Osmosis

WEBVTT
Kind: captions
Language: en

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- Let's say that I had two compartments of water,

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and they're separated by a semipermeable membrane.

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Now what do I mean by semipermeable membrane?

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That means they allow some things

00:00:11.079 --> 00:00:13.192
to go through and not other things.

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Let's say this semipermeable membrane,

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it does allow water molecules to pass,

00:00:18.254 --> 00:00:20.437
and in a few seconds we'll talk about what it does not allow

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to pass, which makes it semipermeable.

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Let's just think about what would happen if we just had

00:00:24.755 --> 00:00:26.910
water molecules on either side.

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We've already talked about it in the videos on diffusion.

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The water molecule, since we have an equal concentration

00:00:32.041 --> 00:00:35.060
on either side, the probability that one of these

00:00:35.060 --> 00:00:38.844
water molecules goes this way in a certain amount of time

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is equal to the probability that a water molecule

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goes from right to left in the same amount of time,

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and that's because we have equal concentrations.

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And these things are all bouncing around

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in all different ways, they all have, they all are,

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they all have different velocities.

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They have different speeds and in different directions.

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We just sort of think about it probabilistically.

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The probability of going from left to right

00:01:01.019 --> 00:01:03.155
through one of these gaps is going to be equal

00:01:03.155 --> 00:01:04.966
to the probability of going right to left

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in any given period of time.

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But now let's make this interesting.

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Let's treat our water as solvent,

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and let's put some solute in it.

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So let's dissolve some solute.

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So let's throw some solute particles here.

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And I'm gonna make them bigger so you can see they would

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physically have trouble passing through these gaps.

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There's other ways where you could have semipermeable

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membranes that use charge to allow certain things

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to pass through and not others,

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but it's easier to visualize the size.

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Thinking about the membrane as only allowing

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certain things of certain size to pass through.

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So let's throw some solute there,

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and I'll actually throw a little bit of solute here too.

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I'll do one or two particles right over here,

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but I'm going to do many more.

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I'm going to do many more over there on the right hand side.

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So we have a higher concentration

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of solute on the right hand side,

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and this is a semipermeable membrane.

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You can see even from the size where I drew these gaps

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these big particles aren't going to be able

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to go through the membrane.

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They aren't going to be able to diffuse.

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If they were allowed to diffuse,

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then they would just go down their concentration gradient

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and, in any given moment of time, you would have

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a higher chance of one of these big particles moving from

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the right to the left than from the left to the right,

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'cause you just have more on the right hand side.

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But this is a semipermeable,

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this is a semipermeable membrane.

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These things aren't just going

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to be allowed to naturally diffuse.

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Now all of these big particles,

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they all have their own unique velocities.

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So they all have their unique velocities.

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What do we think is going to happen?

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Let's just think about the problem.

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We know that the big particles can't

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diffuse from one side to another,

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but what's going to happen to the water molecules?

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The water molecules on the left hand side,

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they're not going to be stopped.

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If they are bouncing in the right way,

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they can bounce from the left to the right, or they could

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move from the left to the right through one of these gaps.

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But what about the ones on the right side?

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Well, if things are, if they're the just right conditions,

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if they're the just right conditions

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maybe this character could move through this,

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so you're definitely going to have

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water molecules going back and forth,

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but I'd argue that ones on the right hand side,

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there's a lower probability of water molecules

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from the right hand side moving to the left

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as from the left hand side moving to the right.

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And why is that?

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There's all this interference that play

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from these big molecules that aren't able to diffuse.

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These are going to be bouncing around.

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Sometimes they're going to be even,

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sometimes you can imagine them even blocking,

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they're going to be blocking the approach to these openings.

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If this membrane wasn't here, they wouldn't block

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the approach, they would just keep on going,

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but since that membrane is there,

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they might block it, or they might ricochet off,

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and while they ricochet off they might push on

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some water molecules, they might push on some

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water molecules going in this direction right over there.

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So an argument can be made that these water molecules,

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some of them will still make it from right to left,

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but you have a lower probability of going from right to left

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as you have from going to left to right.

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So because of this you would have a net inflow of water

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from this area where you have a low solute concentration.

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Remember the solute is the thing

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that's dissolved in the water.

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In general, we always consider the solvent

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to be whatever there's more of.

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In this case, it's water,

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and water is probably the most typical solvent,

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and the solute is whatever there's less of.

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So the solute is dissolved in the solvent,

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and so we have a net migration of the water molecules

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from this solution that has a low solute concentration

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to one that has a higher solute concentration.

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This phenomenon we call osmosis.

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We call this osmosis.

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There's other arguments for osmosis.

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It's something that we've observed many, many, many times.

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If you put something that's used to fresh water,

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and if it has skin or it has membranes

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that allows water to pass through it, put it salt water.

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The kind of famous things like slugs

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will not do well in the presence of salt

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because the water inside the slug will do exactly

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what is happening in this diagram.

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This mechanism that I just talked about,

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the molecules that cannot pass through the membrane,

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blocking the water molecules from going right to left,

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ricocheting off and maybe causing the ones

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that are on the right side to maybe move

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in this direction when they bounce into them.

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That's one explanation.

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Another possibility is many times the solute

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that's being dissolved in water

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has some charge associated with it.

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When we think of, say, regular table salt

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you have sodium, you have sodium ions.

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Regular table salt is sodium chloride,

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but when you put it in the water you have sodium ions

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and you have chloride ions, and you have chloride ions.

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These are negatives, the chlorides are negative.

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The sodium ions are positive.

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Above and beyond doing some of the mechanical blockage

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that I just talked about, there's also the idea that

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possibly because they are ionic they have charge,

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and water has partial charges,

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they also might stick to more of the water,

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so the waters that stick to them aren't

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going to be available to move through the membrane.

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So what I mean by the water's going to stick to them?

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Well, when we think about a water molecule, it's an oxygen.

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It's an oxygen then you have a partially negative charge,

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and then you have two hydrogens,

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two, let me write it this way, you have two hydrogens.

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Right over here, there's a partially positive charge.

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So there going to be this oxygen end,

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away from the hydrogens, is going to be attracted

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to the sodium molecule, and it's going to be less.

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The sodium molecule can't make it through.

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This guys going to want to stick to the sodium molecule.

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You can kind of imagine all of these water molecules

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sticking to the sodium molecule,

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which would make it less likely that these would pass

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from right to left than the ones

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that are passing from left to right.

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Similarly, if you have a negatively charged ion like this

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then you can orient the water the other way,

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where the partially positive charged hydrogen ends are going

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to be attracted to the chloride ion right over here.

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Since the chloride ion might not be able to get through,

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well, then these molecules that are stuck to it

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are going to be less likely to flow through.

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These molecules are going to be more attracted

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to the chloride or more attracted to the sodium ions

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than they would be to other water molecules

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that only have partial charges.

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These have full charges, so these can't get through.

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Then maybe it's a lower probability that these

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are going to get through as well.

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But the combined effects of all of these,

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and I'd love if any of y'all to point me to a nice

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simulation or maybe we'll create one on the

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Khan Academy computer science program to show this,

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is that you're going to have a higher probability

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of the water molecules over here going from left to right

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than the water molecules over here going right to left,

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from mechanical blockage and or these big molecules

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ricocheting off and pushing them in the wrong direction,

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or because they're just stuck to the big molecules

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because the big molecules are charged.

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And that is osmosis.


Concentration gradients

WEBVTT
Kind: captions
Language: en

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- In the first video where we introduced

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the idea of diffusion and concentration gradients,

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we had a container with only one type of particle in it,

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we had these purple particles.

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And in our starting scenario we had a higher concentration

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of the purple particles on the left-hand side

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than we had on the right-hand side.

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And so if we looked at its concentration gradient,

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so the concentration gradient went from

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high concentration on the left

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to low concentration on the right.

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And we saw what happened.

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Since you have more of these particles here

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and they're all bouncing around

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in different directions randomly,

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you have a higher probability of things moving

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from the left to the right than from the right to the left.

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You will have things move from the right to the left,

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but you're going to have more things, so you'll have

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a higher probability of things, moving from left to right.

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And so if you let some time pass, then they become

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more uniformly spread across a container.

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They have moved down their concentration gradient

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to make things more uniform.

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Now, what's interesting about this diagram

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is I've introduced a second particle,

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these big yellow particles.

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And we see that their concentration gradient

00:01:04.199 --> 00:01:06.370
is going in the other direction.

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So we have a low concentration,

00:01:08.276 --> 00:01:10.016
in fact we have no, on the left-hand,

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we have none of the yellow particles

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on the left-hand side, and we have

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a high concentration on the right-hand side.

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So their concentration gradient goes from right to left.

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And the whole point of this video

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is to show that each particle moves down

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its unique concentration gradient,

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assuming that it's not blocked in some way,

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it's going to move down its unique concentration gradient

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irrespective of what the other particles

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are going to do, for the most part.

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And so we see the yellow particles are going to move

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from high concentration, to low concentration.

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They're going to move,

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they're going to diffuse from right to left.

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And once again, there's no magic here.

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It's not like this molecule is saying,

00:01:48.845 --> 00:01:52.133
oh, I've got seven other of my friends here,

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it's getting too crowded, I see them, I'm claustrophobic,

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let me move over to the left-hand side.

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That's not what's going on.

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They're just all randomly bouncing around

00:02:00.142 --> 00:02:01.854
and when you're in the starting position,

00:02:01.854 --> 00:02:03.986
when you're exactly like this, there's no probability

00:02:03.986 --> 00:02:07.485
because of a yellow particle moving from left to right,

00:02:07.485 --> 00:02:09.357
because there aren't any yellow particles here.

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While there's a probability that some of these particles,

00:02:13.229 --> 00:02:16.269
in a certain amount of time, some of these yellow particles

00:02:16.269 --> 00:02:18.339
could move from right to left.

00:02:18.339 --> 00:02:19.743
And so they'll keep doing that

00:02:19.743 --> 00:02:21.830
until you get to a stable configuration

00:02:21.830 --> 00:02:24.383
where now you have an equal probability

00:02:24.383 --> 00:02:27.042
of things moving from left to right, and right to left.

00:02:27.042 --> 00:02:29.306
And that's going to be true for each of these particles.

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So the real takeaway, you'll hear in a biology

00:02:32.857 --> 00:02:35.444
or a chemistry class, of things moving down

00:02:35.444 --> 00:02:38.047
their concentration gradient, and you might say,

00:02:38.047 --> 00:02:39.986
and their unique concentration gradient.

00:02:39.986 --> 00:02:42.553
As you see, the yellow particles' concentration gradient

00:02:42.553 --> 00:02:44.909
goes in the other direction as the purple particles,

00:02:44.909 --> 00:02:46.848
but there's no magic to this.

00:02:46.848 --> 00:02:48.870
You just have to imagine a bunch of things

00:02:48.870 --> 00:02:51.193
just bouncing around in a bunch of different directions,

00:02:51.193 --> 00:02:53.393
and then what would just naturally happen?

