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Lecture Comments (2)

1 answer

Last reply by: Professor Hovasapian
Fri Jul 6, 2018 5:22 AM

Post by Swati Sharma on July 4 at 01:56:32 PM

I secured 95% in my Biochemistry class last semester and it was all due to your lectures. Now I am using the same lectures to prepare myself for MCAT Biochemistry. I am using only for MCAT prep since it has helped me preventing to spend 5000 dollars on MCAT prep classes(Kaplan, Princeton etc.)  which mainly does content reviews  which I can do it myself via

Can I use your AP chemistry videos for MCAT prep? I am not sure what AP means but I am assuming its university level course. Please let me know and thanks for great lectures.


Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Recap Example: Draw the Structure of Gal(α1↔β1)Man 0:38
  • Polysaccharides 9:46
    • Polysaccharides Overview
    • Homopolysaccharide
    • Heteropolysaccharide
    • Homopolysaccharide as Fuel Storage
    • Starch Has Two Types of Glucose Polymer: Amylose
    • Starch Has Two Types of Glucose Polymer: Amylopectin
    • Polysaccharides: Reducing End & Non-Reducing End
    • Glycogen
    • Examples: Structures of Polysaccharides
    • Let's Draw an (α1→4) & (α1→6) of Amylopectin by Hand.
    • More on Glycogen
    • Glycogen, Concentration, & The Concept of Osmolarity

Transcription: Polysaccharides

Hello and welcome back to and welcome back to Biochemistry.0000

Today's lesson, we're going to start talking about polysaccharides.0004

These are just long chains of individual sugar units, glucose, galactose, mannose any number of possible, so, it is just long chains of them- that is all.0008

Instead of a disaccharide, so now we have multiple monomers.0019

Let’s go ahead and get started.0023

Before we do though, I just want to do a quick recap, one more example for disaccharides just so we can get a little bit more practice with actually drawing the structures out by hand.0025

We need to be able to draw them out by hand, not just by recognize them passively.0033

Let's do a recap example here before we get started.0039

OK, so, a recap example.0047

We would like you to draw the structure of galactose - oops let me make this L a little bit better here - of Gal(alpha1)(beta1)Man.0051

Galactose, alpha-1, beta-1, so the glycosidic bond between the galactose and the mannose is going to be the alpha-1 carbon of the galactose, the beta-1 of configuration of mannose.0074

Let's go ahead and draw this out.0085

Let's see; the first thing we are going to do, I’m going to start off by drawing the linear structures and then the rings, and then I'll put the rings together.0090

It is always a great way to do it like this; this way, you are always nice and systematic.0097

Galactose and mannose are both hexoses, so we have 1, 2, 3, 4, 5 and 6.0102

Let's make them a little big here.0110

OK, we have got OH, OH, OH, OH and CH2OH0114

This is going to be our alpha-galactose.0123

Actually, not alpha yet, it is just galactose because the alpha and the beta configurations are when they are actually in a ring.0127

So, you notice we have right, left, left, right, 1, 2, 3, 4; galactose is the c-4 epimer of glucose.0134

OK, this is our galactose.0143

Now, we are going to put it together with our mannose.0146

Again, we have a 6-carbon sugar, 1, 2, 3, 4, 5, 6; there we go.0149

We start with our aldehyde; let’s go ahead and put our CH2OH of the other end, and now, we can build what's in between.0156

This is going to, this is mannose, right?0162

OK, mannose is a c-2 epimer, so this is going to be OH, OH, OH, OH.0167

You notice the 2 on the left, 2 on there right; this is our mannose.0175

OK, now, let’s go ahead and draw the ring structure for them0181

And again, what you do is you take this linear structure which is vertical; you rotate it to the right, and then you bring this side around the back, and then you make a little bit of a rotation, so that the OH is actually pointing to the right and the CH2OH is pointing up, and you'll see what it looks like in just a minute, and when you put it together, you get the following.0183

