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Lecture Comments (4)

1 answer

Last reply by: Professor Hovasapian
Wed May 14, 2014 1:33 AM

Post by Sitora Muhamedova on May 12, 2014

love your lectures!

1 answer

Last reply by: Professor Hovasapian
Wed Sep 4, 2013 11:57 PM

Post by Donna maria on September 4, 2013

thank you for the brilliant lecture. may i ask why there were 8 L and 8 D as out of the 4 chiral carbons, i only spotted 3 that consisted of OH located to the right? Therefore, I know i have missed something important or not grasped the true concept? in my head, i see 12 to right and 4 to left?  


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
  • Monosaccharides 1:49
    • Carbohydrates Overview
    • Three Major Classes of Carbohydrates
    • Definition of Monosaccharides
  • Examples of Monosaccharides: Aldoses 7:06
    • D-Glyceraldehyde
    • D-Erythrose
    • D-Ribose
    • D-Glucose
    • Observation: Aldehyde Group
    • Observation: Carbonyl 'C'
    • Observation: D & L Naming System
  • Examples of Monosaccharides: Ketose 16:54
    • Dihydroxy Acetone
    • D-Erythrulose
    • D-Ribulose
    • D-Fructose
    • D-Glucose Comparison
    • More information of Ketoses
    • Let's Look Closer at D-Glucoses
  • Let's Look At All the D-Hexose Stereoisomers 31:22
    • D-Allose
    • D-Altrose
    • D-Glucose
    • D-Gulose
    • D-Mannose
    • D-Idose
    • D-Galactose
    • D-Talose
  • Epimer 40:05
    • Definition of Epimer
    • Example of Epimer: D-Glucose, D-Mannose, and D-Galactose
  • Hemiacetal or Hemiketal 44:36
    • Hemiacetal/Hemiketal Overview
    • Ring Formation of the α and β Configurations of D-Glucose
    • Ring Formation of the α and β Configurations of Fructose
  • Haworth Projection 1:07:34
    • Pyranose & Furanose Overview
    • Haworth Projection: Pyranoses
    • Haworth Projection: Furanose

Transcription: Monosaccharides

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

Today, we are going to start our discussion of carbohydrates, of sugars, otherwise known as saccharides.0004

Today we are going to talk about monosaccharides- absolutely fantastic, fascinating area of biochemistry.0011

I personally, I can't decide which is more exciting.0018

I love proteins, and then when we start doing sugars, carbohydrates, I love carbohydrate chemistry, and then when we talk about lipids, when we talk about enzymes, each area is more fascinating than the next; and it is amazing when all of this starts to come together.0021

Anyway, let's just jump right on in and see what we can do.0038

I have to warn you, there are going to be lots of structures being written out.0042

And again, I don't use pictures; I like to draw everything out.0047

My recommendation, again, I can't stress it enough especially for carbohydrates, because you have lots of carbons and lots of hydroxys.0051

It's one thing to be able to look at an illustration, and by all means, you definitely want to use your book.0060

Your book has fantastic illustrations of most of these things that I'm going to be drawing, but being able to say "Yes, I can see what is going on." is very different from being able to actually produce what is going on with your hand.0065

You want to draw these things out as many as possible, and you'll discover that just by the time you draw your fifth or sixth one, you have a really, really good command of the structures.0079

So, by all means, pictures are great, illustrations are great, but you have to be able to do it with pencil and paper.0090

You have to be able to do it with your hand.0095

OK, enough said; let's jump on in, and hopefully I don't make mistakes, because again, there is lots of carbons and oxygens and hydrogens that are going be floating around.0098

OK, monosaccharides.0109

Well, let's talk about carbohydrates first in general.0110

Carbohydrates are nothing more than aldehydes and ketones with several hydroxy groups attached to the non-carbonyl carbons.0114

That is it, or carbohydrates yield these things; they yield these aldehydes and ketones upon hydrolysis.0163

Do you remember when the lesson, when we did the example problems for peptides and proteins, we talked about glucagon; and we talked about how it induces the liver to actually break up glycogen to release free glucose into the blood?0197

Well, glycogen is a carbohydrate when you hydrolyze it.0212

When the liver hydrolyzes it, it actually releases free glucose, which is the monosaccharide.0215

So, carbohydrate is just that.0222

It's either the monosaccharide itself or the aldehyde or ketone, or it produces those things when you have actually hydrolyzed it.0225

That is all a carbohydrate is.0234

It's either an aldehyde or a ketone that has a bunch of OH groups attached to the other carbons; and you'll see the structures in just a second.0235