00:02:53.393 --> 00:02:55.380
You would naturally have a higher probability of moving

00:02:55.380 --> 00:02:57.829
from high concentration to low concentration,

00:02:57.829 --> 00:03:01.492
than from low concentration to high concentration.


Diffusion

WEBVTT
Kind: captions
Language: en

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- Let's say that I have this green container and inside

00:00:03.080 --> 00:00:06.490
this green container I have some air molecules.

00:00:06.490 --> 00:00:07.820
Now the air molecules, we assume that there's

00:00:07.820 --> 00:00:09.340
some temperature, there's some average

00:00:09.340 --> 00:00:11.350
kinetic energy to them but they're all going to have

00:00:11.350 --> 00:00:12.850
different velocities, they're all going to be

00:00:12.850 --> 00:00:14.982
bumping around in different ways.

00:00:14.982 --> 00:00:17.590
Now the way that I've drawn it you might notice something.

00:00:17.590 --> 00:00:19.720
On the left hand side, and I'll just draw

00:00:19.720 --> 00:00:22.350
an imaginary line here, this line has no,

00:00:22.350 --> 00:00:24.690
no real, I guess you could say structural significance,

00:00:24.690 --> 00:00:27.230
it's not like it's actually dividing it, I'm just using it

00:00:27.230 --> 00:00:29.690
to visualize the left and right hand sides.

00:00:29.690 --> 00:00:31.210
You see on the left hand side I have

00:00:31.210 --> 00:00:34.520
a higher concentration of my molecules,

00:00:34.520 --> 00:00:37.620
higher concentration,

00:00:37.620 --> 00:00:38.890
and how do you measure concentration?

00:00:38.890 --> 00:00:41.451
Well the number of molecules per, well the

00:00:41.451 --> 00:00:42.950
real way that you should do it is unit volume

00:00:42.950 --> 00:00:44.350
but we're looking at a cross section here.

00:00:44.350 --> 00:00:46.890
If I were to take a section that large,

00:00:46.890 --> 00:00:48.550
look, I got four molecules here, looks like

00:00:48.550 --> 00:00:51.450
I have about four, three to five molecules

00:00:51.450 --> 00:00:53.420
per section around that size, well if I took

00:00:53.420 --> 00:00:56.090
a that size section on this side I'm getting

00:00:56.090 --> 00:00:57.820
one or maybe two molecules.

00:00:57.820 --> 00:00:58.850
And I'm not going to get too precise

00:00:58.850 --> 00:01:01.450
but it's clear that I have a higher concentration here,

00:01:01.450 --> 00:01:04.250
I have more molecules that we have drawn at per unit area

00:01:04.250 --> 00:01:06.790
but if we're thinking in three dimensions, per unit volume,

00:01:06.790 --> 00:01:09.480
than we have on the right hand side.

00:01:09.480 --> 00:01:11.650
So we have a higher concentration on the left,

00:01:11.650 --> 00:01:14.850
we have a lower concentration on the right,

00:01:14.850 --> 00:01:19.060
lower concentration on the right.

00:01:19.060 --> 00:01:21.250
And when you have this situation where you have

00:01:21.250 --> 00:01:24.320
a higher concentration and then a lower concentration,

00:01:24.320 --> 00:01:27.420
we call this a concentration gradient.

00:01:27.420 --> 00:01:30.250
The concentration is changing from high to low

00:01:30.250 --> 00:01:33.990
and so we call this a concentration,

00:01:33.990 --> 00:01:37.980
concentration...

00:01:37.980 --> 00:01:40.020
concentration gradient.

00:01:40.020 --> 00:01:42.120
Now what do we think is going to happen?

00:01:42.120 --> 00:01:43.950
Let's say this is, this is what our situation is

00:01:43.950 --> 00:01:45.290
right when we look at it,

00:01:45.290 --> 00:01:47.290
what do we think is going to happen?

00:01:47.290 --> 00:01:48.890
Well these, all of these particles are all

00:01:48.890 --> 00:01:51.190
going to be bouncing around, things get moved

00:01:51.190 --> 00:01:53.150
from the left to the right, things get moved

00:01:53.150 --> 00:01:55.650
from the right to the left, but we have

00:01:55.650 --> 00:01:58.020
more particles on the left that are likely

00:01:58.020 --> 00:02:00.690
to move to the right than we have particles on the right

00:02:00.690 --> 00:02:02.610
that are likely to move to the left.

00:02:02.610 --> 00:02:04.250
Remember, they're all moving in different directions

00:02:04.250 --> 00:02:06.850
with these random velocities but I have more

00:02:06.850 --> 00:02:08.990
on this side and they're all bouncing around

00:02:08.990 --> 00:02:10.720
so in any given moment when we have this

00:02:10.720 --> 00:02:12.650
higher concentration on the left I have a

00:02:12.650 --> 00:02:14.510
higher chance that I'm going to have stuff

00:02:14.510 --> 00:02:16.620
go from the left to the right,

00:02:16.620 --> 00:02:18.090
go from the left to the right,

00:02:18.090 --> 00:02:21.120
than I do from the right to the left,

00:02:21.120 --> 00:02:23.620
and so as time goes on,

00:02:23.620 --> 00:02:26.520
as time goes on it's going to look something like this.

00:02:26.520 --> 00:02:29.190
If we let this system stabilize,

00:02:29.190 --> 00:02:31.990
if we let this system stabilize

00:02:31.990 --> 00:02:35.850
for awhile it should look like this.

00:02:35.850 --> 00:02:38.120
Now let me see if I can do a good job,

00:02:38.120 --> 00:02:39.320
a good job drawing it, and I'll just

00:02:39.320 --> 00:02:41.890
draw the molecules, I won't draw their actual,

00:02:41.890 --> 00:02:44.750
their actual velocity vectors.

00:02:44.750 --> 00:02:46.720
So if we wait awhile, how many molecules did I have,

00:02:46.720 --> 00:02:49.560
one, two, three, four, five, six,

00:02:49.560 --> 00:02:52.090
seven, eight, nine, 10, 11, 12, 13, 14,

00:02:52.090 --> 00:02:54.250
15, 16, 17, 18, 19, 20,

00:02:54.250 --> 00:02:57.931
so now I have one, two, three, four five, six, seven, eight,

00:02:57.931 --> 00:03:02.090
nine, 10, 11, 12, 13, 14,

00:03:02.090 --> 00:03:06.590
15, 16, 17, 18, 19, 20.

00:03:06.590 --> 00:03:09.220
So if we let enough time go by we see that

00:03:09.220 --> 00:03:11.390
we don't, we should no longer have

00:03:11.390 --> 00:03:14.190
a concentration gradient, that the concentration

00:03:14.190 --> 00:03:17.382
should be fairly uniform over time.

00:03:17.382 --> 00:03:19.050
So even if I were to draw that imaginary

00:03:19.050 --> 00:03:23.190
dashed line, if I were to draw that imaginary dashed line,

00:03:23.190 --> 00:03:26.390
I should have the same concentration on both sides

00:03:26.390 --> 00:03:28.560
so I no longer have a gradient,

00:03:28.560 --> 00:03:30.950
I have no gradient,

00:03:30.950 --> 00:03:32.810
and once again there's nothing magical here,

00:03:32.810 --> 00:03:35.220
it's not like the molecule said, "Oh, we are less

00:03:35.220 --> 00:03:37.020
"concentrated over there, I somehow have to know

00:03:37.020 --> 00:03:38.850
"to move there," you just have to think

00:03:38.850 --> 00:03:40.810
that these are all just randomly bouncing around

00:03:40.810 --> 00:03:42.720
and if you have a higher concentration on the left

00:03:42.720 --> 00:03:44.790
there's a higher chance that you have bounces

00:03:44.790 --> 00:03:46.890
or you have things moving from the left to the right

00:03:46.890 --> 00:03:48.720
as you do from the right to left.

00:03:48.720 --> 00:03:50.550
Even in this situation things are still going to be

00:03:50.550 --> 00:03:52.950
moving from left to right and right to left,

00:03:52.950 --> 00:03:55.420
but now that you have the same number on either side

00:03:55.420 --> 00:03:58.650
at any given moment, in any given period of time,

00:03:58.650 --> 00:04:00.350
you have an equal probability of things moving

00:04:00.350 --> 00:04:01.920
from the left to the right as you do from

00:04:01.920 --> 00:04:03.690
the right to the left, so you're getting to

00:04:03.690 --> 00:04:05.681
kind of this equilibrium situation.

00:04:05.681 --> 00:04:07.850
Sure, in a given, you know, if you take

00:04:07.850 --> 00:04:10.610
a certain unit of time, maybe that one moves

00:04:10.610 --> 00:04:11.920
from the left to the right, that one moves

00:04:11.920 --> 00:04:13.590
from the left to the right,

00:04:13.590 --> 00:04:15.290
that one moves from the left to the right,

00:04:15.290 --> 00:04:18.350
but since you have equal concentrations on both sides

00:04:18.350 --> 00:04:20.850
you're just as likely to have the same number

00:04:20.850 --> 00:04:22.420
move from right to left.

00:04:22.420 --> 00:04:24.320
And I only did this with 20,

00:04:24.320 --> 00:04:26.090
I only did this with 20 particles,

00:04:26.090 --> 00:04:28.310
which is a little bit of an artificially low number.

00:04:28.320 --> 00:04:30.590
If we're actually talking about concentrations

00:04:30.590 --> 00:04:32.950
of air molecules or as we'll see

00:04:32.950 --> 00:04:34.620
when we think about cellular membranes,

00:04:34.620 --> 00:04:36.850
if we think about different types of molecules

00:04:36.850 --> 00:04:38.190
that might be in an aqueous solution,

00:04:38.190 --> 00:04:40.650
we're talking about way more than 20 molecules

00:04:40.650 --> 00:04:41.820
and so you really do think in terms of

00:04:41.820 --> 00:04:45.090
probabilistic large numbers, well hey, the probability

00:04:45.090 --> 00:04:46.360
of something moving from the left to the right

00:04:46.360 --> 00:04:47.620
is the same as the right to left,

00:04:47.620 --> 00:04:49.190
and so you're going to have this stability.

00:04:49.190 --> 00:04:50.890
Right here there's a much higher probability

00:04:50.890 --> 00:04:52.340
in any given moment of something moving

00:04:52.340 --> 00:04:54.850
from left to right than right to left

00:04:54.850 --> 00:04:57.210
and that's why you see things moving

00:04:57.210 --> 00:04:59.620
from high concentration to low concentration.

00:04:59.620 --> 00:05:01.050
Or another way to think about it,

00:05:01.050 --> 00:05:03.350
what we just observed here is we saw

00:05:03.350 --> 00:05:06.520
things diffusing down their conf--,

00:05:06.520 --> 00:05:08.990
down their concentration gradient.