Yes, so we have - let me, yes, that's fine - so this, this, this, like that, and we have the alpha-configuration, so this hydroxy is down.0209

This hydroxy is down; this hydroxy is up, and this hydroxy is up, and, of course, we have our CH2OH.0223

That is what we did; now, we have our alpha-galactose aGal.0231

And now, let's go ahead and do our mannose.0237

Again, rotate it to the right; bring this aldehyde down to the right.0240

Now, this CH2OH, bring it around back, and then rotate this carbon right here, the no. 5 carbon, rotate this one.0245

So, the hydroxy is pointing to the right, and the CH2 is pointing up.0254

That is the deconfiguration, and when you do that, what you get is the following.0258

I'll go ahead and do this one in red.0263

We will draw the general 6 carbons, and we said this is the beta-mannose, correct, beta-1.0266

Beta, this is going to point up, right?0273

And then, looks like this one is also going to point up.0278

That is this carbon, and then on this one is going to go - let me see, wait, now, I'm lost - this is going to be up; this is going to be up.0281

This is going to be up; OK, sorry about that.0293

This is no. 1 carbon, no. 2 carbon, no. 3 carbon, 1, 2, 3.0295

So, we have taken care of those, and now, we have this one; this hydroxy is going to be down, and this is CH2OH.0299

As you can see, it is very, very important to keep track of which carbon we are looking at; this thing can be very, very confusing, so all the more reason to do it nice and systematically0307

OK, this is going to be alpha-1, beta-1.0315

In blue, we are going to be connecting this carbon with this carbon.0320

What I'm going to do is, this mannose, in order to draw it out and bring this carbon in close proximity with this one, I'm going to have to flip this.0323

Now, there are 2 ways that I can flip this molecule; remember we talked about spin and flip?0330

I think flip is probably the best way to go.0336

It seems to be the one that you see more often in biochemistry text books as opposed to spin, but you realize, this is a flat molecule, right?0338

So, we have this right here; let me go ahead and draw, so you can see.0348

This is Haworth projection; this is a flat molecule.0352

You are looking at it like that; you can flip it two ways.0355

You can flip it that way, or you can flip it that way, right?0358

There are two ways you can flip something, either side to side or forward and back.0364

In this particular case, let me go ahead and do this in blue.0368

I'm going to go ahead and flip it, and what I'm going to do is, I'm going to flip it sideways.0373

In other words, I'm going to bring this carbon here, and I’m going to bring this carbon over there.0377

OK, so I'm going to flip it sideways, that way, not this way, forward back.0384

When I do that, it is the oxygen that tells me how the flip has happened.0390

This is the thing, wherever the oxygen is, that is what tells me where to put the other substituents- the hydroxys and the CH2OH.0394

So, when I do the flip, I end up with this ring structure.0402

Now, the oxygen is on the back left.0407

OK, and now, let’s see what it is that I've done.0411

This OH, now, this is the no. 1 carbon over here, 1, 2, 3, 4.0414

Now, the no. 1 carbon is over here, and this is the no. 4 carbon.0419

OK, let me go back to blue.0425

OH is down here; this OH is going to be up there.0429

These have been flipped, so now, these are both down- that hydroxide and that hydroxide.0433

This one has been flipped over to the other side, and it is also down, so this is going to be over here, CH2OH.0438

Now, that is the arrangement.0447

Now, we are going to put this thing and this thing, so this is beta mannose that has been flipped.0450

Now, we are going to put this together with this; we are going to connect this carbon with this carbon, and when we do that - let’s go ahead and just draw our little equilibrium arrows - our final product is going to look like this.0459

I am going to do this in black, actually.0478

We have that, and remember, we do our little arrangement like this except this time, the O is over here, like that.0481

We have this OH; we have this OH.0498

We have this OH; this is in standard configuration.0501

The oxygen is on the back right, and over here we have flipped it, so now, the oxygen is on the left.0504