OK, most carbohydrates have the empirical formula CH2O.0245

That's where the name comes from- carbohydrate.0266

Hydrate for the H2O, carbo for the C.0269

That's the empirical formula.0273

Now, some carbs - I'll just call them carbs - contain nitrogen, sulfur, or phosphorus.0276


Now, there are 3 major classes, if you want to call them that; I mean, probably not necessary, but we tend to break them up like this.0290

There are 3 major classes of carbohydrates.0299

We have the monosaccharides, which we are going to talk about today, and saccharide just means sugar, the oligosaccharides, and the polysaccharides- long words.0307

Saccharide just means sugar; mono means 1 sugar unit.0335

Oligo means a few sugar units, and poly means a whole lot of sugar units attached to each other.0338

OK, monosacchs are the simple sugars, and consist of single aldehydes and ketones with those additional hydroxy groups attached to the carbons that are non-carbonyl- OH groups.0405 OK, let's go ahead and draw some structures out; let's do some examples.0345

Examples of monosaccharides- I'm going to do a lot of these.0410

OK, there is going to be a lots of structures.0413

I want you to see them over and over again until they are just completely natural for you.0416

OK, let's go ahead and do blue, because I like blue.0422

We have examples of monosacchs, and these are going to be the, I'm going to do the aldehydes first, and they are called aldoses.0430

Aldose, D-O-S-E - that just means carbohydrate, sugar; that is the ending.0442

Glucose, mannose, galactose- they all end in O-S-E.0447

Aldose means all the sugars that are aldehydes that is a broad class.0452

Examples of monosacchs, the first one I'm going to do is one that you've already seen before.0457

It is 3 carbons; I will do the aldehyde group up here, and I think I'll put the H on...that's fine, I'll go ahead and put the H on this side: CH2OH, and I will do the OH on this side, and H.0463

This is 3 carbons; this is the diglyceraldehide.0482

You have seen this one before.0485

Remember when we were talking about protein configuration, L-glyceraldehyde and D-glyceraldehyde?0492

Remember the L-glyceraldehyde had the hydroxide on the left?0498

The D-glyceraldehyde has the hydroxide on the right.0500

That is it.0505

The glyceraldehyde, it is a 3-carbon sugar, because it has 3 carbons.0507

The carbonyl carbon is the first.0513

This is the second; this is the third.0515

Notice, hydroxy attached to the second carbon, hydroxy attached to the third carbon.0517

Also notice that his one has 4 different groups attached to it.0524

So, this carbon is actually a chiral carbon center, but we know that already because of the glyceraldehyde.0527

We have a D; we have an L.0533

Those are the enantiomers of glyceraldehyde, the D and the L.0535

OK, that is a 3-carbon sugar.0540

Well, let's go ahead and do this one.0543

Let's do C, O, H, oops let me draw the backbone first, always a good idea.0547

H2OH, do the aldehyde first; do the last one.0555

Put the H2OH on there, and now, just go ahead and attach the hydroxys.0558

An hydroxy over here, and a hydroxy over here, we will put an H.0563

We will put an H, and this is D-erythrose.0567

And again, these are just examples; you don't have to know all of these.0572

There is only a couple that you are going to have to know.0575

Well, you are certainly going to have to know the glucose, and maybe galactose and mannose, but don't worry about that.0577

I just want you to get comfortable with what's going on here and how these are drawn.0583

This is a 4-carbon sugar.0587

1, 2, 3, 4, hydroxy, hydroxy, hydroxy, attached to the non-carbonyl.0591

This is the aldehyde group, the carbon double-bonded to the oxygen, hydrogen.0598

Carbon, double-bonded oxygen, hydrogen.0603

That is it; nothing actually changes.0605

The chain just gets longer; that is all that's going on here.0607

OK, let's go ahead and do a...this is 1, 2, 3, 4, let's do a 5-carbon sugar.0610

This is going to be 1, 2, 3, 4 and 5.0620

I go ahead and put my aldehyde group up there.0625

I go ahead and put that down here, and then, I go OH, OH, and OH.0628

This is the, 1, 2, 3, 4, 5; yes, this is D-ribose.0639

This is a 5-carbon sugar.0648

OK, now, let's go ahead and do a 6-carbon sugar- probably our most important one.0654

Well, not probably- our most important one.0659


Actually, you know what, let me go ahead and put the Hs here.0665

And again, if you ever see a carbon that is missing a bond, the last bond is going to be an H.0669