00:05:08.990 --> 00:05:13.130
So this process that we just described, this is diffusion,

00:05:13.130 --> 00:05:15.750
this is diffusion,

00:05:15.750 --> 00:05:18.420
and as we study different types of systems

00:05:18.420 --> 00:05:20.150
we'll see that this is actually very important

00:05:20.150 --> 00:05:23.190
to biological systems and even chemical systems

00:05:23.190 --> 00:05:26.320
because this doesn't require any extra energy

00:05:26.320 --> 00:05:28.150
to move the molecules from here to there,

00:05:28.150 --> 00:05:29.650
it's going to happen probabilistically,

00:05:29.650 --> 00:05:31.050
it's going to happen naturally and once again,

00:05:31.050 --> 00:05:32.820
no magic, just more stuff here,

00:05:32.820 --> 00:05:34.390
higher chance moving from left to right

00:05:34.390 --> 00:05:36.050
than moving from right to left.

00:05:36.050 --> 00:05:37.580
And I really want to make that point clear.

00:05:37.580 --> 00:05:39.290
You can still move from right to left,

00:05:39.290 --> 00:05:41.920
for example you might have this character,

00:05:41.920 --> 00:05:45.750
maybe his, maybe instead of moving in that direction

00:05:45.750 --> 00:05:48.150
completely possible, completely possible

00:05:48.150 --> 00:05:49.790
that he goes from right to left.

00:05:49.790 --> 00:05:51.920
It's not like everything is moving from left to right

00:05:51.920 --> 00:05:53.120
but you have a higher chance, you're going to have

00:05:53.120 --> 00:05:55.220
more things moving from left to right,

00:05:55.220 --> 00:05:56.910
so that guy could move in that direction

00:05:56.910 --> 00:05:58.250
because there's just more stuff here.

00:05:58.250 --> 00:06:01.490
They're all bouncing around in all, in all different,

00:06:01.490 --> 00:06:04.900
in all different random directions.


Fluid mosaic model of cell membranes

WEBVTT
Kind: captions
Language: en

00:00:00.475 --> 00:00:03.156
- [Voiceover] Let's explore the Fluid Mosaic Model

00:00:03.156 --> 00:00:05.960
of cell membranes.

00:00:05.960 --> 00:00:08.764
Now, why is it called the Fluid Mosaic Model?

00:00:08.764 --> 00:00:11.006
Well, if we were to look at a cell membrane

00:00:11.006 --> 00:00:12.570
and just to be clear what we're looking at,

00:00:12.570 --> 00:00:16.247
if this is a cell right over here,

00:00:16.247 --> 00:00:18.936
and this is its membrane,

00:00:18.936 --> 00:00:21.662
it's kind of what keeps the cell, the inside of the cell,

00:00:21.662 --> 00:00:24.047
separated from whatever is outside the cell.

00:00:24.047 --> 00:00:29.050
We're looking at a cross-section of its surface,

00:00:29.540 --> 00:00:33.170
Where down here, this is inside the cell.

00:00:33.170 --> 00:00:35.236
If we look at it relative to this diagram,

00:00:35.236 --> 00:00:39.496
this is inside the cell, and this is outside.

00:00:39.496 --> 00:00:42.470
And when you zoom in,

00:00:42.470 --> 00:00:44.485
and this little part right over here,

00:00:44.485 --> 00:00:49.337
this is actually a phospholipid bilayer that forms it.

00:00:49.677 --> 00:00:50.964
And so when you hear that you might say,

00:00:50.964 --> 00:00:53.216
well, what is a phospholipid?

00:00:53.216 --> 00:00:54.290
And that's a good question.

00:00:54.290 --> 00:00:56.837
Because when you understand what a phospholipid is,

00:00:56.837 --> 00:00:58.980
it starts to make sense why it would form

00:00:58.980 --> 00:01:01.327
a bilayer like this, and why it's the basis

00:01:01.327 --> 00:01:04.140
for so many membranes in biological systems.

00:01:04.140 --> 00:01:07.271
So this is indicative of a phospholipid

00:01:07.271 --> 00:01:10.144
and as its name implies, and let me write that down,

00:01:10.144 --> 00:01:14.955
this is a phospholipid.

00:01:14.955 --> 00:01:17.852
It's a lipid that involves a phosphate group.

00:01:17.852 --> 00:01:19.116
And in general the word lipid,

00:01:19.116 --> 00:01:20.683
and we have a whole video on lipids,

00:01:20.683 --> 00:01:25.588
means something that doesn't dissolve so well in water.

00:01:25.588 --> 00:01:27.899
And that's true, as the case of this phospholipid,

00:01:27.899 --> 00:01:30.278
you have these hydrocarbon tails

00:01:30.278 --> 00:01:32.218
that are coming from fatty acids,

00:01:32.218 --> 00:01:34.595
and so these hydrocarbon tails,

00:01:34.595 --> 00:01:37.470
they have no obvious charge or no obvious polarity.

00:01:37.470 --> 00:01:39.702
We know that water's a polar molecule

00:01:39.702 --> 00:01:41.547
that's what gives it its hydrogen bonds,

00:01:41.547 --> 00:01:43.537
and it's attracted to itself.

00:01:43.537 --> 00:01:45.649
But these don't have those, and so

00:01:45.649 --> 00:01:47.509
they're not going to be attracted to the water

00:01:47.509 --> 00:01:49.630
and the water's not going to be attracted to it, to them,

00:01:49.630 --> 00:01:52.632
and so these tails are hydrophobic.

00:01:52.632 --> 00:01:57.638
So you have hydrophobic tails,

00:01:58.938 --> 00:01:59.943
and these are really kind of

00:01:59.943 --> 00:02:02.651
the lipid part of the phospholipids.

00:02:02.651 --> 00:02:07.646
And then you have the phosphate head

00:02:08.486 --> 00:02:10.556
right over here,

00:02:10.556 --> 00:02:13.537
and as you can clearly see, this has some charge.

00:02:13.537 --> 00:02:18.388
Charged molecules do well in polar substances like water.

00:02:18.388 --> 00:02:20.604
They're going to dissolve well, and so this part

00:02:20.604 --> 00:02:23.187
right over here, is going to be hydrophilic.

00:02:26.747 --> 00:02:29.921
And actually molecules that have a hydrophilic part

00:02:29.921 --> 00:02:31.274
and a hydrophobic part,

00:02:31.274 --> 00:02:33.317
there's a special word for them.

00:02:33.317 --> 00:02:37.863
Amphipathic, a word that I sometimes have trouble saying.

00:02:37.863 --> 00:02:41.509
So phospholipids are Amphipathic,

00:02:44.109 --> 00:02:47.027
which means that they have both a hydrophilic end,

00:02:47.027 --> 00:02:48.310
a part that is attracted to water,

00:02:48.310 --> 00:02:51.620
and a hydrophobic end, that is not attracted to water.

00:02:51.620 --> 00:02:53.382
And hopefully that starts to explain

00:02:53.382 --> 00:02:56.721
why they organize themselves in this way.

00:02:56.721 --> 00:02:57.969
Because you could image,

00:02:57.969 --> 00:03:00.179
the hydrophilic heads are going to want to be

00:03:00.179 --> 00:03:02.278
where the water is, which is going to be either

00:03:02.278 --> 00:03:04.581
outside the cell or inside the cells.

00:03:04.581 --> 00:03:07.325
And the tails are hydrophobic,

00:03:07.325 --> 00:03:08.484
the water's going to go away from them

00:03:08.484 --> 00:03:09.839
or they're going to go away from the water

00:03:09.839 --> 00:03:11.382
and so they're just going to face each other

00:03:11.382 --> 00:03:14.607
and they're going to be on the inside of the membrane.

00:03:14.607 --> 00:03:16.644
But the really cool thing is, a structure like this,

00:03:16.644 --> 00:03:19.474
having this Amphipathic molecule,

00:03:19.474 --> 00:03:21.969
allows things like these bilipid,

00:03:21.969 --> 00:03:25.925
these lipid bilayers, I should say, to form.

00:03:25.925 --> 00:03:27.195
And it's actually fascinating.

00:03:27.195 --> 00:03:29.942
You would think that if you go far back enough,

00:03:29.942 --> 00:03:33.486
even before life in cellular form, formed,

00:03:33.486 --> 00:03:36.794
that you might have had phospholipids spontaneously forming

00:03:36.794 --> 00:03:41.528
these spheres where you have a bilayer, a lipid bilayer.

00:03:41.528 --> 00:03:43.861
So you could imagine something, let me see,

00:03:43.861 --> 00:03:45.684
if I drew a cross-section,

00:03:45.684 --> 00:03:48.888
let me see if I can draw it relatively neatly.

00:03:48.888 --> 00:03:53.301
So, I think I'll draw half of it, just because you get,

00:03:53.301 --> 00:03:54.948
well I'll draw the whole thing

00:03:54.948 --> 00:03:56.481
and hopefully you get the idea.

00:03:56.481 --> 00:03:59.627
So that would be one layer

00:03:59.627 --> 00:04:02.704
of the phosphate heads facing the outside.

00:04:02.704 --> 00:04:04.896
This is the inner layer,

00:04:04.896 --> 00:04:07.164
and I'm doing a cross-section right over here.

00:04:07.164 --> 00:04:10.293
And then you have your hydrophobic tails,

00:04:11.773 --> 00:04:14.539
let me do that in a different color.

00:04:14.539 --> 00:04:18.527
So your hydrophobic tails, I think you get the picture.

00:04:18.527 --> 00:04:22.152
We have a bunch of hydrophobic tails on either end

00:04:22.152 --> 00:04:24.486
and then you could spontaneously form a structure like this

00:04:24.486 --> 00:04:25.638
which starts to feel like, hey,

00:04:25.638 --> 00:04:27.453
well maybe there's a protocell forming.

00:04:27.453 --> 00:04:30.601
And obviously to actually have real life you have to have

00:04:30.601 --> 00:04:33.274
some form of information that can be passed on,

00:04:33.274 --> 00:04:35.057
and you have to have some type of metabolism,

00:04:35.057 --> 00:04:37.590
and the cell is living, and all of the definitions of life.

00:04:37.590 --> 00:04:39.862
But at least this basic structure of the cellular membrane

00:04:39.862 --> 00:04:44.830
you could imagine how it forms in a pre-life state even,

00:04:45.300 --> 00:04:50.344
by virtue of Amphipathic molecules like a phospholipid.

00:04:50.344 --> 00:04:51.238
So fair enough.

00:04:51.238 --> 00:04:54.354
We're able to form this phospholipid bilayer,

00:04:54.354 --> 00:04:57.187
but what are all these other things that I have drawn here?

00:04:57.187 --> 00:05:02.060
Well, these are proteins and these are examples of,

00:05:02.060 --> 00:05:03.662
this is a protein right over here,

00:05:03.662 --> 00:05:05.954
this is a protein, this is a protein,

00:05:05.954 --> 00:05:08.451
and I just drew some blobs

00:05:08.451 --> 00:05:10.802
to be indicative of the variety of proteins.

00:05:10.802 --> 00:05:12.450
But the important thing to realize is,

00:05:12.450 --> 00:05:15.469
if we think of cells, there's all of this diversity.

