 --> 00:08:47.419
So there's a bunch of adaptations, but in general, modeling

00:08:47.419 --> 00:08:49.927
them as a sphere isn't a crazy thing to do and this is why

00:08:49.927 --> 00:08:52.388
we don't tend to see cells much larger

00:08:52.388 --> 00:08:54.496
than a human egg cell.


Cell theory

WEBVTT
Kind: captions
Language: en

00:00:00.000 --> 00:00:03.960
To us modern folk, we tend to take for granted the existence of cells

00:00:03.960 --> 00:00:06.500
and the idea that all living things are made up of cells

00:00:07.000 --> 00:00:11.000
that we as human beings, as living organisms, we are made up of many, many, many cells

00:00:11.220 --> 00:00:19.380
the estimates of the cells, of the human body, are around the order of 37 trillion cells!

00:00:19.440 --> 00:00:23.200
But, if we were to rewind, even 400 years ago to the 1600's

00:00:23.260 --> 00:00:25.000
this wasn't so obvious.

00:00:25.000 --> 00:00:26.920
and that is because people really didn't have the tools

00:00:26.920 --> 00:00:30.960
to make direct observations of cells. They didn't know that these cells were around.

00:00:30.960 --> 00:00:34.040
They didn't know that things, even like unicellular organisms, even existed!

00:00:34.540 --> 00:00:37.340
But, all of that began to change, with Robert Hooke.

00:00:38.920 --> 00:00:43.500
Robert Hooke, was able to leverage a primitive microscope

00:00:43.560 --> 00:00:45.400
and this is a picture of his microscope

00:00:45.400 --> 00:00:46.980
and when you see this, you appreciate how

00:00:47.000 --> 00:00:48.720
at least relative, to what we have today, how primitive it was.

00:00:48.720 --> 00:00:51.660
He had lenses here, that would provide some magnification,

00:00:51.660 --> 00:00:56.280
but he had to use -- this right over here -- this is a flame, and he is able to channel that light

00:00:56.280 --> 00:00:59.420
so that it gets reflected over whatever he is observing.

00:00:59.420 --> 00:01:03.840
And in, 1665, he publishes the "Micrographia".

00:01:03.840 --> 00:01:07.340
I am probably not pronouncing it right.

00:01:07.340 --> 00:01:11.740
So, this is 1665, Robert Hooke publishes this

00:01:11.780 --> 00:01:14.760
and in this, he describes and he draws a lot

00:01:14.760 --> 00:01:18.680
of his observations, using his microscope.

00:01:18.680 --> 00:01:21.320
He has some fascinating drawings,  he was actually quite a good artist,

00:01:21.320 --> 00:01:23.720
where he was able to draw pictures

00:01:23.720 --> 00:01:26.940
of his observations, of things like lice, and fleas.

00:01:26.940 --> 00:01:30.580
But, it's not just lice and fleas that he is able to observe.

00:01:30.580 --> 00:01:36.880
He actually takes a look at some corks or what he just sees as "cork"

00:01:36.880 --> 00:01:49.160
and when he makes that observation, he says, "Hey look, you know there are these little squares over here, and this kind of seems to be somehow kind of a basic unit of this cork. "

00:01:49.160 --> 00:01:56.160
And he says, " Well, this kinda reminds me of these little rooms that monks live in and spend their time in, which we call cells".

00:01:56.160 --> 00:01:58.040
So he calls these cells.

00:01:58.040 --> 00:02:00.220
And, that is where the word comes from.

00:02:00.280 --> 00:02:02.060
He calls them cells, in "Micrographia".

00:02:03.100 --> 00:02:04.020
That is a cell.

00:02:04.020 --> 00:02:07.140
Now unfortunately for us, he was a great artist

00:02:07.140 --> 00:02:09.780
and he was really good at drawing things

00:02:09.780 --> 00:02:13.580
and he drew a lot in his "Micrographia", but we don't have any pictures of Robert Hooke anymore.

00:02:13.580 --> 00:02:16.880
And it's a fascinating story. Most theories are that

00:02:17.080 --> 00:02:22.920
actually,  it was Isaac Newton, who burned the only original painting, that we have of Robert Hooke.

00:02:22.920 --> 00:02:26.320
And, that is another intriguing story, that we can talk about, at a future date.

00:02:26.320 --> 00:02:31.800
But, what Robert Hooke — he coined these things "cells" — but he was looking at dead tissue, and actually he was

00:02:31.800 --> 00:02:37.040
looking at the remnants of cells. And what he saw was really just the cell wall remnants.

00:02:37.040 --> 00:02:41.920
He wasn't actually able to observe, directly,  "living cells". And he didn't have enough to go on

00:02:41.920 --> 00:02:46.140
to think , "Hey maybe, this is a building block of all life and maybe, cells themselves reproduce."

00:02:46.140 --> 00:02:52.520
"And, all cells come from other cells. "  And that doesn't start to get developed, until we get further on into history.

00:02:52.620 --> 00:02:57.320
You go a few years later, we get to Antonie von Leeuwenhoek.

00:02:57.320 --> 00:02:59.320
I know I'm not probably pronouncing it right.