That means this hydroxide is here; this hydroxide is here.0510

This hydroxide is here, and this CH2OH group.0514

It is always interesting to try to draw it; I will go ahead and put the H2 there and the OH, and there we go.0520

This is our Gal(alpha1)(beta1)Man.0526

There you go, nice and systematic.0534

Draw out the linear structure; rotate them.0535

Create the ring structures in standard configuration with the oxygen on the back right, and then decide which carbons you are going to have to connect, and then decide which one of those monomers you are going to have to flip.0538

OK, flip, it is up to you.0548

You can do a flip or spin, as long as the arrangement of the substituents is such that it is very, very clear what is where.0550

If you want, you can go ahead and add a little stereochemistry by doing that, darkening up some lines.0557

Let me do that; I personally do not.0564

I just sort of leave it like that, but, of course, your teacher might want you to actually demonstrate the projection by showing the darker lines.0568

So, there you go; that is it- nice, basic disaccharide0574

As long as you know the structures of the monomers, which I imagine your teacher is probably going to have you memorize, everything should be nice and straight forward.0578

OK, let’s start our discussion of polysaccharides.0586

I will go ahead and I am going to do this in blue.0591

Polysaccharides, now, we are just going to be adding a whole bunch of monomers, one after the other on a chain, just like we did with proteins, except those were amino acids instead of sugar units.0595

Polysacchs- they are also called glycans, and this glycan name will come up.0608

In case it does, it is not a different type of molecule; it is just another name for a polysaccharide.0623

Now, polysacchs, they differ from each other - there is a whole, whole, whole bunch of polysaccharides - with respect to 4 things.0628

The monosacch units that actually make up the polymer.0654

Which monosaccharide units are we using?0658

Are we using only glucose or are we using glucose and galactose and mannose and n-acetylgalactosamine?0659

Which monomers are we using?0668

Chain length, you might have a polysaccharide that is only 15 monomers long.0671

You might have one that is 150 thousand polymers long, so chain length.0675

And, if you have, let's say, a bunch of glucose that is 15 long and a bunch of glucose that is 1500 long, those molecules are going to behave differently, just because they are made of the same monomer, glucose, the length will actually change the chemistry.0682

Branching along the chain - I'm sorry, branching along the, well, yes, branching along the chain.0700

What you are going to have is something like this.0716

You are going to have some monomer going on, going on, and all of a sudden it is going to branch off like this, and maybe branch off again, and then maybe branch off again.0717

Polysaccharides will do that, and we will see some examples in just a minute.0725

And, of course, the last thing that they differ with respect to is the nature of the glycosidic bond connecting the monosaccharides.0729

In the example that we just did - monosaccharides, just let me go ahead and write this out - our connection here was alpha-1, beta-1.0751

This is the no. 1 carbon; this is the no. 1 carbon on the mannose.0762

So, and alpha-1, beta-1, well, maybe if I had an alpha-1, alpha-1 mannose, that is going to be an entirely different polysaccharide simply by virtue of the nature of the glycosidic bond.0765

Totally different, totally different chemistry, totally different folding- that is the whole idea.0775

Small subtle changes make huge differences because you are talking about big molecules, and when all of these things sort of add up, you get entirely different chemistry.0779

OK, define a couple of more terms.0780

A homopolysaccharide is exactly what you think it is.0798

It is a polysaccharide made of 1 type of monomer.0805

I'll just write "1 type of monomer makes up the chain".0810

In other words, it is just the same monomer one after the other, glucose, glucose, glucose, glucose, glucose makes up the chain.0819

That is a homopolysaccharide, and, of course, heteropolysaccharide, you have 2 or more; but for formality's sake, let's go ahead and write it down.0826

A heteropolysaccharide- 2 or more monomers make up the chain.0835

Maybe you have an alternating glucose, mannose, glucose, mannose, glucose, mannose.0854