00:05:15.469 --> 00:05:18.070
There's all of this complexity that is on,

00:05:18.070 --> 00:05:20.031
or embedded, inside of its membrane.

00:05:20.031 --> 00:05:21.420
So instead of just thinking of it as just kind of

00:05:21.420 --> 00:05:24.938
as a uniform phospholipid bilayer,

00:05:24.938 --> 00:05:28.044
there's all sorts of stuff,

00:05:28.044 --> 00:05:29.678
maybe if we view this as a cross-section,

00:05:29.678 --> 00:05:32.710
there's all sorts of stuff embedded in it

00:05:32.710 --> 00:05:36.012
and we see it right over here in this diagram.

00:05:36.012 --> 00:05:38.582
You could say there's a mosaic of things embedded in it.

00:05:38.582 --> 00:05:41.405
A mosaic is a picture made up of a bunch of

00:05:41.405 --> 00:05:43.179
different components of all different colors,

00:05:43.179 --> 00:05:45.535
and you can see that you have all different components here,

00:05:45.535 --> 00:05:47.497
different types of proteins.

00:05:47.497 --> 00:05:50.747
You have proteins like this, that go across the membrane.

00:05:50.747 --> 00:05:53.057
We call these transmembrane proteins,

00:05:53.057 --> 00:05:55.194
they're a special class of integral protein.

00:05:55.194 --> 00:05:57.051
You have integral proteins like this,

00:05:57.051 --> 00:06:00.974
that might only interact with one part of the bilayer

00:06:00.974 --> 00:06:03.285
while these kind of go across it.

00:06:03.285 --> 00:06:06.159
You have things like glycolipids.

00:06:06.159 --> 00:06:09.674
So this right over here, this is a glycolipid,

00:06:13.543 --> 00:06:14.599
which is fascinating.

00:06:14.599 --> 00:06:16.363
It lodges itself in the membrane

00:06:16.363 --> 00:06:17.838
because it has this lipid end,

00:06:17.838 --> 00:06:19.381
so that's going to be hydrophobic.

00:06:19.381 --> 00:06:20.763
It's going to get along

00:06:20.763 --> 00:06:22.655
with all of the other hydrophobic things,

00:06:22.655 --> 00:06:28.088
but then it has an end that's really a chain of sugars

00:06:28.088 --> 00:06:29.760
and that part is going to be hydrophilic,

00:06:29.760 --> 00:06:31.730
it's going to sit outside of the cell.

00:06:31.730 --> 00:06:33.600
And these chains of sugars,

00:06:33.600 --> 00:06:36.240
these are actually key for cell-cell recognition.

00:06:36.240 --> 00:06:38.687
Your immune system uses these to differentiate

00:06:38.687 --> 00:06:40.127
between which cells are the ones

00:06:40.127 --> 00:06:41.637
that are actually from my body,

00:06:41.637 --> 00:06:43.296
the ones I don't want to mess with,

00:06:43.296 --> 00:06:44.423
the ones I want to protect

00:06:44.423 --> 00:06:46.108
and which cells are the ones that are foreign,

00:06:46.108 --> 00:06:47.954
the ones that I might want to attack.

00:06:47.954 --> 00:06:49.524
When people talk about blood type,

00:06:49.524 --> 00:06:51.355
they're talking about, well, what type of

00:06:51.355 --> 00:06:55.531
specific glycolipids do you have on cells.

00:06:55.531 --> 00:06:58.761
And there's all sorts of, that's not all we're talking about

00:06:58.761 --> 00:07:02.495
when we talk about glycolipids as a way

00:07:02.495 --> 00:07:04.670
for cells to be recognized,

00:07:04.670 --> 00:07:06.868
or to be tagged in different ways.

00:07:06.868 --> 00:07:10.417
So it's a fascinating thing that these chains of sugars

00:07:10.417 --> 00:07:12.762
can lead to such complex behavior, and frankly,

00:07:12.762 --> 00:07:15.492
such useful behavior, from our point of view.

00:07:15.492 --> 00:07:18.741
But you don't just want to have sugar chains on lipids,

00:07:18.741 --> 00:07:21.050
you also have sugar chains on proteins.

00:07:21.050 --> 00:07:24.448
This, right over here, is an example of a glycoprotein.

00:07:27.998 --> 00:07:29.752
And as you can see, when you put all this stuff together,

00:07:29.752 --> 00:07:31.568
you get a mosaic, and I'm actually not even done.

00:07:31.568 --> 00:07:33.473
You have things like cholesterol embedded.

00:07:33.473 --> 00:07:35.483
Cholesterol is a lipid, so it's going to sit in the

00:07:35.483 --> 00:07:37.302
hydrophobic part of the membrane

00:07:37.302 --> 00:07:40.344
and that actually helps with the fluidity of the membrane,

00:07:40.344 --> 00:07:44.786
making sure it's not too fluid or not too stiff.

00:07:44.786 --> 00:07:49.003
So this is cholesterol, right over there.

00:07:49.003 --> 00:07:51.584
So you see this mosaic of stuff,

00:07:51.584 --> 00:07:53.282
but what about the fluid part?

00:07:53.282 --> 00:07:55.541
And I just talked about cholesterol's value

00:07:55.541 --> 00:07:58.269
in making sure that it's just the right amount of fluidity.

00:07:58.269 --> 00:08:01.262
What's neat about this, is this isn't a rigid structure.

00:08:01.262 --> 00:08:04.004
If this thing were to be jostled around a little bit

00:08:04.004 --> 00:08:06.048
or maybe it would be plucked-out somehow,

00:08:06.048 --> 00:08:09.010
the phospholipids would just spontaneously re-arrange

00:08:09.010 --> 00:08:10.307
to fill in the gap.

00:08:10.307 --> 00:08:12.930
You could imagine these things are all flowing around.

00:08:12.930 --> 00:08:16.048
That this membrane actually has a consistency

00:08:16.048 --> 00:08:19.890
of oil or salad dressing.

00:08:19.890 --> 00:08:24.098
So it isn't like a rubbery texture,

00:08:24.098 --> 00:08:26.958
like you might imagine, or a membrane, like a balloon.

00:08:26.958 --> 00:08:30.826
It's actually fluid. These things can move around,

00:08:30.826 --> 00:08:33.167
but even though it's fluid,

00:08:33.167 --> 00:08:35.897
it's good enough to separate the two environments.

00:08:35.897 --> 00:08:37.661
The environment inside the cell

00:08:37.661 --> 00:08:41.792
from the environment outside of the cell.

00:08:41.792 --> 00:08:45.689
And that's where the name Fluid Mosaic Model comes from.


Overview of animal and plant cells

WEBVTT
Kind: captions
Language: en

00:00:00.122 --> 00:00:02.026
- [Voiceover] Let's give ourselves an overview,

00:00:02.026 --> 00:00:04.649
or synthesis, of all that we've learned about plant

00:00:04.649 --> 00:00:07.854
and animal cells, and what I have over here on the left,

00:00:07.854 --> 00:00:12.057
this is supposed to be indicative of an animal cell.

00:00:12.057 --> 00:00:13.786
Animal cell.

00:00:13.786 --> 00:00:16.155
And what I have on the right, this should be indicative

00:00:16.155 --> 00:00:18.117
of a plant cell.

00:00:18.117 --> 00:00:19.708
Plant cell.

00:00:19.708 --> 00:00:21.356
So let's start with the,

00:00:21.356 --> 00:00:22.819
what's outside of the cell.

00:00:22.819 --> 00:00:25.489
So we see in both of them, we see the extracellular matrix.

00:00:25.489 --> 00:00:28.415
You see on this animal or outside of this animal cell,

00:00:28.415 --> 00:00:31.515
you see all these collagen fibers and everything else,

00:00:31.515 --> 00:00:33.883
all these fibers that are holding these cells into place

00:00:33.883 --> 00:00:35.857
and allow these cells to relate to each other,

00:00:35.857 --> 00:00:38.086
and actually, depending on what's inside of it,

00:00:38.086 --> 00:00:40.455
can even help signal different things to the cells,

00:00:40.455 --> 00:00:43.856
so this is an extracellular matrix.

00:00:43.856 --> 00:00:45.818
Now when we think about the extracellular matrix for

00:00:45.818 --> 00:00:47.850
a plant cell, we also think about,

00:00:47.850 --> 00:00:50.184
there's some other components that are involved in the

00:00:50.184 --> 00:00:51.960
actual cell wall,

00:00:51.960 --> 00:00:54.027
and so the cell wall is a key difference between

00:00:54.027 --> 00:00:55.791
plant and animal cells.

00:00:55.791 --> 00:01:00.853
So, the cell wall is going to be in a plant cell.

00:01:00.853 --> 00:01:03.860
Animal cells don't have cell walls.

00:01:03.860 --> 00:01:07.517
Now, if we go one layer deeper, we get to the plasma

00:01:07.517 --> 00:01:09.027
membrane, the cellular membrane,

00:01:09.027 --> 00:01:10.815
and we see that that is common to both.

00:01:10.815 --> 00:01:14.356
The animal cell is going to have a plasma membrane

00:01:14.356 --> 00:01:19.220
and the plant cell is going to have a plasma membrane

00:01:19.220 --> 00:01:21.925
and they actually can both have tunnels

00:01:21.925 --> 00:01:23.911
from neighboring cells,

00:01:23.911 --> 00:01:26.523
or tunnels between neighboring cells.

00:01:26.523 --> 00:01:29.251
We studied that in the cell wall video for plant cells.

00:01:29.251 --> 00:01:33.419
We saw these things right over here, called plasmodesmata,

00:01:33.419 --> 00:01:35.753
And we can actually see a complete one over here,

00:01:35.753 --> 00:01:38.319
because I start to draw a little bit of an adjacent cell.

00:01:38.319 --> 00:01:42.611
Plasmodesmata.

00:01:45.071 --> 00:01:48.524
And in animal cells, the analog are gap junctions,

00:01:48.524 --> 00:01:51.624
which are still tunnels between adjacent cells.

00:01:51.624 --> 00:01:54.758
So, gap junctions.

00:01:54.758 --> 00:01:57.440
Now, plasmodesmata are much more common to a much

00:01:57.440 --> 00:01:59.995
wider category of plant cells than gap junctions

00:01:59.995 --> 00:02:02.758
but gap junctions can be very relevant in certain types

00:02:02.758 --> 00:02:04.395
of animal cells, in particular,

00:02:04.395 --> 00:02:07.286
things like heart cells, where because of gap junctions

00:02:07.286 --> 00:02:08.551
between adjacent cells,

00:02:08.551 --> 00:02:11.488
electrical signals can move through the tissue

00:02:11.488 --> 00:02:14.472
and let adjacent cells know, hey, it's time to contract

00:02:14.472 --> 00:02:16.887
in the right way, so this is still very crucial

00:02:16.887 --> 00:02:19.859
for certain types of animal cells.

00:02:19.859 --> 00:02:22.123
So now let's go a layer even deeper,

00:02:22.123 --> 00:02:24.689
and actually, before I do that, I want to reemphasize this,

00:02:24.689 --> 00:02:26.419
and I do this in almost every video.