00:03:00.280 --> 00:03:03.640
But he was a Dutch lense crafter, and he was inspired

00:03:03.640 --> 00:03:09.940
by Hooke's work , and he says "Hey, I can craft lenses, maybe I can use that to make better microscopes, and make better observations. "

00:03:10.120 --> 00:03:13.240
And he was able to do that, and doing that he was able to directly observe

00:03:13.240 --> 00:03:17.040
living cells and living unicellular organisms.

00:03:17.040 --> 00:03:19.920
So, he was able to directly observe sperm.

00:03:19.920 --> 00:03:23.340
He said, "Hey this thing looks like it's alive!"

00:03:23.340 --> 00:03:30.960
He was able to directly observe protists — so these unicellular, eukaryotic...

00:03:31.060 --> 00:03:34.780
... they have cell walls, these things that look like unicellular animals.

00:03:34.780 --> 00:03:37.780
And he called them, actually, "animalcules".

00:03:41.320 --> 00:03:47.240
Saying, "Hey, look, these look like these little mini-animals going on here. "

00:03:47.300 --> 00:03:51.060
And so he started to say, well maybe this is some form of a basis of life, or at least started to say,

00:03:51.060 --> 00:03:54.300
at this very small scale, you actually have life.

00:03:55.140 --> 00:04:03.040
But, a fully, modern theory of the cell, doesn't really start to emerge until we get another 100-150 years, into the future.

00:04:03.140 --> 00:04:05.480
And, we get into the early 1800's.

00:04:05.840 --> 00:04:13.620
So, if we fast-forward, to the 1830's , these two gentlemen, Matthias Schleiden and Theodor Schwann, come into the picture.

00:04:13.620 --> 00:04:16.360
And, they are the one's that start laying the foundation

00:04:16.360 --> 00:04:19.240
of what we can call, "modern cell theory".

00:04:19.240 --> 00:04:22.320
So, modern cell theory

00:04:22.320 --> 00:04:26.720
And using their observations and kind of what they are able to deduce

00:04:26.720 --> 00:04:30.480
they said, "Hey maybe, all living things

00:04:30.480 --> 00:04:42.360
all life,  is composed of one or more cells."

00:04:42.360 --> 00:04:45.660
And today, we kind of take this for granted, but this wasn't obvious.

00:04:45.660 --> 00:04:51.600
It wasn't obvious that all things, that this was somehow a building block for life, one or more cells.

00:04:51.600 --> 00:04:54.100
And then, following that if all life is composed of one or more cells,

00:04:54.100 --> 00:04:58.740
you can also say, that a cell, is the basic unit of life.

00:04:58.740 --> 00:05:07.480
Cell is basic unit of life

00:05:07.480 --> 00:05:09.680
And these are strong statements, that all life, if you were to get down small enough,

00:05:09.680 --> 00:05:14.820
you are going to come to cells, living cells, that make up that life.

00:05:15.240 --> 00:05:20.840
Now, this isn't our full, complete cell theory and both of these gentlemen, they knew that cells could come from other cells.

00:05:20.900 --> 00:05:25.320
They were able to observe cells reproducing, but, it still

00:05:25.320 --> 00:05:30.820
was an open question, "Hey, maybe some cells come from other cells? While others, maybe they somehow get spontaneously created ....

00:05:30.820 --> 00:05:36.700
... if you have the right elements and the right amount of conditions. Maybe they somehow just emerge out of nothing. "

00:05:36.780 --> 00:05:46.580
And, it wasn't until this kind of third tenet of modern cell theory, it wasn't until the mid 1800's that we get our third tenet of modern cell theory that gets established.

00:05:46.580 --> 00:05:51.300
And this is this idea that all cells come from other cells.

00:05:51.300 --> 00:05:56.340
All cells from other cells

00:05:56.340 --> 00:05:59.960
And the real father of this idea, the one that really established this,

00:05:59.960 --> 00:06:02.800
is this gentleman, right here, Robert Remak.

00:06:02.800 --> 00:06:09.200
Now sometimes, the credit for this goes to, Rudolph Virchow, right over here, but it turns out that

00:06:09.380 --> 00:06:17.840
he plagiarized Remak's work, so it's really Remak who deserves the bulk of the credit

00:06:17.840 --> 00:06:20.060
for this tenant, that all cells come from other cells.

00:06:20.060 --> 00:06:23.980
And once again, he wasn't the first person to say, "Hey, maybe, we will observe that some cells..

00:06:23.980 --> 00:06:31.560
.. come from other cells." But he said, "This is a fundamental thing, all cells, this is how they actually come about  they aren't just somehow, spontaneously emerged".

00:06:31.560 --> 00:06:34.780
Now whenever, even in today's world, people

00:06:34.780 --> 00:06:37.020
see this last thing, all cells come from other cells,

00:06:37.020 --> 00:06:42.740
there is a natural question, " Well, there must have been a first cell or an initial set of "proto-cells ?".

00:06:43.100 --> 00:06:47.100
And, people aren't a hundred percent sure, but when we

00:06:47.100 --> 00:06:53.320
look back, at the evolution of life on earth, we think the first cells emerged about three and a half billion years ago.

00:06:53.320 --> 00:06:57.480
And we are not a hundred percent sure about how they emerged, but there are some theories.

00:06:57.560 --> 00:07:00.600
For example, we have videos on, phospholipids,

00:07:00.740 --> 00:07:09.460
and it turns out that, phospholipids, naturally form bi-layers

00:07:10.040 --> 00:07:15.500
and they can actually form, spherical membranes, that have phospholipid bi-layers.

