Biochemistry Polysaccharides

Hello and welcome back to Educator.com 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 be...no, 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