00:02:26.419 --> 00:02:28.857
All of these membranes that we draw,

00:02:28.857 --> 00:02:30.587
either the outercellular membrane

00:02:30.587 --> 00:02:32.317
or the membranes of these organelles,

00:02:32.317 --> 00:02:36.218
these are all lipid bilayers, or phospholipid bilayers,

00:02:36.218 --> 00:02:39.178
so if I were to zoom in, right over there,

00:02:39.178 --> 00:02:41.489
on this yellow place right over there,

00:02:41.489 --> 00:02:43.718
it looks just like a line, but it really is,

00:02:43.718 --> 00:02:46.562
it really is a,

00:02:46.562 --> 00:02:49.128
they really are these phospholipid,

00:02:49.128 --> 00:02:51.090
these phospholipid bilayers

00:02:51.090 --> 00:02:54.724
that have these hydrophilic heads that point outwards

00:02:54.724 --> 00:02:58.288
and these hydrophobic tails that point inwards,

00:02:58.288 --> 00:03:00.192
and it keeps going, I want to make that very clear.

00:03:00.192 --> 00:03:02.526
These lipid bilayers, all of these membranes that I draw,

00:03:02.526 --> 00:03:04.755
are lipid bilayers.

00:03:04.755 --> 00:03:06.717
But let's keep on going.

00:03:06.717 --> 00:03:08.656
So as we go now into the cell,

00:03:08.656 --> 00:03:12.139
we see that both of these cells have cytoskeletons.

00:03:12.139 --> 00:03:15.274
We have cytoskeletons, so, you have your

00:03:15.274 --> 00:03:17.294
microfilaments right over here,

00:03:17.294 --> 00:03:19.418
microfilaments right over here,

00:03:19.418 --> 00:03:21.450
and I'm not giving full justice to the complexity,

00:03:21.450 --> 00:03:23.087
just 'cause we want to be able to have a fairly

00:03:23.087 --> 00:03:24.747
simple-looking diagram.

00:03:24.747 --> 00:03:27.023
You have your microtubules,

00:03:27.023 --> 00:03:28.625
microtubules.

00:03:28.625 --> 00:03:31.121
You might have intermediate filaments,

00:03:31.121 --> 00:03:34.256
and we talk about all of those things in other videos,

00:03:34.256 --> 00:03:37.356
but now, let's dig a little bit deeper,

00:03:37.356 --> 00:03:40.827
so in the animal cells, I have these centrosomes, and they

00:03:40.827 --> 00:03:44.426
are key for organizing the microtubules,

00:03:44.426 --> 00:03:47.027
and we're gonna see them a lot when we talk about mitosis.

00:03:47.027 --> 00:03:48.652
We don't see them in plant cells.

00:03:48.652 --> 00:03:51.590
They actually figure out other ways to organize

00:03:51.590 --> 00:03:54.225
their microtubules, especially, well, in general,

00:03:54.225 --> 00:03:56.756
and especially when we're thinking about something like

00:03:56.756 --> 00:04:00.018
mitosis, but let's see what other differences are here.

00:04:00.018 --> 00:04:02.213
Well one big thing that you might notice

00:04:02.213 --> 00:04:07.391
is this big blue, balloon, egg-looking thing,

00:04:07.391 --> 00:04:09.086
and this doesn't contain these green things,

00:04:09.086 --> 00:04:11.350
it's really just behind these green things,

00:04:11.350 --> 00:04:14.159
and this is, these tend to be associated with plant

00:04:14.159 --> 00:04:15.506
and fungal cells.

00:04:15.506 --> 00:04:17.759
This is a central vacuole.

00:04:17.759 --> 00:04:20.951
Central vacuole.

00:04:20.951 --> 00:04:23.552
And a central vacuole can store fluid,

00:04:23.552 --> 00:04:27.360
it can store enzymes, it can be viewed as a place for waste,

00:04:27.360 --> 00:04:30.158
and actually, it turns out that even though they're common

00:04:30.158 --> 00:04:32.817
to plants, that depending on which plants, which cells,

00:04:32.817 --> 00:04:34.117
they can have very different roles,

00:04:34.117 --> 00:04:35.754
and I want to emphasize this to you,

00:04:35.754 --> 00:04:37.495
and I do this in other videos.

00:04:37.495 --> 00:04:39.446
We keep seeing all these organelles,

00:04:39.446 --> 00:04:41.722
and we can draw pictures, we can draw diagrams of them,

00:04:41.722 --> 00:04:44.055
and we think we know what most of their functions are,

00:04:44.055 --> 00:04:47.689
but almost all of these organelles and all of actually,

00:04:47.689 --> 00:04:50.951
the cell, is an area of active research.

00:04:50.951 --> 00:04:53.680
In the decades to come, we're gonna find more

00:04:53.680 --> 00:04:55.154
and more things that these different organelles do,

00:04:55.154 --> 00:04:57.325
and ways that they signal to each other and interact

00:04:57.325 --> 00:04:59.891
with each other and behave in different circumstances,

00:04:59.891 --> 00:05:03.084
so we're starting to understand what's there

00:05:03.084 --> 00:05:04.721
and have an idea of what they do,

00:05:04.721 --> 00:05:06.695
but in the decades to come, we're gonna learn much, much,

00:05:06.695 --> 00:05:09.957
much more about the different structures and functions

00:05:09.957 --> 00:05:11.188
of a cell, but as I mention,

00:05:11.188 --> 00:05:12.720
this is a central vacuole.

00:05:12.720 --> 00:05:15.588
It's large, it can help provide structural support

00:05:15.588 --> 00:05:17.817
for the cell, it can help store things,

00:05:17.817 --> 00:05:19.849
and the best analogue on the animal cells,

00:05:19.849 --> 00:05:22.519
some animal cells actually can have a vacuole,

00:05:22.519 --> 00:05:27.349
not all of them, but the best analogue is the lysosome,

00:05:27.349 --> 00:05:30.089
so this right over, just in the orange color,

00:05:30.089 --> 00:05:32.759
this right over here is a lysosome.

00:05:32.759 --> 00:05:34.559
Lysosome,

00:05:34.559 --> 00:05:35.661
lysosome,

00:05:35.661 --> 00:05:38.761
and a lysosome could be viewed as the waste-disoposal

00:05:38.761 --> 00:05:41.826
of an animal cell, where it's going to have a bunch of

00:05:41.826 --> 00:05:45.820
enzymes in it, so that things can kind of go in there

00:05:45.820 --> 00:05:46.993
and get broken up.

00:05:46.993 --> 00:05:50.220
It has a low, a relatively low pH,

00:05:50.220 --> 00:05:53.657
a more acidic pH so that things can be broken up

00:05:53.657 --> 00:05:57.059
in different ways and then their individual pieces can be

00:05:57.059 --> 00:05:59.857
recycled, and since we're in this category of places where

00:05:59.857 --> 00:06:03.224
things go to get, maybe, broken down or catabolized

00:06:03.224 --> 00:06:04.988
or metabolized in certain ways,

00:06:04.988 --> 00:06:08.605
it's also worth talking about the peroxisomes.

00:06:08.605 --> 00:06:11.533
Peroxisomes.

00:06:13.923 --> 00:06:15.484
So the peroxisomes we actually see in both of them,

00:06:15.484 --> 00:06:17.713
and they're named that way because when they were first

00:06:17.713 --> 00:06:19.361
studied, they said, "hey there's something going on here

00:06:19.361 --> 00:06:22.217
"where there's some oxidation reactions going on here."

00:06:22.217 --> 00:06:25.352
"Well it seems like the final byproduct seems to be hydrogen

00:06:25.352 --> 00:06:28.557
"peroxide," and so that's why they were named peroxisomes

00:06:28.557 --> 00:06:30.658
and we're still understanding exactly all of the things

00:06:30.658 --> 00:06:34.919
that they do, but we know that they're important for

00:06:34.919 --> 00:06:36.927
cutting up long-chain fatty acids,

00:06:36.927 --> 00:06:40.956
so they can be more usable by other parts of the cells,

00:06:40.956 --> 00:06:42.918
but they also have other roles and all of their

00:06:42.918 --> 00:06:47.817
mechanisms are still not fully understood.

00:06:47.817 --> 00:06:50.290
Now going back to differences between the plant cell

00:06:50.290 --> 00:06:53.518
and the animal cells, a key difference is going to be

00:06:53.518 --> 00:06:55.387
these characters right over here.

00:06:55.387 --> 00:06:56.595
These are chloroplasts.

00:06:56.595 --> 00:06:58.220
These are where photosynthesis takes place,

00:06:58.220 --> 00:07:00.554
and clearly we're gonna show it in the plant cell.

00:07:00.554 --> 00:07:02.156
This is how they take, they're able to create,

00:07:02.156 --> 00:07:06.161
they're able to create, essentially, food or,

00:07:06.161 --> 00:07:08.878
I guess you could say, fixed carbon, based on light energy,

00:07:08.878 --> 00:07:11.119
so let me see, chloroplast.

00:07:11.119 --> 00:07:14.219
Chloroplast, right over there.

00:07:14.219 --> 00:07:16.726
We do not see that in the animal cell.

00:07:16.726 --> 00:07:18.294
Now, when we're talking about energy,

00:07:18.294 --> 00:07:20.418
we talk about the ATP factories of cells,

00:07:20.418 --> 00:07:21.983
and we find this in both of these cells,

00:07:21.983 --> 00:07:24.493
and that, of course, are the mitochondria,

00:07:24.493 --> 00:07:27.791
and we see the mitochondria in both of the cells,

00:07:27.791 --> 00:07:29.323
and then the other things we also see a lot of

00:07:29.323 --> 00:07:29.985
common things.

00:07:29.985 --> 00:07:31.726
We see golgi,

00:07:31.726 --> 00:07:34.025
we see the golgi apparatus in that cell,

00:07:34.025 --> 00:07:35.720
we see golgi apparatus in that cell,

00:07:35.720 --> 00:07:39.122
and that's where we package proteins for use

00:07:39.122 --> 00:07:41.653
either within the cell or outside of the cell.

00:07:41.653 --> 00:07:44.114
We have the endoplasmic reticulum.

00:07:44.114 --> 00:07:45.728
We have the rough endoplasmic reticulum

00:07:45.728 --> 00:07:48.155
that has ribosomes bound to the membrane,

00:07:48.155 --> 00:07:50.418
and we have the smooth, where you don't have the ribosomes,

00:07:50.418 --> 00:07:52.857
an this is where a lot of proteins get manufactured,

00:07:52.857 --> 00:07:54.192
but including and all,

00:07:54.192 --> 00:07:56.560
but even lipids also can get manufactured.

00:07:56.560 --> 00:07:58.453
Then you have, of course, the nuclear membrane.

00:07:58.453 --> 00:08:00.357
Actually, this is the inner nuclear membrane

00:08:00.357 --> 00:08:01.251
right over here.