00:07:15.500 --> 00:07:19.320
So, that kinda gets you a start, so that can spontaneously form.

00:07:19.320 --> 00:07:24.700
And, there is also, theories that maybe in the information, the machinery of cells

00:07:24.700 --> 00:07:28.520
maybe their ancestors, if we were to go three and a half billion years or longer ago,

00:07:28.520 --> 00:07:34.840
that it might have been self-replicating RNA molecules or maybe it was somehow, self-replicating proteins

00:07:34.840 --> 00:07:39.820
that over time, over very large, large time scales,

00:07:39.880 --> 00:07:44.820
were able to, start replicating themselves, have more sophisticated machinery,

00:07:44.960 --> 00:07:50.500
the ones that had or were approaching our modern cells, were able to reproduce more,

00:07:50.500 --> 00:07:54.340
were able to take advantage of more of the energy, the resources in an environment.

00:07:54.340 --> 00:08:00.540
So, that we eventually get to our modern cells. But, this is a fascinating question, and is still an area of research.


Scale of cells

WEBVTT
Kind: captions
Language: en

00:00:00.371 --> 00:00:02.927
- [Voiceover] When we study
science it's natural to

00:00:02.927 --> 00:00:05.245
just categorize a whole
series of things as just

00:00:05.245 --> 00:00:07.902
being really really unimaginably small.

00:00:07.902 --> 00:00:10.219
So when people say, hey atomic scale,

00:00:10.219 --> 00:00:11.571
or molecular scale,

00:00:11.571 --> 00:00:13.780
or protein, or cell,

00:00:13.780 --> 00:00:15.567
you often just group that together and say

00:00:15.567 --> 00:00:16.771
oh, those are really really really

00:00:16.771 --> 00:00:18.392
really small things.

00:00:18.392 --> 00:00:19.969
But what I want to do in this video

00:00:19.969 --> 00:00:21.695
is get an appreciation that even though

00:00:21.695 --> 00:00:23.951
all the things I've just
mentioned are really small,

00:00:23.951 --> 00:00:25.652
there's actually a huge difference

00:00:25.652 --> 00:00:27.387
in the sizes of those things.

00:00:27.387 --> 00:00:29.278
And hopefully that'll
give us an appreciation

00:00:29.278 --> 00:00:33.283
for how complex something
like a cell can be.

00:00:33.283 --> 00:00:35.141
How it can have all of this machinery.

00:00:35.141 --> 00:00:38.290
How it can actually be a living organism

00:00:38.290 --> 00:00:40.726
or part of a living organism.

00:00:40.726 --> 00:00:42.941
And so at this scale this is a

00:00:42.941 --> 00:00:44.416
this is my little rendering,

00:00:44.416 --> 00:00:46.032
my drawing of a water molecule.

00:00:46.032 --> 00:00:48.558
You have the oxygen atom
in the right over here

00:00:48.558 --> 00:00:49.558
in this purplish color,

00:00:49.558 --> 00:00:51.575
and then you have two hydrogen molecules

00:00:51.575 --> 00:00:52.639
bonded to it.

00:00:52.639 --> 00:00:54.375
And this is going to be roughly

00:00:54.375 --> 00:00:55.792
0.275 nanometers.

00:00:57.841 --> 00:00:59.240
And just to remind ourselves,

00:00:59.240 --> 00:01:01.556
a nanometer is a billionth

00:01:01.556 --> 00:01:02.623
of a meter.

00:01:02.623 --> 00:01:04.754
And just to get an appreciation of that

00:01:04.754 --> 00:01:05.750
so let me.

00:01:05.750 --> 00:01:06.960
So this is

00:01:06.960 --> 00:01:08.300
one billionth

00:01:08.300 --> 00:01:09.383
one billionth

00:01:11.055 --> 00:01:12.555
one billionth of a

00:01:14.752 --> 00:01:16.267
one billionth of a meter.

00:01:16.267 --> 00:01:17.470
That's a nanometer.

00:01:17.470 --> 00:01:18.805
And if you want to even attempt

00:01:18.805 --> 00:01:20.077
to visualize that

00:01:20.077 --> 00:01:22.211
that would be a millionth

00:01:22.211 --> 00:01:23.920
of a millimeter.

00:01:23.920 --> 00:01:26.458
So one, let me write this.

00:01:26.458 --> 00:01:27.875
One one millionth

00:01:29.404 --> 00:01:31.290
one millionth

00:01:31.290 --> 00:01:32.623
of a millimeter.

00:01:34.124 --> 00:01:35.771
And I actually like using this one

00:01:35.771 --> 00:01:37.770
because a millimeter is

00:01:37.770 --> 00:01:39.687
about as small as I can

00:01:40.670 --> 00:01:43.366
on a reasonable basis visualize.

00:01:43.366 --> 00:01:45.197
But instead of a millionth of that

00:01:45.197 --> 00:01:48.549
it goes well beyond, at
least my capabilities

00:01:48.549 --> 00:01:49.932
of visualization.

00:01:49.932 --> 00:01:51.677
So that would be the diameter

00:01:51.677 --> 00:01:54.697
or the width of a water molecule.

00:01:54.697 --> 00:01:56.191
But now let's go to the next scale up.

