Biochemistry Disaccharides

Hello and welcome back to Educator.com, and welcome back to Biochemistry.0000

Today, we are going to start talking about disaccharides, putting 2 monosaccharides together in something that is called a glycosidic bond.0004

Let's go ahead and get started.0013

Alright, let's see how can we do this.0016

A disacch is exactly what it sounds like.0020

CCH, I always forget how to write that.0028

Disacch is made of 2 monosacchs joined covalently- actually, you know what, let me just - joined by a covalent bond called an O-glycosidic bond- very, very, very important bond in biochemistry.0033

The hydroxy group of 1 sugar has reacted with the anomeric carbon of the other sugar.0083

Now, when we say the hydroxyl group of 1 sugar, the truth is, it can actually be any of the hydroxyl groups; but in general, it is going to be specific hydroxy groups that are going to react with the anomeric carbon of the other sugar.0127

Again, you will see from the bond, which particular hydroxy is going to react; but it actually can be any one of them.0143

OK, let's just go ahead and do examples of these.0151

We will just go through several examples to get a sense of how to put the structure together, how the bonds are drawn, the perspective drawings that we are going to be using, and how we are going to name them systematically.0155

That is what's important.0168

Let's do examples of disacchs and how to name them systematically.0172

OK, let's go ahead and start with a particular disaccharide.0189

Let's start with alpha-D-glucose, and connect it to beta-D-glucose in something called a 1→4 connection.0193

OK, let's go ahead and draw out our alpha-D-glucose.0200

Again, always proceed systematically.0206

Start with your basic unit.0209

Alpha-D-glucose, we are looking at this thing right here.0212

God, I really love the blue; I think it is my favorite.0215

OK.0218

CH₂OH, this is alpha-D-glucose.0222

And now, we are going to be joining it with - I'll go ahead and put a little plus sign here - beta-D-glucose.0231

Let me draw out the beta-D-glucose first, here.0238

Beta is going to be up here, but everything else is the same because we are talking about glucose, so CH₂O₄.0244

OK, now, when we put this and this together - let me go ahead and do a red - I'm going to number my carbons.0255

This is no. 1, no. 2, no. 3, no. 4, no. 5.0263

And again, 1, 2, 3, 4, 5, I'll go ahead and put 6 too; it is not a problem0270

And again, standard position, oxygen is in the back right; the anomeric carbon is on the right.0276

That is the reducing end of the sugar; this, over here on the left, is the non-reducing end of the sugar.0281

In this particular case, let me go ahead and write, so this is beta-D-glucose.0287

Again, there is a bunch of hydroxys here that can actually react with this anomeric carbon.0296

In this particular case, we are going to form a 1→4 connection.0301

The anomeric carbon, the no.1 carbon, is going to be connected to the no. 4 carbon; and here is the reaction that is going to take place.0306

This is a condensation reaction.0316

In other words, the elements of water are going to be taken away from this, the elements of water that we are going to be taking away right there.0318

This hydroxy on the anomeric carbon is going to go away, and this hydrogen connected to the oxygen on the no.4 is going to go away.0329

So, the oxygen that is going to go between this unit and this unit, actually belongs to this carbon, the no.4 carbon.0338

What you end up with is the following.0347

Let me go ahead and draw a couple of arrows, one this way and this way; and if we go this way, we are actually losing water.0350

If we come this way, we are actually adding water, so this is a hydrolysis.0358

When you hydrolyze a disaccharide, you get 2 monosaccharides.0363

When you condense 2 monosaccharides, you are getting the disaccharide.0366

OK, this is how it is going to look.0370

I'll do this one in red, boom, boom, boom, boom, boom.0374

OK, I'll go like this, and up like that; and then I've got that, that, that, that, that, that.0380

OK, this is the beta, and now, I'll go ahead and fill in my rest.0389

This is up; this is down.0395

This is CH₂OH; this is down.0400

This is up; this is involved in the bond.0404

This is CH₂OH.0407

OK, this particular sugar is called maltose.0410

Maltose- this is the common name.0416

In the sugar, maltose, what has happened is that an alpha-D-glucose has reacted with the beta-D-glucose.0422

The anomeric carbon has reacted with the no. 4, with the hydroxy on the no. 4 carbon, to create this right here.0430

This right here, this is your O-glycoside bond.0440

OK, that is your O-glycoside.0446

O, because the O is involved; and notice, down, down.0447

That is why it is drawn this way.0453

This is how we actually represent the arrangement in space, but we keep this particular perspective, so that we see how the molecules, how the individual units are arranged.0456