00:08:01.251 --> 00:08:03.259
The outer membrane is contiguous

00:08:03.259 --> 00:08:04.989
with the endoplasmic reticulum,

00:08:04.989 --> 00:08:06.986
but you see that in both of these cells,

00:08:06.986 --> 00:08:08.623
and inside, of course, you have the DNA.

00:08:08.623 --> 00:08:11.583
It's in chromatin form, and then you have this, kind of,

00:08:11.583 --> 00:08:14.416
extra-dense area that shows up in microscopes

00:08:14.416 --> 00:08:17.156
which we call the nucleolus, which is associated,

00:08:17.156 --> 00:08:19.258
which is as associated with ribosomal,

00:08:19.258 --> 00:08:22.555
with ribosome formations and ribosomal RNA,

00:08:22.555 --> 00:08:25.121
and of course, you also have free ribosomes.

00:08:25.121 --> 00:08:28.395
Free, you also have free ribosomes.

00:08:28.395 --> 00:08:32.818
So this is a very high level overview of cells,

00:08:32.818 --> 00:08:34.594
eukaryotic cells, I should say,

00:08:34.594 --> 00:08:36.824
but hopefully it also starts to show you some of the

00:08:36.824 --> 00:08:40.673
key distinctions between animal and plant cells.


Plant cell walls

WEBVTT
Kind: captions
Language: en

00:00:00.190 --> 00:00:02.303
- We've talked a lot about cells in general,

00:00:02.303 --> 00:00:03.766
but what I thought I would do in this video

00:00:03.766 --> 00:00:06.947
is focus on plant cells, and in particular

00:00:06.947 --> 00:00:11.521
focus on the cell walls of plant cells.

00:00:11.521 --> 00:00:13.113
So this right over here, this is a

00:00:13.113 --> 00:00:15.192
drawing of a plant cell.

00:00:15.192 --> 00:00:16.818
And the thing that might jump out

00:00:16.818 --> 00:00:18.176
at you immediately is instead of

00:00:18.176 --> 00:00:21.113
drawing it as just kind of a roundish shape

00:00:21.113 --> 00:00:22.576
like that, the way I've drawn a lot of

00:00:22.576 --> 00:00:24.758
other cells, I've drawn this as kind of

00:00:24.758 --> 00:00:26.732
a cubic structure, or a rectangular prism,

00:00:26.732 --> 00:00:28.364
and that's because plant cells

00:00:28.364 --> 00:00:30.686
can have a structure like that.

00:00:30.686 --> 00:00:31.731
And so the next question is, well,

00:00:31.731 --> 00:00:33.531
what gives them that shape?

00:00:33.531 --> 00:00:35.853
What allows them to form that, kind of,

00:00:35.853 --> 00:00:38.047
cubic rectangular prism shape?

00:00:38.047 --> 00:00:41.587
And the answer is, it's the cell wall.

00:00:41.587 --> 00:00:45.035
So this is the cell wall.

00:00:45.035 --> 00:00:46.428
So let's make sure we can orient

00:00:46.428 --> 00:00:48.472
ourselves properly in this picture.

00:00:48.472 --> 00:00:51.385
So clearly, if I didn't have this cut-out,

00:00:51.385 --> 00:00:52.953
all I would be seeing is the outside.

00:00:52.953 --> 00:00:54.810
All I would be seeing is the cell wall.

00:00:54.810 --> 00:00:56.331
But we've cut it out, and we can see

00:00:56.331 --> 00:00:57.190
the different layers.

00:00:57.190 --> 00:00:58.908
We have the cell wall on the outside.

00:00:58.908 --> 00:01:01.729
Right below that, right below that

00:01:01.729 --> 00:01:03.807
we have the cellular membrane,

00:01:03.807 --> 00:01:05.514
or the plasma membrane.

00:01:05.514 --> 00:01:10.424
So that's the cellular membrane.

00:01:10.424 --> 00:01:14.292
Cellular membrane, right under that.

00:01:14.292 --> 00:01:15.870
And then under that, the cellular membrane

00:01:15.870 --> 00:01:18.656
is containing the cytoplasm.

00:01:18.656 --> 00:01:20.058
And inside of the cytoplasm

00:01:20.058 --> 00:01:21.240
we have all sorts of things.

00:01:21.240 --> 00:01:22.540
This big thing that is taking up

00:01:22.540 --> 00:01:24.550
a lot of the volume inside of this plant cell,

00:01:24.550 --> 00:01:26.186
that's a vacuole, which we have described

00:01:26.186 --> 00:01:30.400
in other videos.

00:01:30.400 --> 00:01:31.166
Vacuole.

00:01:31.166 --> 00:01:32.687
It's the combination of this

00:01:32.687 --> 00:01:34.567
internal pressure, things like the vacuole

00:01:34.567 --> 00:01:35.833
and, just frankly, the pressure

00:01:35.833 --> 00:01:37.934
from all of the fluid inside the cell

00:01:37.934 --> 00:01:40.476
pushing outwards, plus the cell wall

00:01:40.476 --> 00:01:41.811
kind of holding it all in.

00:01:41.811 --> 00:01:43.854
That's what gives plants their structure.

00:01:43.854 --> 00:01:46.408
That's why a plant is able to grow,

00:01:46.408 --> 00:01:48.133
and be upright.

00:01:48.133 --> 00:01:49.763
A plant is able to grow and be upright.

00:01:49.763 --> 00:01:52.154
So that's my drawing of a plant.

00:01:52.154 --> 00:01:53.279
I actually have a plant in my room

00:01:53.279 --> 00:01:54.662
that I'm looking at right now,

00:01:54.662 --> 00:01:56.878
and it's able to grow and be upright.

00:01:56.878 --> 00:01:59.177
And so you have the cell wall,

00:01:59.177 --> 00:02:00.361
you have the cellular membrane,

00:02:00.361 --> 00:02:02.160
you have the other organelles,

00:02:02.160 --> 00:02:03.472
I have some chloroplasts here,

00:02:03.472 --> 00:02:06.340
key for photosynthesis, our good friends

00:02:06.340 --> 00:02:07.037
mitochondria.

00:02:07.037 --> 00:02:08.663
We have our nuclear membrane,

00:02:08.663 --> 00:02:09.614
or I should say this yellow thing

00:02:09.614 --> 00:02:11.076
is the inner nuclear membrane.

00:02:11.076 --> 00:02:12.272
It has the DNA inside.

00:02:12.272 --> 00:02:14.409
Then you have the endoplasmic reticulum,

00:02:14.409 --> 00:02:15.604
kind of containing that.

00:02:15.604 --> 00:02:18.125
The rough ER, containing the ribosomes

00:02:18.125 --> 00:02:19.795
or having the ribosomes on the membrane.

00:02:19.795 --> 00:02:22.379
The smooth ER, not having the ribosomes.

00:02:22.379 --> 00:02:23.517
Golgi apparatus, so that's a little bit

00:02:23.517 --> 00:02:24.260
of a review.

00:02:24.260 --> 00:02:26.744
But our focus here is on the cell wall.

00:02:26.744 --> 00:02:28.021
So let's go back to that.

00:02:28.021 --> 00:02:30.645
So if we zoom in on this, if we zoom in

00:02:30.645 --> 00:02:32.003
on the cell wall right over here, we can

00:02:32.003 --> 00:02:35.412
look at this diagram.

00:02:35.412 --> 00:02:37.165
And over here, it might be a little bit

00:02:37.165 --> 00:02:38.129
surprising to you.

00:02:38.129 --> 00:02:39.893
Because when I've always imagined

00:02:39.893 --> 00:02:43.190
a wall, a cell wall, I imagine something

00:02:43.190 --> 00:02:44.850
like a brick wall.

00:02:44.850 --> 00:02:46.545
Something that's impenetrable.

00:02:46.545 --> 00:02:47.903
But this drawing shows us

00:02:47.903 --> 00:02:48.534
something different.

00:02:48.534 --> 00:02:51.273
And just to be clear what's going on here,

00:02:51.273 --> 00:02:54.524
so this is our cellular membrane --

00:02:54.524 --> 00:02:55.662
sorry I wrote cellular membrane,

00:02:55.662 --> 00:02:57.542
so right over here I have my

00:02:57.542 --> 00:02:59.167
lipid bi-layer.

00:02:59.167 --> 00:03:00.920
And then right on top of that,

00:03:00.920 --> 00:03:02.464
I have the cell wall.

00:03:02.464 --> 00:03:04.020
But you see, it isn't just a thick,

00:03:04.020 --> 00:03:05.564
like a brick wall, like something

00:03:05.564 --> 00:03:06.342
that is impenetrable.

00:03:06.342 --> 00:03:08.722
You see you have all these polysaccharide

00:03:08.722 --> 00:03:10.823
fibers running across it.

00:03:10.823 --> 00:03:12.483
So you have things like cellulose,

00:03:12.483 --> 00:03:15.687
which we saw as a polymer of glucose,

00:03:15.687 --> 00:03:16.767
arranged in a certain way.

00:03:16.767 --> 00:03:19.460
Hemi-cellulose, which has different types

00:03:19.460 --> 00:03:21.747
of monomers associated with it.

00:03:21.747 --> 00:03:22.943
We have pectin, which is another

00:03:22.943 --> 00:03:23.779
polysaccharaide.

00:03:23.779 --> 00:03:25.508
And all of these things -- you've actually

00:03:25.508 --> 00:03:27.726
probably eaten, if not today probably in the

00:03:27.726 --> 00:03:28.979
last week, when we talk about fiber

00:03:28.979 --> 00:03:32.125
in your diet, you're talking about things

00:03:32.125 --> 00:03:33.785
like the cellulose and the pectin.

00:03:33.785 --> 00:03:35.167
Things that your body can't digest.

00:03:35.167 --> 00:03:36.665
When you eat a plant you're getting it,

00:03:36.665 --> 00:03:38.487
because you're eating their cell walls.

00:03:38.487 --> 00:03:40.797
And it does cool things, like

00:03:40.797 --> 00:03:42.283
slows the absorption of glucose in your

00:03:42.283 --> 00:03:43.026
intestines.

00:03:43.026 --> 00:03:44.965
It absorbs water, so I guess you could say

00:03:44.965 --> 00:03:47.844
things pass a little bit easier.

00:03:47.844 --> 00:03:50.479
But the key thing here is this isn't

00:03:50.479 --> 00:03:51.060
a wall.

00:03:51.060 --> 00:03:52.604
This actually allows --

00:03:52.604 --> 00:03:53.161
Or, it is a wall,

00:03:53.161 --> 00:03:53.881
It's officially the cell wall.

00:03:53.881 --> 00:03:56.481
But it's not a thick, impenetrable wall

00:03:56.481 --> 00:03:57.236
like you might associate the wall

00:03:57.236 --> 00:03:59.279
of the room that you're in.

00:03:59.279 --> 00:04:00.684
You can see that it has space

00:04:00.684 --> 00:04:02.657
for small molecules to flow.

00:04:02.657 --> 00:04:04.445
And it's really more like a mesh,

00:04:04.445 --> 00:04:05.559
or like a fabric.