00:01:56.191 --> 00:01:57.847
We've talked a lot about proteins

00:01:57.847 --> 00:01:58.795
and this is our friend,

00:01:58.795 --> 00:02:00.727
this is right over here is

00:02:00.727 --> 00:02:03.130
our friend hemoglobin.

00:02:03.130 --> 00:02:04.652
And this gives you a sense of scale,

00:02:04.652 --> 00:02:06.590
the width of hemoglobin is going to be

00:02:06.590 --> 00:02:08.795
about five nanometers.

00:02:08.795 --> 00:02:11.295
Or five billionths of a meter.

00:02:12.249 --> 00:02:13.924
Now that seems super small,

00:02:13.924 --> 00:02:15.850
so in some ways it's okay to categorize

00:02:15.850 --> 00:02:18.181
that into your super
small part of the brain.

00:02:18.181 --> 00:02:19.108
But it's good to appreciate,

00:02:19.108 --> 00:02:21.462
this is much larger than a water molecule.

00:02:21.462 --> 00:02:23.693
If a water molecule were on this scale

00:02:23.693 --> 00:02:24.948
I predrew it, this little thing

00:02:24.948 --> 00:02:26.917
over here, that's my attempt

00:02:26.917 --> 00:02:28.876
at drawing a water molecule

00:02:28.876 --> 00:02:30.148
at this same scale.

00:02:30.148 --> 00:02:31.866
So even when you go from something

00:02:31.866 --> 00:02:34.094
like a water molecule to a protein

00:02:34.094 --> 00:02:36.576
you're already going
dramatically up in size

00:02:36.576 --> 00:02:38.180
and dramatically up in complexity.

00:02:38.180 --> 00:02:39.774
And we've talked a lot
about protein structure

00:02:39.774 --> 00:02:40.921
and how they can take on all of these

00:02:40.921 --> 00:02:42.889
interesting shapes, and do fairly

00:02:42.889 --> 00:02:44.976
surprising and complex things

00:02:44.976 --> 00:02:47.393
inside of biological systems.

00:02:48.650 --> 00:02:49.658
But now let's go,

00:02:49.658 --> 00:02:52.308
let's go the next scale up.

00:02:52.308 --> 00:02:53.513
And the next scale up

00:02:53.513 --> 00:02:55.327
I'm gonna go to a virus.

00:02:55.327 --> 00:02:57.056
And what I've attempted to draw here

00:02:57.056 --> 00:02:59.692
this is a fairly well known virus,

00:02:59.692 --> 00:03:01.456
this is HIV.

00:03:01.456 --> 00:03:03.241
And it's actually one
of the larger viruses

00:03:03.241 --> 00:03:04.645
and its diameter is roughly

00:03:04.645 --> 00:03:05.478
120,

00:03:06.766 --> 00:03:08.016
120 nanometers.

00:03:08.995 --> 00:03:10.536
So if we were to

00:03:10.536 --> 00:03:12.314
draw this hemoglobin

00:03:12.314 --> 00:03:14.500
this hemoglobin protein at the same scale

00:03:14.500 --> 00:03:15.834
as we've drawn this virus

00:03:15.834 --> 00:03:17.081
this thing right over here

00:03:17.081 --> 00:03:18.767
would be the hemoglobin protein.

00:03:18.767 --> 00:03:19.883
And we wouldn't even be able to see

00:03:19.883 --> 00:03:21.698
the water molecule at this scale

00:03:21.698 --> 00:03:23.322
right over here.

00:03:23.322 --> 00:03:25.530
But this is still really really small.

00:03:25.530 --> 00:03:27.937
This is 120 billionths

00:03:27.937 --> 00:03:29.470
of a meter.

00:03:29.470 --> 00:03:31.201
So this is still

00:03:31.201 --> 00:03:33.951
this is still unimaginably small.

00:03:34.877 --> 00:03:36.094
But now let's go up to the,

00:03:36.094 --> 00:03:37.648
let's go up to the next scale.

00:03:37.648 --> 00:03:39.330
So this creepy picture

00:03:39.330 --> 00:03:40.547
right over here,

00:03:40.547 --> 00:03:41.958
this is a T-cell.

00:03:41.958 --> 00:03:43.583
This is a depiction

00:03:43.583 --> 00:03:44.745
this is a, if you want to see

00:03:44.745 --> 00:03:45.666
the whole thing,

00:03:45.666 --> 00:03:48.220
that is a T-cell right over here.

00:03:48.220 --> 00:03:49.581
This is a T-cell.

00:03:49.581 --> 00:03:50.584
And this creepy picture,

00:03:50.584 --> 00:03:51.753
this all the blue,

00:03:51.753 --> 00:03:53.048
that's the T-cell.

00:03:53.048 --> 00:03:54.396
And what you see in yellow

00:03:54.396 --> 00:03:56.896
that's the HIV virus emerging,

00:03:57.952 --> 00:04:00.465
taking advantage of this T-cell.

00:04:00.465 --> 00:04:02.456
So, that's why it's so creepy,

00:04:02.456 --> 00:04:04.663
it's using that cell's machinery

00:04:04.663 --> 00:04:06.511
to reproduce itself.

00:04:06.511 --> 00:04:08.313
But you immediately see on this picture

00:04:08.313 --> 00:04:10.713
how small the HIV virus is

00:04:10.713 --> 00:04:13.657
compared to the actual T-cell.