That is a heteropolysaccharide; there happen to be 2 of them.0858

There can be more.0861

OK, now, polysaccharides serve lots of purposes.0863

What is really, really exciting is glycobiology, the study of carbohydrates, it is a fantastic, fantastic area of research right now because every single day, literally, every single day, some new polysaccharide, some new protein attached to a carbohydrate, is being discovered that serves a whole different purpose; and that is what's amazing about this.0869

Polysaccharides, they serve many purposes; and certainly, many of the purposes we haven't even discovered yet.0894

There is plenty of room for growth in this particular field, and polysacchs, interestingly enough, they have no specific molecular weight.0900

They have no specific molar mass.0919

In other words, we don't talk about a polysaccharide that has a molar mass of 50,346g/mol.0924

It is not that precise; it is not like proteins where you have a specific number of amino acids if you have 1 more or 1 less.0933

It is an entirely different protein for the most part.0940

Polysacchs, when they are synthesized, we talk about a polysaccharide that is roughly 25,000 monomers long, 300 monomers long, more or less.0943

There is no specific molecular weight.0954

OK, now, let's talk about some homopolysaccharides that serve as a fuel storage.0958

One of the purposes of polysaccharides is as a reserve fuel source if the organism is not actually taking fuel in.0965

In our case, we tend to store fuel as glycogen; that is our primary polysaccharide for animals.0974

For plants, it is starch, so homopolysacchs serving as fuel storage.0981

And, we are going to talk about starch, and we are going to talk about glycogen; and both occur inside the cell.0999

Now, starch and glycogen are actually the same thing; they are made of the same thing- glucose.1017

It is just the degree of branching, as you will see in a minute, that is going to differentiate the glycogen from the starch- an entirely different chemistry.1022

It is actually amazing.1028

Let's talk about starch first.1030

Starch has 2 types of glucose polymers.1035

Starch is made of 2 types of polysaccharide chain.1048

One of those is called amylose or amylose; however you want to pronounce it.1053

It is glucose monomers connected by alpha-(1,4) glycosidic bonds, just one glucose after the other with the connection as alpha-(1,4), alpha-(1,4), alpha-(1,4) all the way down the line in just a straight, single chain.1060

Now, the other particular polymer for starch is amylopectin, and it is also glucose connected by the alpha-(1,4).1085

It has that chain, but along that chain, there are branch points; and those branch points - and, alright - and branching by alpha-(1,6).1100

So, at the no. 6 carbon, that CH2OH sticking up, it actually branches off at that point, and it starts a whole new chain.1121

And then maybe along that chain, it branches again; and it starts a whole new chain, so that is the difference.1131

Amylose and amylopectin, and they are sort of intertwined; and again, you will see it in a minute.1136

We are going to do a detailed structure, and then, sort of a broader structure.1141

OK, now, let's see what else do we want to talk about before we actually start looking at some structure.1146

Ah, yes, so, we talked about reducing sugars, non-reducing sugars, there is a reducing end, in other words, a free anomeric carbon that can react, that can be oxidized by iron ion or copper ion.1154

There is a reducing end, so polysaccharides, polysacchs, have a reducing end and many non-reducing ends because of the branching.1172

And this idea of the non-reducing end, having many of them, is going to play a very, very important role in physiology as we will talk about at the end of this lesson.1198

OK, glycogen, just one quick word about glycogen, it is the same as starch.1208

OK, in other words, it has the amylose; it has the amylopectin, but it is more highly-branched, and more compact.1220

Again, totally different chemistry simply by virtue of the branching.1240

Amylopectin, it might branch off maybe every 30 to 35 glucose units, 30 units and then it will branch off, 30 units and it will branch off.1244

Glycogen might do 10 units branch, 10 units branch, 5 units branch, 7 units branch.1256