00:04:05.559 --> 00:04:07.254
And so the cellular membrane

00:04:07.254 --> 00:04:10.876
actually has access to the fluid,

00:04:10.876 --> 00:04:12.757
and to the molecules, that are

00:04:12.757 --> 00:04:14.417
between the cells.

00:04:14.417 --> 00:04:15.601
And so just to be clear what we're

00:04:15.601 --> 00:04:16.182
looking at.

00:04:16.182 --> 00:04:18.120
This layer right here, this cellular membrane,

00:04:18.120 --> 00:04:19.618
that's the lipid bi-layer.

00:04:19.618 --> 00:04:22.218
This right over here, this is the

00:04:22.218 --> 00:04:24.459
cell wall.

00:04:24.459 --> 00:04:25.573
I'll do that in a different color.

00:04:25.573 --> 00:04:29.114
That is the cell wall.

00:04:29.114 --> 00:04:30.554
And then right above the cell wall,

00:04:30.554 --> 00:04:32.353
that's the space between the cells,

00:04:32.353 --> 00:04:35.297
which we cell the middle lamella.

00:04:35.297 --> 00:04:36.814
So the space between the cells

00:04:36.814 --> 00:04:39.960
we call the middle lamella.

00:04:39.960 --> 00:04:42.456
So this also is, right over here, is also

00:04:42.456 --> 00:04:45.753
the middle lamella.

00:04:45.753 --> 00:04:47.576
So all of that is interesting, but you might say,

00:04:47.576 --> 00:04:49.073
"Okay, well, how hard is a cell?

00:04:49.073 --> 00:04:51.395
I get that it's a mesh, but clearly the cells,

00:04:51.395 --> 00:04:54.216
the plants are able to stand upright.

00:04:54.216 --> 00:04:55.934
Is that because the cell wall provides

00:04:55.934 --> 00:04:57.316
all of that rigidity?"

00:04:57.316 --> 00:04:59.417
And the answer is, kind of.

00:04:59.417 --> 00:05:00.879
The cell wall is like this mesh.

00:05:00.879 --> 00:05:02.598
It helps the cells have their shape.

00:05:02.598 --> 00:05:04.455
But if you stop watering a plant,

00:05:04.455 --> 00:05:07.938
you're going to see it kind of

00:05:07.938 --> 00:05:08.862
wilt over.

00:05:08.862 --> 00:05:11.339
And that's because part of its ability

00:05:11.339 --> 00:05:13.313
to stand up is from the internal pressure

00:05:13.313 --> 00:05:14.137
of the cells.

00:05:14.137 --> 00:05:16.470
But also part of its shape is the actual

00:05:16.470 --> 00:05:17.875
cell wall.

00:05:17.875 --> 00:05:18.839
Now, some of you might be saying,

00:05:18.839 --> 00:05:20.011
"Well I've seen plants that are much,

00:05:20.011 --> 00:05:21.079
much more rigid than this plant

00:05:21.079 --> 00:05:22.170
that you've just drawn.

00:05:22.170 --> 00:05:23.610
What about things like trees?

00:05:23.610 --> 00:05:24.829
What about wood?

00:05:24.829 --> 00:05:26.345
Wood seems very rigid.

00:05:26.345 --> 00:05:27.750
In fact, so rigid that we can build

00:05:27.750 --> 00:05:30.304
actual walls out of wood."

00:05:30.304 --> 00:05:32.463
And the answer there is these

00:05:32.463 --> 00:05:34.669
more mature plants, actually once the cell

00:05:34.669 --> 00:05:37.142
has stopped growing and you have your

00:05:37.142 --> 00:05:40.021
cell wall, more layers of cellulose and

00:05:40.021 --> 00:05:41.867
other molecules can be built to form

00:05:41.867 --> 00:05:43.945
what's called a secondary cell wall.

00:05:43.945 --> 00:05:45.303
So this could be viewed as a primary

00:05:45.303 --> 00:05:45.860
cell wall.

00:05:45.860 --> 00:05:47.381
And then a thicker, secondary cell wall

00:05:47.381 --> 00:05:48.890
could be built, which gives much,

00:05:48.890 --> 00:05:50.666
much more rigidity.

00:05:50.666 --> 00:05:52.117
And so when you look at wood,

00:05:52.117 --> 00:05:53.151
what gives wood its structure,

00:05:53.151 --> 00:05:54.277
even if you were to take out all of the

00:05:54.277 --> 00:05:55.728
water, even if you were to dehydrate

00:05:55.728 --> 00:05:57.736
the wood, it's still going to have

00:05:57.736 --> 00:05:59.710
its rigidity, because the cellulose layers

00:05:59.710 --> 00:06:00.836
and the other molecules that are

00:06:00.836 --> 00:06:02.252
so thick that it's able to have its

00:06:02.252 --> 00:06:04.446
rigid form.

00:06:04.446 --> 00:06:05.596
Now that last thing I want to talk about.

00:06:05.596 --> 00:06:06.873
We've already seen that the

00:06:06.873 --> 00:06:08.486
cellular membrane has access to

00:06:08.486 --> 00:06:11.655
the molecules floating around between

00:06:11.655 --> 00:06:14.349
cells, but there's actually also

00:06:14.349 --> 00:06:18.493
direct tunnels between adjacent plant cells.

00:06:18.493 --> 00:06:21.105
And those direct tunnels I've drawn here

00:06:21.105 --> 00:06:22.313
on this, outside of the cell walls

00:06:22.313 --> 00:06:24.460
these little yellow circles, these are

00:06:24.460 --> 00:06:26.236
plasmodesmata.

00:06:26.236 --> 00:06:29.371
These are plasmodesmata.

00:06:29.371 --> 00:06:30.613
To get a better understanding of what

00:06:30.613 --> 00:06:32.737
they're like, imagine this is one cell.

00:06:32.737 --> 00:06:35.059
So I'm writing here Cell 1.

00:06:35.059 --> 00:06:37.021
And let's say this is Cell 2.

00:06:37.021 --> 00:06:38.019
Cell 2 right over here.

00:06:38.019 --> 00:06:39.041
And I have a cross-section.

00:06:39.041 --> 00:06:43.116
You see the plasmodesmata are these

00:06:43.116 --> 00:06:46.030
tunnels that form between not just the

00:06:46.030 --> 00:06:48.201
membrane of the cell wall and the

00:06:48.201 --> 00:06:49.536
plasmodesmata.

00:06:49.536 --> 00:06:51.254
It forms between the two cells.

00:06:51.254 --> 00:06:52.391
And so you can actually have a

00:06:52.391 --> 00:06:54.771
flow of cytosol and small molecules

00:06:54.771 --> 00:06:58.892
directly between these two cells.

00:06:58.892 --> 00:07:00.030
And if you want to get a little bit more

00:07:00.030 --> 00:07:01.412
involved in the structure, you have this

00:07:01.412 --> 00:07:04.871
kind of smooth endoplasmic reticulum pipe

00:07:04.871 --> 00:07:05.498
going through it.

00:07:05.498 --> 00:07:06.775
But I want to make it very clear.

00:07:06.775 --> 00:07:08.574
'Cause a lot of times when you

00:07:08.574 --> 00:07:10.234
study biology it's all explained,

00:07:10.234 --> 00:07:11.593
it seems all neat and clean and textbook.

00:07:11.593 --> 00:07:13.369
But people are still studying exactly

00:07:13.369 --> 00:07:15.470
why do we have these things?

00:07:15.470 --> 00:07:17.687
What are they necessary?

00:07:17.687 --> 00:07:19.870
What gets transported across these things,

00:07:19.870 --> 00:07:21.553
and how are they able to transport,

00:07:21.553 --> 00:07:22.853
and under what conditions are they?

00:07:22.853 --> 00:07:24.467
So all of these areas, when you were to

00:07:24.467 --> 00:07:25.907
kind of dig one layer deeper

00:07:25.907 --> 00:07:27.590
than frankly I'm talking about,

00:07:27.590 --> 00:07:29.389
you're getting into an area of

00:07:29.389 --> 00:07:30.655
active research.

00:07:30.655 --> 00:07:32.315
So anyway, hopefully this whole thing

00:07:32.315 --> 00:07:34.091
gives you a little bit more appreciation

00:07:34.091 --> 00:07:35.589
for the wood around you, the

00:07:35.589 --> 00:07:36.773
plants, the house plants around you,

00:07:36.773 --> 00:07:39.547
and even the salad that you might have

00:07:39.547 --> 00:07:41.547
for lunch.


Extracellular matrix

WEBVTT
Kind: captions
Language: en

00:00:00.360 --> 00:00:02.130
- [Voiceover] We've given a lot of importance

00:00:02.130 --> 00:00:04.760
to individual cells and that's for good reason.

00:00:04.760 --> 00:00:07.400
Cells are the basic unit of life

00:00:07.400 --> 00:00:09.120
and they are fascinating in their own right.

00:00:09.120 --> 00:00:10.160
As we've seen in other videos,

00:00:10.160 --> 00:00:12.750
there's whole universes inside of cells.

00:00:12.750 --> 00:00:14.890
There's a lot more complexity than many

00:00:14.890 --> 00:00:17.617
of us might have guessed before really studying cells.

00:00:17.617 --> 00:00:21.260
But how do we go from cells to tissues?

00:00:21.260 --> 00:00:23.550
So when you know if you look even

00:00:23.550 --> 00:00:26.720
if you look at your skin, that tissue of your skin,

00:00:26.720 --> 00:00:31.800
or your tendons or, if you think about heart's tissues

00:00:31.800 --> 00:00:33.190
or the different organs' tissues.

00:00:33.190 --> 00:00:34.290
How do you go from a different tissue,

00:00:34.290 --> 00:00:35.960
which of course, eventually, will then get you

00:00:35.960 --> 00:00:38.960
to a full multi-cellular organism.

00:00:38.960 --> 00:00:41.890
So all the tissues and organs together,

00:00:41.890 --> 00:00:44.350
you're going to get the whole organism.

00:00:44.350 --> 00:00:46.750
How do the cells get together, coordinate,

00:00:46.750 --> 00:00:50.220
structure themselves to form me or you?

00:00:50.220 --> 00:00:53.800
And the answer is, or at least it involves,

00:00:53.800 --> 00:00:56.850
something called the extracellular matrix.

00:00:56.850 --> 00:00:59.880
Extracellular

00:01:01.710 --> 00:01:02.773
matrix.

00:01:02.773 --> 00:01:05.353
And just as we've talked about the insides of a cell,

00:01:05.353 --> 00:01:07.683
not just being a bunch of organelles floating around

00:01:07.683 --> 00:01:10.243
that we have a cytoskeleton that gives the inside

00:01:10.243 --> 00:01:13.123
of the cell structure and allows it to even,

00:01:13.123 --> 00:01:15.093
potentially, move and divide

00:01:15.093 --> 00:01:16.663
and transport things.