00:04:13.657 --> 00:04:16.881
Each of these small little things

00:04:16.881 --> 00:04:18.700
each of these small things,

00:04:18.700 --> 00:04:21.162
is an HIV virus, which we already saw

00:04:21.162 --> 00:04:23.612
is a lot bigger than something like

00:04:23.612 --> 00:04:25.604
a hemoglobin protein.

00:04:25.604 --> 00:04:26.800
And so a hemoglobin protein

00:04:26.800 --> 00:04:27.779
you wouldn't even be able to

00:04:27.779 --> 00:04:29.546
on this scale, maybe

00:04:29.546 --> 00:04:30.547
it would be a pixel,

00:04:30.547 --> 00:04:31.380
if that.

00:04:32.585 --> 00:04:34.846
And on a similar scale, is this T-cell,

00:04:34.846 --> 00:04:37.623
you have a, you have things
like red blood cells.

00:04:37.623 --> 00:04:39.450
This is actually a comparison

00:04:39.450 --> 00:04:40.283
this side by side.

00:04:40.283 --> 00:04:41.687
This is using an electron,

00:04:41.687 --> 00:04:43.322
this is using an electron microscope

00:04:43.322 --> 00:04:45.064
you see a red blood cell right over here

00:04:45.064 --> 00:04:45.897
and you see a T-cell

00:04:45.897 --> 00:04:47.243
and they're roughly roughly

00:04:47.243 --> 00:04:48.660
on the same size,

00:04:49.701 --> 00:04:52.003
or at least the same
order of magnitude size.

00:04:52.003 --> 00:04:53.482
And a red blood cell is going to be

00:04:53.482 --> 00:04:55.565
six to eight micrometers,

00:04:56.535 --> 00:04:58.017
micrometers wide.

00:04:58.017 --> 00:04:59.835
So this is six to eight millionths

00:04:59.835 --> 00:05:00.668
of a meter.

00:05:00.668 --> 00:05:01.526
So if we were to

00:05:01.526 --> 00:05:03.126
if we were to just take seven

00:05:03.126 --> 00:05:04.199
as the average.

00:05:04.199 --> 00:05:06.019
Seven millionths,

00:05:06.019 --> 00:05:06.852
seven

00:05:07.847 --> 00:05:09.802
seven millionths

00:05:09.802 --> 00:05:10.853
of a meter.

00:05:10.853 --> 00:05:11.686
Over here, we're talking about

00:05:11.686 --> 00:05:14.061
a millionth of a millimeter.

00:05:14.061 --> 00:05:16.236
Now we're talking about seven millionths

00:05:16.236 --> 00:05:17.917
of a meter.

00:05:17.917 --> 00:05:19.758
And just to get an appreciation for size,

00:05:19.758 --> 00:05:21.495
we already compared the virus,

00:05:21.495 --> 00:05:23.369
the HIV virus, to this cell.

00:05:23.369 --> 00:05:24.525
We're seeing it directly

00:05:24.525 --> 00:05:26.692
as a emerge from the cell.

00:05:27.872 --> 00:05:30.240
But each of these red blood cells

00:05:30.240 --> 00:05:32.159
are gonna contain roughly

00:05:32.159 --> 00:05:34.909
280 million hemoglobin molecules.

00:05:36.688 --> 00:05:39.364
So there's gonna be 200

00:05:39.364 --> 00:05:40.477
each of these there's gonna be

00:05:40.477 --> 00:05:42.806
280 million of these.

00:05:42.806 --> 00:05:44.056
So 280 million,

00:05:45.876 --> 00:05:47.861
that's a million

00:05:47.861 --> 00:05:49.470
million hemoglobins

00:05:49.470 --> 00:05:50.920
in each one of these.

00:05:50.920 --> 00:05:52.195
So hopefully this starts to give you

00:05:52.195 --> 00:05:53.710
an appreciation for

00:05:53.710 --> 00:05:55.588
even though we categorize cells

00:05:55.588 --> 00:05:57.652
as these unimaginably small things,

00:05:57.652 --> 00:05:59.404
they're actually far larger

00:05:59.404 --> 00:06:03.000
they're ginormous compared to things

00:06:03.000 --> 00:06:06.533
even like even like large even proteins.

00:06:06.533 --> 00:06:07.902
And especially when you think of things

00:06:07.902 --> 00:06:09.901
on the molecular, or the atomic scale.

00:06:09.901 --> 00:06:11.284
And that's why cells are so interesting.

00:06:11.284 --> 00:06:13.210
They actually have a lot of

00:06:13.210 --> 00:06:14.771
complexity to them.

00:06:14.771 --> 00:06:16.770
But just to have an appreciation also

00:06:16.770 --> 00:06:19.053
for how small cells are

00:06:19.053 --> 00:06:20.434
even though we've just described

00:06:20.434 --> 00:06:22.253
these red blood cells and these T-cells

00:06:22.253 --> 00:06:25.753
there's these kind of
worlds unto themselves.

00:06:25.753 --> 00:06:28.083
They are these incredibly complex things.

00:06:28.083 --> 00:06:30.549
If I were to draw the width

00:06:30.549 --> 00:06:31.855
of a human hair

00:06:31.855 --> 00:06:33.350
on this screen right now

00:06:33.350 --> 00:06:34.269
relative to the scale

00:06:34.269 --> 00:06:35.515
of these red blood cells,

00:06:35.515 --> 00:06:37.774
it would be about as wide as this video.