This is how we do a disaccharide.0466

OK, the name for this is alpha-D - because it is a polymer - glucosyl, the first (1→4)-D-glucose.0469

Alpha-D-glucosyl, that is the first monomer arranged in a 1→4 pattern.0495

One on the left connected to the no. 4 carbon on the right- that is where this 1→4 in parentheses means, and a little arrow going from the 1 to the 4.0502

We go from left to right- D-glucose.0509

OK.0512

I should actually write this as...because we have actually specified the stereo chemistry on this particular monomer, it is the B.0517

This is beta-D-glucose.0525

Now, there is a slightly longer name, but we are actually going to be dealing with a shorter name.0529

I'm going to write the longer name, but then we are going to exclusively start dealing with the shorter name.0533

This is also called - and I'm not going to draw out the structure again, you can just flip back - alpha-D-glucopyranosyl.0539

Remember, pyranose, 6, gluco, pyro, glucose pyranosyl- it is a little redundant, but you will see it, pyranosyl(1→4)-beta-D-glucopyranose.0553

Now, obviously, you can't use something like this, so here is the shortened version.0574

All of the sugars just like the amino acids, they have 3-letter shortcuts for them, like Ala is alanine.0580

Well, in this particular case, glucose is Glc; and there is list in your book of the 3-letter shorthand notation for all of the individual sugars, galactose, glucose, ribose, deoxyribose, whatever it happens to be.0588

In this particular case, the name is going to be written this way: Glc for glucose.0605

We write the configuration at the carbons that are attached by the O-glycoside bond.0614

The 2 carbons that are involved in the bond, we give their configurations: alpha 1 to 4.0620

The fourth carbon, we don't do alpha-beta because the alpha-beta designation is only for the anomeric carbon.0635

Alpha(1→4)-beta-Glc, also written as Glc-alpha(1→4)Glc.0641

Often, the monomer on the right, the fact of the matter is, well, I'll tell you in just a second why it is I wrote beta here and not there.0654

Let me go ahead and tell you what is going on.0667

This does not mention the beta explicitly on the second monosacch because something called mutarotation, it often switches the configuration.0670

Even though, we know that we use the beta version of the second monosaccharide, the fact of the matter is, the alpha and beta forms, they actually often switch.0712

So, the stereo chemistry on the reducing end of the sugar, the one that has the free anomeric carbon, it is often unspecified.0722

Sometimes, you don't necessarily have to put the beta there; it is not a problem, unless, specifically, they want you to.0730

In this particular case, we put together an alpha-glucose with a beta-glucose, and what we ended up with is Glc, glucose, alpha-1 configuration at the anomeric carbon connected to the no. 4 carbon, the hydroxy on the no. 4 carbon, and the other disaccharide was a glucose.0736

That is all that happens- switches the alpha-beta-configurations.0755

Again, either one of these is fine.0764

If you want to specifically write the beta, that is fine; if not, you are not going to have any points taken away.0765

OK, now, again, as I said, if the anomeric carbon on the second monosacch, in other words, the one on the right, on the monosacch is free like it was with maltose, then this is called the reducing end of the sugar because now, you have a disaccharide, which happens to be a reducing sugar.0770

Fe³⁺ of Cu²⁺ will still oxidize that end.0815

It is available to be oxidized; it isn't always the case.0820

In a minute, you will see an example of something that is not a reducing sugar, a disaccharide; but this one, because the anomeric carbon, that hydroxy was not involved in the O-glycoside bond, it is still free, it is a reducing sugar.0823

It is called the reducing end.0839

And again, we have a reducing sugar.0845

Let me read that again.0855

If the anomeric carbon on the second monosaccharide is free, then this is called the reducing end; and again, we have a reducing sugar.0857

And, of course, the other end, the one on the left, the one that cannot be oxidized, that is the non-reducing end.0864

OK, maltose, what we just did, is a reducing sugar.0870

Maltose is a reducing sugar.0880

OK, now, as we said, any of the OH groups on the second monosacch can react with the anomeric carbon of the first monosacch - OK, excuse me - even the hydroxy on the anomeric monosacch, even the OH on the anomeric C.0885

Let's look at an example.0943

OK, now, let's go ahead and look at the sugar trehalose.0946

Let's look at the disacch trehalose.0958

OK, let's see what we have here.0964

Now, trehalose, we are going to have an alpha-D-glucose and an alpha-D-glucose that are going to be connected by their anomeric carbons.0966

Let's go ahead and draw the alpha-D-glucose.0974