00:01:16.663 --> 00:01:19.333
So if you assume that this blob

00:01:19.333 --> 00:01:21.693
right over here is a cell,

00:01:21.693 --> 00:01:22.593
what I just drew in yellow,

00:01:22.593 --> 00:01:25.093
that would be its cytoskeleton on the inside,

00:01:25.093 --> 00:01:27.493
but there's also an analogous thing on the outside

00:01:27.493 --> 00:01:31.383
that helps coordinate how the cells all relate to each other

00:01:31.383 --> 00:01:32.723
and that's what we're talking about

00:01:32.723 --> 00:01:36.603
when we talk about the extracellular matrix.

00:01:37.233 --> 00:01:39.102
And it's made up of a bunch of different types

00:01:39.102 --> 00:01:42.713
of fibers and proteins and glycoproteins

00:01:42.713 --> 00:01:45.593
and probably the most notable of these

00:01:45.593 --> 00:01:47.263
is collagen.

00:01:47.263 --> 00:01:49.263
So I'll do colagen in yellow right over here.

00:01:49.263 --> 00:01:53.653
So these could be strands of collagen right over here

00:01:53.653 --> 00:01:58.033
and collagen is actually the most common protein in mammals.

00:01:58.033 --> 00:02:01.983
It makes up approximately, so this is collagen

00:02:01.983 --> 00:02:03.617
in the yellow right over there,

00:02:03.617 --> 00:02:05.523
and it makes approximately, I've seen estimates

00:02:05.523 --> 00:02:08.793
of 25 to 35%, but I'll just go with it makes

00:02:08.793 --> 00:02:12.993
approximately 30% of the proteins in mammals.

00:02:12.993 --> 00:02:17.213
30% of mammalian, I'll say mammal,

00:02:17.213 --> 00:02:18.923
mammal protein.

00:02:18.923 --> 00:02:23.283
So roughly 30% of the protein in your body is collagen

00:02:23.283 --> 00:02:25.823
and a lot of it is making up these strands

00:02:25.823 --> 00:02:28.353
that help make up, it's not the only protein found,

00:02:28.353 --> 00:02:31.623
that help make up the extracellular matrix.

00:02:31.623 --> 00:02:32.853
And you see these cells here,

00:02:32.853 --> 00:02:34.423
these things that I've drawn,

00:02:34.423 --> 00:02:37.083
they're kind of embedded in this the way I've drawn it.

00:02:37.083 --> 00:02:38.653
They can be fixed.

00:02:38.653 --> 00:02:40.463
They look like they're a little bit, they're attached

00:02:40.463 --> 00:02:42.753
to this matrix and it helps position them.

00:02:42.753 --> 00:02:44.816
And it is true that the extracellular matrix,

00:02:44.816 --> 00:02:48.163
the collagen fibers and other things that we find there

00:02:48.163 --> 00:02:52.033
help attach the cells and structure the cells into tissues.

00:02:52.033 --> 00:02:54.263
They also help inform the cell,

00:02:54.263 --> 00:02:56.293
let the cell know when to grow, when to divide,

00:02:56.293 --> 00:02:58.383
even potentially when to die or when to produce

00:02:58.383 --> 00:03:01.053
different types of molecules.

00:03:01.053 --> 00:03:02.333
And to get a little bit deeper,

00:03:02.333 --> 00:03:03.933
to understand what's actually going on,

00:03:03.933 --> 00:03:05.693
how the cell actually attaches,

00:03:05.693 --> 00:03:06.833
if we were to zoom in,

00:03:06.833 --> 00:03:10.563
let's say we were to zoom in right over there on that square

00:03:10.563 --> 00:03:12.723
so I'm zooming in on the cellular membrane,

00:03:12.723 --> 00:03:14.313
we could get to this bigger picture

00:03:14.313 --> 00:03:18.123
that is taking up most of the screen right over here,

00:03:18.123 --> 00:03:20.963
so a view of this is like zoomed in representation.

00:03:20.963 --> 00:03:23.863
So right over here this is inside the cell.

00:03:23.863 --> 00:03:26.993
This is inside the cell here

00:03:26.993 --> 00:03:28.953
and we an see that we even have

00:03:28.953 --> 00:03:32.783
an actin microfilament right over here

00:03:32.783 --> 00:03:36.523
that helps form, this is part of the cytoskeleton

00:03:36.523 --> 00:03:38.093
and then have the collagen fibers

00:03:38.093 --> 00:03:41.710
which is making up part of the extracellular matrix

00:03:41.710 --> 00:03:44.193
and then we see that it all gets attached

00:03:44.193 --> 00:03:46.333
with these proteins and these proteins,

00:03:46.333 --> 00:03:49.583
they're a class of proteins called integrins.

00:03:49.583 --> 00:03:50.583
Integrins.

00:03:50.583 --> 00:03:53.053
And they're embedded in the membranes

00:03:53.053 --> 00:03:55.884
of cells and through other fibers,

00:03:55.884 --> 00:03:58.023
it's something like a fibronectin,

00:03:58.023 --> 00:04:01.963
they can be attached to the broader

00:04:01.963 --> 00:04:03.921
extracellular matrix

00:04:03.921 --> 00:04:05.361
and this is fascinating because it obviously

00:04:05.361 --> 00:04:09.221
structurally connects this extracellular,

00:04:09.221 --> 00:04:10.761
I guess you could say structure,

00:04:10.761 --> 00:04:13.591
this extracellular matrix to the inside of the cell,

00:04:13.591 --> 00:04:16.776
to the cytoskeleton, through these proteins

00:04:16.776 --> 00:04:18.661
and as I mentioned, these proteins help

00:04:18.661 --> 00:04:21.561
kind of lodge things together, lock them in place,

00:04:21.561 --> 00:04:23.961
but they can also be used to signal,

00:04:23.961 --> 00:04:25.561
they can sense tension depending

00:04:25.561 --> 00:04:26.831
on what type of cells you have,

00:04:26.831 --> 00:04:28.951
they can signal for the cell itself

00:04:28.951 --> 00:04:33.421
to get active or deactivate in some interesting ways.

00:04:33.421 --> 00:04:34.751
So it's a fascinating thing

00:04:34.751 --> 00:04:36.511
and I wanna make it very clear to you,

00:04:36.511 --> 00:04:38.161
a lot of times when you're studying biology

00:04:38.161 --> 00:04:39.761
even an introductory biology class

00:04:39.761 --> 00:04:41.801
you'll see things like this in textbooks,

00:04:41.801 --> 00:04:43.561
it's like, "Oh, of course, we have intogren proteins

00:04:43.561 --> 00:04:46.561
"that are going across our cellular membrane

00:04:46.561 --> 00:04:48.121
"and they're attached to things like fibronectin

00:04:48.121 --> 00:04:50.151
"and they're attached to the cytoskeleton

00:04:50.151 --> 00:04:54.091
"and they get attached to the collagen fibers

00:04:54.091 --> 00:04:55.791
"throughout the extracellular matrix."

00:04:55.791 --> 00:04:57.201
And it seems like oh, all of the biology

00:04:57.201 --> 00:04:58.761
is already figured out,

00:04:58.761 --> 00:05:01.191
but the real answer is how all of these things

00:05:01.191 --> 00:05:03.621
actually work together and how they signal

00:05:03.621 --> 00:05:05.001
to each other and how cells know

00:05:05.001 --> 00:05:06.701
what to do based on how much stress

00:05:06.701 --> 00:05:08.791
or tension or how crowded a certain area is.

00:05:08.791 --> 00:05:11.541
These are areas of open research.

00:05:11.541 --> 00:05:12.951
In fact everything that I'm talking about,

00:05:12.951 --> 00:05:15.091
if you were to delve a little bit deeper,

00:05:15.091 --> 00:05:17.001
and I encourage you to do web searches on these,

00:05:17.001 --> 00:05:19.231
you'll find current research papers

00:05:19.231 --> 00:05:20.521
where people are saying, "Well, how exactly

00:05:20.521 --> 00:05:22.591
"does an intogren know what to do?"

00:05:22.591 --> 00:05:24.670
or "How does it exactly signal to the cell?"

00:05:24.670 --> 00:05:28.891
or "How does it exactly bind itself

00:05:28.891 --> 00:05:32.621
"to either the cytoskeleton or the extracellular matrix?"

00:05:32.621 --> 00:05:34.791
These are all interesting areas of research

00:05:34.791 --> 00:05:36.000
and people are gonna be researching them

00:05:36.000 --> 00:05:37.721
for some time because there's always more questions

00:05:37.721 --> 00:05:40.801
on how these incredibly complex proteins

00:05:40.801 --> 00:05:44.001
and glycoproteins, fibronectin is a glycoprotein,

00:05:44.001 --> 00:05:45.980
it's proteins where the side chains

00:05:45.980 --> 00:05:48.961
have

00:05:48.961 --> 00:05:52.551
carbohydrate chains, saccharide chains,

00:05:52.551 --> 00:05:54.121
branching off of them.

00:05:54.121 --> 00:05:55.861
And so how do all of these thing interact

00:05:55.861 --> 00:05:57.951
and how do they kind of "know what to do"

00:05:57.951 --> 00:06:00.091
and how do all of these complex signaling mechanisms work?

00:06:00.091 --> 00:06:01.751
So it's a fascinating area of research.

00:06:01.751 --> 00:06:03.792
But, hopefully this gives you an appreciation

00:06:03.792 --> 00:06:06.498
for even a further appreciation for the complexity

00:06:06.498 --> 00:06:07.631
that makes you you.

00:06:07.631 --> 00:06:09.867
We've already talked about cells themselves being complex,

00:06:09.867 --> 00:06:12.751
but now they're lodged in this extracellular matrix

00:06:12.751 --> 00:06:14.751
which helps us better define tissues

00:06:14.751 --> 00:06:17.551
and helps kind of let the cells live

00:06:17.551 --> 00:06:18.921
in this community and know how

00:06:18.921 --> 00:06:21.891
to relate to each other and have a little bit of signaling

00:06:21.891 --> 00:06:24.811
from their outside environment.

00:06:24.811 --> 00:06:26.091
And I've just drawn one

00:06:26.091 --> 00:06:29.451
kind of intogren complex right over here,

00:06:29.451 --> 00:06:30.621
but you would have many along the cell

00:06:30.621 --> 00:06:33.046
or along the membrane

00:06:33.046 --> 00:06:34.551
and these aren't the only proteins.

00:06:34.551 --> 00:06:36.051
The fascinating things about cellular membranes,

00:06:36.051 --> 00:06:39.021
you'll often just see them drawn as this lipid bilayer.

00:06:39.021 --> 00:06:40.591
They have all sorts of proteins

00:06:40.591 --> 00:06:42.191
that are lodged inside of them

00:06:42.191 --> 00:06:44.221
that are used as receptors that allow certain molecules

00:06:44.221 --> 00:06:45.791
in and certain molecules out.

00:06:45.791 --> 00:06:48.691
So they really almost cities unto themselves

00:06:48.691 --> 00:06:49.891
and then they interact with

00:06:49.891 --> 00:06:52.251
their broader environment as well.