00:06:37.774 --> 00:06:39.787
So from if I were to draw a human hair

00:06:39.787 --> 00:06:41.416
it would go from there roughly to there

00:06:41.416 --> 00:06:42.605
and there's actually a lot of variance

00:06:42.605 --> 00:06:44.286
in the width of a human hair.

00:06:44.286 --> 00:06:45.739
But the width of a human hair would be

00:06:45.739 --> 00:06:47.229
just about like that.

00:06:47.229 --> 00:06:48.956
If you looked at the scale of

00:06:48.956 --> 00:06:50.473
if you looked at the scale of

00:06:50.473 --> 00:06:51.586
this picture right over here.

00:06:51.586 --> 00:06:52.652
If you looked at these scales

00:06:52.652 --> 00:06:55.050
it would be much much much bigger.

00:06:55.050 --> 00:06:56.062
And I encourage you

00:06:56.062 --> 00:06:56.938
we can think, oh okay,

00:06:56.938 --> 00:06:58.074
the width of a human hair.

00:06:58.074 --> 00:06:58.976
Pluck a hair out.

00:06:58.976 --> 00:06:59.809
Look at it.

00:06:59.809 --> 00:07:00.642
Put it on a piece of paper.

00:07:00.642 --> 00:07:02.727
It's hard to even discern the width.

00:07:02.727 --> 00:07:03.758
But we're saying that that width

00:07:03.758 --> 00:07:06.196
compared to these red blood cells

00:07:06.196 --> 00:07:07.576
would actually be your entire

00:07:07.576 --> 00:07:08.502
width of the screen.

00:07:08.502 --> 00:07:09.752
We've already said these red blood cells

00:07:09.752 --> 00:07:11.044
these T-cells, these are kind of

00:07:11.044 --> 00:07:13.720
these are worlds unto
themselves when you think of it

00:07:13.720 --> 00:07:17.803
from a viral, or especially
at a molecular scale.


Tertiary structure of proteins

WEBVTT
Kind: captions
Language: en

00:00:00.230 --> 00:00:02.161
- [Voiceover] In the vidoe on protein structure,

00:00:02.161 --> 00:00:04.620
we talked about the different orders of structure,

00:00:04.620 --> 00:00:06.260
starting with primary structure,

00:00:06.260 --> 00:00:08.020
and this is all a bit of a review right now.

00:00:08.020 --> 00:00:11.430
Primary structure is just a sequence of the amino acids.

00:00:11.430 --> 00:00:13.686
But then from there we can start thinking about how does it

00:00:13.686 --> 00:00:17.990
get shaped by thinking about the secondary structure.

00:00:17.990 --> 00:00:22.890
And secondary structure is all about interactions of the

00:00:22.890 --> 00:00:25.870
actual backbone, and we went into some depth

00:00:25.870 --> 00:00:27.746
in the overview video where we talked about

00:00:27.746 --> 00:00:30.720
some of the more typical secondary structures.

00:00:30.720 --> 00:00:33.260
We talked about the parallel beta-pleated sheets,

00:00:33.260 --> 00:00:35.400
and over here I have two backbones.

00:00:35.400 --> 00:00:37.100
They're oriented in the same direction.

00:00:37.100 --> 00:00:39.630
Nitrogen, alpha carbon, carbonyl carbon.

00:00:39.630 --> 00:00:43.260
And I just drew the side chains as these generic R groups.

00:00:43.260 --> 00:00:45.260
And what we saw is you can have hydrogen bonding

00:00:45.260 --> 00:00:48.300
between these backbones, and that was

00:00:48.300 --> 00:00:49.890
a parallel beta-pleated sheet.

00:00:49.890 --> 00:00:51.630
Or if they're oriented the other way,

00:00:51.630 --> 00:00:54.320
this one's going nitrogen, alpha carbon, carbonyl carbon.

00:00:54.320 --> 00:00:57.168
This one's going carbonyl carbon, alpha carbon, nitrogen.

00:00:57.168 --> 00:01:00.360
Well now you have an anti-parallel beta-pleated sheet

00:01:00.360 --> 00:01:03.390
and once again, this is interaction of the backbone.

00:01:03.390 --> 00:01:05.590
Or you could have an alpha helix like this

00:01:05.590 --> 00:01:07.190
where you have hydrogen bonds between

00:01:07.190 --> 00:01:10.800
the different layers of your actual helix.

00:01:10.800 --> 00:01:13.390
And then we can get to tertiary structure,

00:01:13.390 --> 00:01:15.400
and tertiary structure is where we

00:01:15.400 --> 00:01:19.630
finally talk about interactions of the side chains,

00:01:19.630 --> 00:01:21.090
where we start to think about, well,

00:01:21.090 --> 00:01:23.640
what are these R groups and how would these R groups

00:01:23.640 --> 00:01:27.030
actually affect the entire shape of the protein?

00:01:27.030 --> 00:01:29.140
And to help us think about that a little bit,

00:01:29.140 --> 00:01:32.471
I've drawn a few visuals down here.

00:01:32.471 --> 00:01:34.260
And so what you could imagine,

00:01:34.260 --> 00:01:37.700
you could imagine this orangish-brown

00:01:37.700 --> 00:01:40.060
string curve that I've drawn here,

00:01:40.060 --> 00:01:42.050
let's just assume for the sake of visualizing

00:01:42.050 --> 00:01:46.560
that that's our polypeptide backbone.