Sometimes I forget the Hs, sometimes I don't.0676

Anyway, 1, 2, 3, 4, 5, and 6, let me put the aldehyde group up there.0680

Let me put my H2OH up here.0692

Now, glucose happens to be OH here, OH here, OH here, and OH here.0694

This is D-glucose.0703

This is a 6-carbon sugar.0709

OK, now, let's make some observations here.0713

All have aldehyde groups.0717

They are called aldoses.0731

These are all aldoses because they have the aldehyde, aldehyde, aldehyde, aldehyde.0736

Notice, the only thing that happened is the chain got longer.0744

That is that.0749

The carbonyl carbon, the carbonyl-C, is no. 1.0751

So, 1, 2, 3; this is 1, 2, 3, 4, 1, 2, 3, 4, 5 carbon.0758

This is the 1 carbon, the 2, the 3, the 4, the 5, and the 6 carbon.0767

OK, here is the important part.0774

Again, as with amino acids, the DL system applies.0778

In other words, the reference carbon, the reference C, is the chiral carbon furthest from the carbonyl carbon.0797


If its configuration, I should say if its configuration matches D-glyceraldehyde, then the monosacch is a D-monosaccharide.0832

It is a D-sugar; it is a D-aldose.0858

There we go.0866

So, the reference carbon in this particular case, we are going to be looking at the chiral carbon that is furthest from the carbonyl carbon, and we are going to check to see whether the hydroxide is on the right for D or on the left for L.0868

That is why if you notice, in this particular case, this right here, let's look at the D-glyceraldehyde; this is our reference molecule, so let's not worry about that.0883

This is the chiral carbon; this is our reference.0891

This configuration, if it matches this configuration, the reference carbon for the others, that is what's going to designate it as D or L.0894

In this particular case, here is our carbonyl carbon; this is chiral.0901

This is chiral; this is not chiral.0905

It has 2 of the same thing attached to it- 2 Hs attached.0907

This is not a chiral carbon.0911

So, this is our reference carbon.0913

Well, reference carbon, the hydroxide is on the right hand side.0914

It matches the hydroxy on the right hand side of D-glyceraldehyde; that is what makes it a D-erythrose.0918

If I took this OH and this H and switched positions, put the OH on the left and the H on the right, then it would be L-erythrose because it would match L-glyceraldehyde.0924

In the case of D-ribose chiral carbon, third is a chiral carbon, fourth is a chiral carbon, fifth is not, so this is our reference carbon, sure enough, hydroxys on the right.0935

Notice, on all of these, the hydroxy on the last chiral carbon, the one that is furthest away, is all on the right.0947

Glucose, second is chiral, third is chiral, fourth is chiral, the fifth is chiral, the sixth is not chiral, so this is the reference carbon.0953

The hydroxy is on the right; it makes it D-glucose.0963

If the hydroxy were on the left as written in the Fischer projection, these are still Fischer projections, it would be L-glucose.0965

Notice, these others, I can put these anywhere, and I'll get the other isomers, but we will talk about that in a minute.0973

These are just some examples.0980

What we want to realize here is again, look for the chiral carbon that is furthest from the carbonyl, that is the reference carbon.0982

The configuration at that carbon is the one you compare to glyceraldehyde to see whether it is D or L.0990

We are going to be dealing with D-sugars exclusively, physiologically- D-sugars.0999

Just like for proteins, physiologically, there were L-amino acids, but for sugars, the body uses the D-monosaccharides.1003


Let's go ahead and look at some other examples of monosaccharides, but this time let's do some ketoses, the ones that have ketones- draw out their structures.1016

Let's go ahead and do this in, I think I'm going to do this one in black.1026

We have examples of monosacchs, and this time, we are going to do the ketoses.1033

And again, ketose, they have a ketone group in them- all of them.1043

This is a general class.1046

Well, let's look at the 3 carbon.1049

We have 1, we have 2, we have 3, OK.1052

Because this is a ketone, the first carbon is not going to be the carbonyl carbon; it is the next one.1055

This goes here; this is going to be CH2OH, and this is going to be CH2OH.1063

This is called dihydroxyacetone.1071

The only difference between this and the glyceraldehyde is that now, the carbonyl is not on the first carbon, and the second carbon does not have the hydroxy; they have switched places.1080

The hydroxy now goes on the first carbon, and the carbonyl drops to the second carbon.1091

That is going to be the pattern of ketoses.1095

This is still labeled, though, first carbon, second carbon, third carbon.1098

Now, the carbonyl is always going to be on the second carbon of the ketose.1104


Let's go ahead and go back to black; let's do a 4 carbon here.1112

We have 1, 2, 3, 4; we said the carbonyl is on the second carbon, so let's put that there first.1116