It branches more often, and it tends to be more compact, more dense.1262

That is it; that is the only difference between the 2, but the fundamental structure is the same.1267

Alpha-(1,4) glucose units and alpha-(1,6) glucose, glycosidic bond at the branch point.1271

OK, let's go ahead and take a look at some structures here.1281

In this particular case, I am going to be presenting them as illustrations instead of drawing them out by hand simply because we want to save a little bit of time, but now, I think we have a little bit of a sense of what the glucose looks like, what the monomers look like, alpha-1.1285

We just want to be able to identify what is what, what is connected to what.1297

Let's take a look at some pictures, and the first one we are going to look at is amylose.1302

OK, we have our amylose, and we said that we have alpha-(1,4) and its glucose.1310

So, we have 3 monomers of glucose, so it goes off in this direction.1319

It goes off in this direction.1321

Let me go ahead and use, yes, let me go ahead and stay with red here.1323

Here is our 1,4; this is our no. 1 carbon, alpha-configuration.1328

This is our no. 4 carbon on the other.1333

This is our no. 1 carbon, alpha-configuration, the hydroxy is down; and this is our 4 carbon from the other side.1336

This is it; this is amylose.1344

I don't think I'm going to have to...that is fine, I'll just go ahead and...not a problem.1348

This is our amylose chain, and it goes off this way, and it goes off this way.1351

Now, at the end, of course, this is your reducing end.1355

The polymer will usually go on in that direction connected to this hydroxy.1361

Let me go ahead and actually do that.1366

It will end up being connected to this hydroxy.1369

Here is the reducing end; this is the non-reducing end.1371

That is it- nice, basic structure.1375

Glucose units, down, up, down, CH2OH, CH2OH, oxygen is in the back right, oxygen back right, oxygen back right- this is a nice, good, very, very well-behaved polysaccharide.1378

We did not have to flip anything; we did not have to spin anything.1392

That is good; this is the Haworth projection that you see.1395

Now, of course, you know the hexose rings, they assume chair conformations.1401

They are not flat like this; they are not like benzene.1405

Benzene is a flat molecule, these are not.1408

I wanted you to see what this looks like in actual configuration, in actual conformation, I'm sorry, conformation.1410

These hexose rings actually assume chair conformations, and here is what the glycosidic bond looks like.1417

This right here is actually this right here.1425

So, we have our 1 and our 4 carbon, our 1 carbon, our 4 carbon, 1 carbon, 4 carbon, and, of course, it goes on like that.1429

You see this little stair step pattern, this is how it looks.1437

Now, again, it is going to be up to your teacher whether he or she wants you to draw it like this in this projection, or whether he or she actually wants to see at least 2 or 3 units in the chair conformation.1442

I will leave that up to your teacher, but again, what you want to notice is the arrangement, oxygen back right, oxygen back right; here is your CH2OH.1457

Notice, here, they actually wrote the C; here, it is just 2 lines coming together at a point, at a vertex.1466

So, that is a carbon; that is a carbon.1474

That is a carbon, nothing new here.1475

Equatorial, axial- that is what you have to watch out for.1478

OK, start with this projection, and then, go to this particular rendering, this particular representation.1482

OK, now, let's take a look at amylopectin.1490

I think that is going to be the next, yes; this is a little piece of amylopectin.1494

Let's go ahead and identify our 1,4.1499

So, we have our 1,4, 1,4 .1504

This is our glycosidic bond, glycosidic bond; and now, we have our 1 and 6.1507

There you go; that is your branch point.1514

At the no. 6 carbon of a particular glucose monomer, that oxygen has reacted with the anomeric carbon of another glucose, and it has started the chain, a second chain.1516

Now, this chain is going to go off in this direction, and then, this chain is going to go off in this direction; and they are going to parallel each other.1528

And, as you will see in a minute, they don't just parallel each other, they actually wind around each other in a helical pattern.1535