00:01:46.560 --> 00:01:48.120
And just as a bit of review,

00:01:48.120 --> 00:01:50.290
you could think about your first order,

00:01:50.290 --> 00:01:53.550
your primary structure, which would be about,

00:01:53.550 --> 00:01:58.200
okay, I have that amino acid, then I have this amino acid

00:01:58.200 --> 00:02:00.730
and then I have that amino acid.

00:02:00.730 --> 00:02:04.510
So that sequence, the sequence is your primary structure.

00:02:04.510 --> 00:02:08.040
Then you could have interactions between the backbone,

00:02:08.040 --> 00:02:11.560
and so that could be maybe this is a, this right over here,

00:02:11.560 --> 00:02:14.220
this is an anti-parallel beta-pleated sheet

00:02:14.220 --> 00:02:16.390
right over here where you have hydrogen bonds.

00:02:16.390 --> 00:02:18.900
I'm trying to draw a dotted line, but it's really small.

00:02:18.900 --> 00:02:20.478
Where you have the hydrogen bonds

00:02:20.478 --> 00:02:23.130
right over here between these two backbones.

00:02:23.130 --> 00:02:25.384
I haven't drawn the side chains here.

00:02:25.384 --> 00:02:26.960
You could have an alpha helix here.

00:02:26.960 --> 00:02:28.510
Once again, you have hydrogen bonds

00:02:28.510 --> 00:02:32.350
between the layers of the helix.

00:02:32.350 --> 00:02:34.460
But now let's talk about tertiary structure.

00:02:34.460 --> 00:02:37.130
And tertiary structure's about the side chains.

00:02:37.130 --> 00:02:38.890
So one example of tertiary structure,

00:02:38.890 --> 00:02:41.130
here I've drawn a bunch of side chains.

00:02:41.130 --> 00:02:44.260
This is from valine, I haven't drawn the backbone.

00:02:44.260 --> 00:02:46.590
The backbone's up here.

00:02:46.590 --> 00:02:49.830
And obviously, none of this is drawn quite to scale.

00:02:49.830 --> 00:02:53.190
But the valine side chain, its R group is

00:02:53.190 --> 00:02:56.250
pure hydrocarbon, which is hydrophobic.

00:02:56.250 --> 00:02:58.620
And so one common interaction you might see

00:02:58.620 --> 00:03:00.850
from side chains is hydrophobic side chains

00:03:00.850 --> 00:03:02.960
are not gonna want to be on the outside

00:03:02.960 --> 00:03:06.160
of a protein molecule that's inside of an aqueous solution,

00:03:06.160 --> 00:03:08.330
that's being exposed to water.

00:03:08.330 --> 00:03:11.192
So this might wanna clump into the center,

00:03:11.192 --> 00:03:12.890
and so that might affect how that chain,

00:03:12.890 --> 00:03:17.100
how the polypeptide chain is bent

00:03:17.100 --> 00:03:20.080
or how the whole protein is shaped.

00:03:20.080 --> 00:03:23.270
So these, for example, these might be hydrophobic.

00:03:25.410 --> 00:03:26.590
These would be hydrophobic here

00:03:26.590 --> 00:03:28.760
and kind of they're clumping away from the water.

00:03:28.760 --> 00:03:30.100
And I'm drawing everything in two dimensions,

00:03:30.100 --> 00:03:32.630
but obviously proteins exist in three dimensions,

00:03:32.630 --> 00:03:34.290
which makes their shape so interesting

00:03:34.290 --> 00:03:37.210
and oftentimes hard to fully process.

00:03:37.210 --> 00:03:38.964
You could have something like serine

00:03:38.964 --> 00:03:42.100
which has a hydroxyl group on its side chain.

00:03:42.100 --> 00:03:44.630
And a hydroxyl group, one, since it's polar,

00:03:44.630 --> 00:03:48.798
we know oxygen is a lot more electronegative than hydrogen,

00:03:48.798 --> 00:03:52.197
so the oxygen's going to have a partially negative charge.

00:03:52.197 --> 00:03:54.590
This hydrogen's going to have a partially positive charge.

00:03:54.590 --> 00:03:56.528
So that's going to allow this side chain

00:03:56.528 --> 00:03:59.320
to be more hydrophilic, so it might sit on the outside

00:03:59.320 --> 00:04:02.190
of a protein in contact with an aqueous solution.

00:04:02.190 --> 00:04:04.820
Or it might even allow it to form hydrogen bonds

00:04:04.820 --> 00:04:06.520
with other side chains.

00:04:06.520 --> 00:04:11.130
So let's say that you had the side chains go like this.

00:04:11.130 --> 00:04:14.041
And once again, I'm not drawing it anywhere near to scale.

00:04:14.041 --> 00:04:18.110
I'm exaggerating the size of these side chains.

00:04:18.110 --> 00:04:22.020
But maybe you have another side chain that,

00:04:22.020 --> 00:04:24.060
I'll just draw it like this.

00:04:24.060 --> 00:04:25.760
You have another side chain that at some point,

00:04:25.760 --> 00:04:27.490
you know, it's got a bunch of stuff.

00:04:27.490 --> 00:04:32.000
And then it has a, I'll just draw dots here.