Let's put RH2OH here, and there is an H2OH here.1125

Let's go ahead and stick a hydroxy on the right over there.1132

This is going to be, and let me go ahead and make sure I have my Hs.1136

These are the ones that I always tend to forget, and I also have a really, really bad habit, sometimes, of attaching an H to the carbonyl carbon.1141

Sorry, I hope you are catching those.1150

You have to be really, really careful with these structures; there is a lot floating around.1154

It is not hard; it is just detailed.1158

This is D-erythrulose.1161

And again, the carbonyl is on the second carbon, the hydroxide has gone up to the first carbon.1168

Now, this is the hydroxide; the only chiral carbon in this one is this one right here in this particular case.1174

Again, we have first, second, third, fourth; the second carbon is the carbonyl for ketoses.1180

Let's go to black; let's do the 5 carbon.1190

1, 2, 3, 4, 5, we'll put the carbonyl there.1193

We will put the H2OH here; we will put the H2OH here.1201

We want to set up our frame.1206

Now, let's go ahead and put, yes, let's leave the hydroxys on the right.1209

We have an H, and we have an H.1215

This is D-ribulose.1217

Now, know that the reference carbon is still the same.1223

The reference carbon is the chiral carbon that is furthest from the carbonyl.1225

In this particular case - I'll do this in blue - here, the reference carbon is this.1229

Hydroxy is on the right; that is what makes it D.1235

Here, this is a carbonyl; this is chiral.1238

This is also chiral; this is not chiral.1240

This is the furthest carbonyl; hydroxy is on the right.1244

That is what makes it D.1247

So, that part is still the same; you are still looking for the chiral carbon that is furthest from the carbonyl, comparing that, checking the configuration against glyceraldehyde.1248

And again, we are going to be dealing exclusively with D-sugars of the hydroxyl, and that carbon is always going to be on the right.1258

The other hydroxys, left or right, so the other ones might change.1265

OK, now, let's go ahead and do a 6 carbon.1270

Let's go back to black.1275

We have 1, 2, 3, 4, 5, 6; put the carbonyl there.1276

Put our H2OH here, H2OH on the last one.1285

Now, let's go ahead, and as it turns out, in this particular case, I'm going to go OH, OH.1290

And again, these are just examples; OH, H, H.1300

Now, you are probably wondering why it is that I put this particular OH here, and I left these.1310

Well, you remember, when I did the D-glucose, well, actually, you know what, don't worry about that.1315

Remember, we said the chiral carbons, so first of all, let's list the reference carbon.1323

That is chiral; that is chiral.1330

That is chiral; that is not chiral, so this is our reference carbon; hydroxy is on the right.1333

This is D-fructose, and again, this is the first, the second, the third, the fourth, the fifth, and the sixth.1338

Now, this one we leave alone; these 2 hydroxys, I can actually put them anywhere I want.1349

I can be left, right; this one can be left, right.1355

So, there are 4 possibilities: both left; both right; this left, this right; this right, this left.1359

And again, those sugars do exist.1366

I'm just drawing out examples for the sugars that we tend to run across the most often.1368

That is why I did D-glucose, and here, D-fructose, which is fruit sugar.1373

There is no reason why I put this hydroxy on the left and this hyrdoxy on the right other than the fact that this is the one we are going to run across most often.1381

The other sugars, the other isomers, do exist; and we will draw them out.1391

Don't worry about that, but again, these are just examples.1394

OK, now, let me go ahead and I'm going to draw out the glucose for comparison.1398

This is C, C, C, C, C, C, glucose, the aldehyde.1403

The carbonyl is on the first; let me go ahead and put this here, and we have OH, OH, OH, and OH.1411

This is D-glucose1423

You notice, the only thing that has changed is, the carbonyl has come from this carbon- red.1426

1, 2, 3, 4, 5, 6 - excuse me - the carbonyl has gone from the 1 carbon to the 2 carbon, and the hydroxy has come from this carbon up to this carbon; but notice, everything below that happens to be the same.1435

This structure is all the same; that is the only thing that makes D-fructose and D-glucose different.1461

They have different chemistry; they behave differently, but that is it.1468

That is all that's happened here.1471

On the aldoses, the no. 1 carbon is the carbonyl.1473

On the ketose, the no. 2 carbon is the carbonyl, but the numbering is still the same- this way.1476

OK, just wanted you to see what it is that actually happened here.1481


Let me actually write that down.1490

For ketoses, the carbonyl carbon, the carbonyl C is no. 2; and the reference carbon is still the chiral carbon, the chiral C furthest from the carbonyl.1496