That is it; that is the only difference.1542

You have the 1,4 configuration, and in amylopectin, your branch points are at 1,6.1545

So, maybe a little further down the line, there is another 1,6.1550

That is it, alpha-(1,6).1555

This is alpha, because the hydroxy is pointing down.1558

There you go, and, of course, this is another representation of it with just a couple more.1562

Here, we have 3 and 1; here, we have 3 and 2.1569

You see our 1, our 4, our alpha-1, our 4.1572

This is alpha-1; this is our 6, and then, of course, it continues on.1577

This is alpha-(1,4), that is it.1581

This is amylopectin, nothing going on here; monomer, monosaccharide, disaccharide, now, it is polysaccharide.1585

What is important are the individual monomer units; if you understand those, you can build any polysaccharide you want.1592

That is the whole idea; that is what we want you to be able to do.1599

OK, so, now, let's take a look at...OK, here we go.1602

So, we talked about the actual amylopectin clusters.1610

This is amylopectin; this is a macroscopic.1615

We started over here; we have some chain, and then, this one branched off, and then it branched off again, and then it branched off again.1621

And then now, when the whole branching thing stopped, these 2 that were paralleling each other, now, they start to wind around each other in a coil.1628

What you end up with is, once everything is built, you end up with something that looks like this.1639

That is it; this is a nice cluster of amylopectin.1645

That is all.1649

This, right here, this is a detail of those 2 strands.1650

Once it branches off in the 1,6, they parallel each other, they actually start to wind around each other, so this is 1 strand, and this is another strand, and they intertwine.1653

That is it; they intertwine.1666

There is nothing in between them; they just intertwine.1668

It is like the backbone of the DNA, a nice helical pattern, and that is represented here.1671

Let me just write, this is an amylopectin, helix.1678

That is it, nothing strange happening here.1685

OK, let's actually, let's draw something by hand; let’s see.1690

Again, we want as much practice as possible.1698

Let's draw an alpha-(1,4) and an alpha-(1,6) of amylopectin just for a little practice.1705

Pretty much what we just saw, let's just draw it out by hand, so we know where to put everything.1718

OK, let's do our glucose down here.1728

Let's go 1,4.1733

This is going to be alpha-(1,4), so it is going to be like this, like that.1740

This is our 1,4 linkage, so this is alpha-1, and this is 4.1749

Let me go ahead and put that there, this, there, this, there, here.1755

I have got the CH2; this is going to be my 1,6.1763

Let me go ahead and put this as CH2OH.1767

OK, 1,6, this is the no. 6 carbon.1771

Let me use black.1776

This is our no. 6 carbon, and now, this is going to be connected to a - go back to red - another alpha-(1,6).1780

Alpha means that the hydroxy is below the ring.1794

It is going to look like this, and, of course, this is - nope, that is not there - this is glucose, so this is down.1798

This is up, and this is going to be off connecting that way, and chances know what, I am going to go ahead and connect this one off too.1809

This is going to go that way, and that is going to be running off, and then, this is going to be CH2OH.1824

There you go; here, we have our nice amylopectin branch point, glucose, alpha-(1,4), glucose, alpha-(1,6).1831

This is the alpha-1; let me go ahead and erase these and write them in black.1843

This is the alpha-1, and this is the no. 4.1851

That is it; there should be no problem at this point.1855

Hopefully you have had a little bit of practice, and you should be able to just knock them out given the particular configuration at the glycosidic bond.1857

OK, let's see what else we can do.1866

OK, now, let's talk a little bit about glycogen.1871

Let me go ahead and...a page here.1874

Now, glycogen, let's see, you haven't eaten for a certain number of hours, and your body needs some energy.1878

Well, if your body doesn't have any energy in terms of the food that you put into it, it is going to go to its next readily available source of energy, and that is the glycogen that is stored in your cells, that is stored in your body, mostly in your liver.1892