00:04:32.000 --> 00:04:37.120
It has a bunch of stuff, but then it has

00:04:37.120 --> 00:04:42.000
an oxygen bound to a hydrogen.

00:04:42.000 --> 00:04:43.590
Bond to a hydrogen.

00:04:43.590 --> 00:04:45.350
Well, maybe you have some hydrogen bonding

00:04:45.350 --> 00:04:47.250
going on like that, so that would also

00:04:47.250 --> 00:04:49.630
keep this structure in place.

00:04:49.630 --> 00:04:52.405
You could have situations where you have

00:04:52.405 --> 00:04:55.700
ionic side chains, side chains that have charge.

00:04:55.700 --> 00:04:57.850
So maybe this side chain right over here,

00:04:57.850 --> 00:04:59.950
maybe it has a positive charge.

00:04:59.950 --> 00:05:04.528
And our polypeptide backbone,

00:05:04.528 --> 00:05:08.030
let me loop it back this way just like that.

00:05:08.030 --> 00:05:10.134
You could have another side chain.

00:05:10.134 --> 00:05:12.371
You could have another side chain that has

00:05:12.371 --> 00:05:15.420
a net negative charge, and so these

00:05:15.420 --> 00:05:17.290
are going to be attracted to each other

00:05:17.290 --> 00:05:22.420
and you're going to have an ionic bond.

00:05:22.420 --> 00:05:26.231
You can even have covalent bonds between side chains.

00:05:26.231 --> 00:05:29.160
This right over here, this is a typical covalent bond

00:05:29.160 --> 00:05:32.750
that might be formed between two cysteine side chains,

00:05:32.750 --> 00:05:34.780
both of which contain sulfur.

00:05:34.780 --> 00:05:36.320
When they're left to their own devices,

00:05:36.320 --> 00:05:37.990
each of these sulfurs, let me just,

00:05:37.990 --> 00:05:39.960
so it's cysteine, this is the nitrogen,

00:05:39.960 --> 00:05:42.390
this is the alpha carbon, this is the carbonyl carbon.

00:05:42.390 --> 00:05:45.360
So I'm trying to draw the section of it that is cysteine.

00:05:45.360 --> 00:05:48.400
So when it's not in one of these disulfide linkages,

00:05:48.400 --> 00:05:50.390
this sulfur right over here would have

00:05:50.390 --> 00:05:52.000
a covalent bond with a hydrogen.

00:05:52.000 --> 00:05:53.460
But under the right circumstances,

00:05:53.460 --> 00:05:56.100
it can form a covalent bond with another sulfur.

00:05:56.100 --> 00:06:00.350
And in this case, it's another cysteine side chain

00:06:00.350 --> 00:06:02.260
right over here, and this thing over here,

00:06:02.260 --> 00:06:07.060
this is a disulfide bond

00:06:07.060 --> 00:06:10.260
or disulfide linkage, sometimes called.

00:06:10.260 --> 00:06:12.800
And so you can imagine if let's say this was

00:06:12.800 --> 00:06:15.490
a cysteine molecule, this part of the backbone,

00:06:15.490 --> 00:06:17.150
this is cysteine, this is cysteine,

00:06:17.150 --> 00:06:19.360
that their two side chains can form

00:06:19.360 --> 00:06:22.100
this disulfide linkage, and so that would kind of

00:06:22.100 --> 00:06:26.270
provide kind of almost a clip to clip those two parts of,

00:06:26.270 --> 00:06:30.593
or that part of this entire polypeptide together.

00:06:30.593 --> 00:06:32.800
So hopefully this gives you an appreciation

00:06:32.800 --> 00:06:35.500
for all of the interactions that might occur

00:06:35.500 --> 00:06:37.740
to give a protein a structure.

00:06:37.740 --> 00:06:39.600
And then last but not least, of course,

00:06:39.600 --> 00:06:42.800
you have the quaternary structure, which is

00:06:42.800 --> 00:06:46.596
how do you fit together multiple polypeptide chains?

00:06:46.596 --> 00:06:48.230
And all of these, this whole series of videos,

00:06:48.230 --> 00:06:50.250
is just to give you an appreciation for,

00:06:50.250 --> 00:06:51.630
even if you know the sequence,

00:06:51.630 --> 00:06:53.890
the different shapes and the different interactions

00:06:53.890 --> 00:06:55.620
that a protein can actually have,

00:06:55.620 --> 00:06:58.260
and that's what gives proteins their complexity,

00:06:58.260 --> 00:06:59.890
their beauty, their ability to provide

00:06:59.890 --> 00:07:02.590
all of these functions to catalyze reactions as enzymes,

00:07:02.590 --> 00:07:06.200
to be signals as hormones, to provide structural integrity,

00:07:06.200 --> 00:07:09.220
to help transport oxygen, as in the case

00:07:09.220 --> 00:07:11.480
of something like hemoglobin.

00:07:11.480 --> 00:07:13.291
And it's a huge area of research.

00:07:13.291 --> 00:07:16.030
Even if you know the sequence, what is the shape

00:07:16.030 --> 00:07:17.660
of that protein, and based on that shape,

00:07:17.660 --> 00:07:20.300
how can we use that to think about

00:07:20.300 --> 00:07:22.190
how to manipulate that protein in different ways

00:07:22.190 --> 00:07:23.660
or who knows?

00:07:23.660 --> 00:07:26.260
So it's a fascinating area of research.