That is the first place that it is going to go in order to break off glucose units and send those glucose units into the bloodstream and out to the other parts of the body, so that your body and brain can function.1907

That is it; glycogen is essentially just a readily available, very quick storage for available fuel that gets it into your body right away.1920

Glycogen is hydrolyzed - in other words, it is broken up - from the non-reducing ends, the left ends.1934

Remember we had that little cluster; well, I will draw it out in just a minute.1957

OK, now, since - excuse me - there are so many branches and we said the glycogen is more heavily branched than starch, several glucose monomers can be cut off simultaneously in order to supply the body with glucose, with individual glucose monomers.1962

Now, let's go ahead and draw what that looks like.2016

Let's do a little bit like a main chain, something like this.2019

So, I have got another branch here, maybe another branch, another branch, another branch, another branch.2024

I'm just going to draw a whole bunch of branches like this, like that, like that, like that.2030

Each one of those, at some point, it terminates; and what you have are these, you have glucose at the ends.2036

These are the non-reducing ends right here; of course, it is a lot more compact than this.2044

This is the reducing end right here; this is the reducing end.2049

Now, when your body needs glucose, glycogen has evolved to take on this particular structure because what it can do is, once it needs the glucose, it can just go and cut off these individual ones.2054

Instead of one long chain, where it has to go cut this one, then this one, then this one, then this one, then this one, then this one, it is going to take a certain amount of time.2070

Yes, enzymatic reactions are very, very quick, but still, it is going to take a certain amount of time; but if it can take a whole bunch of these off simultaneously, hundred of thousands of them, millions of them, and just deliver them into the body, for the time it takes to cut off one, well, it can cut off several hundred thousand, and deliver them into the body.2078

That is why glycogen has the structure that it has, highly branched, so it has a whole bunch of glucose monomers available to it all at once because you are going to need that fuel all at once.2100

That is what's happening.2113

OK, now, let's talk a little bit more about glycogen and concentration, glycogen, which is stored as insoluble.2115

That is the key word here, insoluble granules, and there is probably a picture of it in your book.2135

You will see a cell with the little dots, the little black dots.2141

Those are granules of actual glycogen, granules in the cytosol.2146

Cytosol is the intracellular fluid.2154

OK, so, glycogen which is stored as insoluble granules in the cytosol - excuse me - contributes nothing to the osmolarity of the cytosol because it is insoluble, it is solid.2158

In other words, it doesn't have, there aren't free particles of glycogen floating around in an aqueous environment; it is not dissolved.2182

Now, liver cells store glycogen equivalent to about 0.4M free glucose.2193

In other words, if I were to take all of the glucose, all of the glycogen, and break it up into individual monomers, the amount of glucose that is there actually accounts for about 0.4M because glucose is soluble; glycogen is not soluble.2218

Now, if glucose were stored as monomers, just sort of floating around in the cytosol, the osmolarity of the cytosol would go through the roof.2234

The osmolarity of the cell, well, 0.4M, the osmolarity, there are going to be so many more particles inside the cell than outside the cell.2265

It is going to cause the liquid to flow from outside the cell into the cell causing the cell to burst open.2281

OK, it caused fluid to flow into the cell and rupture it.2289

The body definitely knows what it is doing; it needs to have a supply of glucose, but it can't just have free glucose floating around in the cell, in the cytosol because then, the osmolarity of the cell would be so high that it would cause a difference in osmotic pressure inside and outside.2309

Osmosis would pull water into the cell, and the cell would just explode.2326

So, by storing it as insoluble glycogen, it is there.2332

It is insoluble, so it does not contribute anything to the osmolarity, but it is readily available; and the particular form of glycogen as such that all of those glucose monomers are available very, very quickly- fantastic, absolutely fantastic, extraordinary molecule, extraordinary molecule.2337

That is what's going on with glycogen and starch.2356

OK, thank you for joining us here at Educator.com2360

We will see you next time, bye-bye.2362