That is the reference C for that one; that is the reference C for the glucose.1527

OK, I hope this is starting to make sense.1533

Again, we are just concerned with some structures here.1536

Let me go back to blue actually; there we go.1547

Let's take a closer look at D-glucose.1555

OK, let's draw the structure again: C, C, C.1564

You can never draw it enough times, trust me on this one.1567

C, C, C, 1, 2, 3, 4, 5, 6, carbonyl goes there; let me put that there.1569

Let me put H2OH here; it is right, left, right, right.1576

That is the pattern for D-glucose.1585

Once you actually draw in the carbonyl on the first carbon, then you put the hydroxy on this last carbon, the H2 which is not chiral, your pattern for the chiral carbons is right, left, right, right, so D-glucose.1586

So, D-glucose1599

And again, there are hydrogens here, but I did not put the hydrogens.1602

That is fine; I'll leave them off, but just know that there are...well, that's OK.1607

That is fine; I'll just put them in.1610

It is probably a good idea.1611

I should not leave them off.1613

OK, alright.1615

Now, notice, it has 1, 2, 3, 4 chiral centers.1617

It has 4 chiral centers, chiral carbons.1626

OK, because it has 4 chiral carbons, it has a total of 24 stereo isomers.1638

Remember what we said.1652


Well, let me say, in general, n chiral centers means 2n isomers- stereo isomers.1659

In other words, I have 4 chiral carbons.1684

That means I have 24, which is - 2 times 2 is 4, 8 and a 16 - I have 16 possible ways that these hydroxide, this 1, 2, 3, these 4 hydroxides can arrange themselves on these carbons.1688

This does not change; this does not change, but here, the hydroxy can be left to right, left to right, left to right, left to right, all right, all left, couple left, couple right, 1 left, 3 right, 1 right, 3 left.1704

All of those combinations contribute to the 16 isomers.1720

D-glucose happens to be one of those 16- that's it.1725

In this particular case, it is the one where you have, on the no. 2 carbon, 2, 3, 4, 5, 6, where the arrangement is the 2 carbon is on the right.1728

3 carbon is on the left; 4 carbon is on the right, and 5 carbon is on the right- that's it.1741

This is one of the 16 stereo isomers for this particular hexose.1745

OK, hexose, 6 carbons, just add that OS.1751

We also speak of pentose, tetrose, triose when we are talking about the number of carbons.1755


Of these 16, 8 are D-hexoses.1763

In other words, they are D in the sense that this final thing, the hydroxy, is on the right.1773

It matches D-glyceraldehyde, and 8 are L-hexoses.1779

In other words, this hydroxy on the reference carbon is on the left.1791

And again, hexose just refers to the number of carbons- that's all.1796

Hexose is just another general.1812

So, the breakdown would be something like this.1815

An aldose, that is the general, aldehyde.1820

Of the aldoses, you have the trios; you have tetrose.1824

You have a pentose; you have a hexose, 3 carbon, 4 carbon, 5 carbon, 6 carbon.1830

Of the hexoses, now, you have your D-glucose, D-mannose, you have D-allose, etc.1837

You have 8 of them, and then, you also have the L-glucose, the L-mannose, the L-allose, etc. - the other 8.1852

I hope that makes sense; what is important is number of chiral carbons.1860

Two to that number gives you how many stereo isomers there are.1865

Now, don't worry, we are actually going to draw all of these out.1869

OK, let's look at all 8 of the D-hexose stereo isomers.1873


Let's do this in black.1884

Let's get this again; there we go.1888

Let's look at...alright...let me see here.1892

Let's look at all the D-hexose stereo isomers.1902

If you have a 6 carbon sugar, of those 6 carbons, 4 of them are chiral centers.1919

That means we have a total of 16 stereo isomers.1924

Of that 16, half are D, half are L.1928

We are not going to be concerned about the L because physiologically D-sugars are what is important.1932

So, we are going to look at the 8 D-hexoses.1938

Alright, let's go.1940

1, 2, 3, 4, 5, 6, OK, this is an aldose.1944

I'm going to go ahead and put my H over there.1954

Now, OH, OH, OH, OH, H2OH, I'm going to leave the hydrogens off.1958

Notice, all the hydroxys are on the right.1969

The particular stereo isomer where all the hydroxys are on the right, this is called D-allose- that's it.1972

Repeat, 1, 2, 3, 4, 5, 6, put my aldehyde group up there; put that there.1984

Now, this one, I'm going to put on the left; but the others, I'm will leave on the right.1998

So, the first chiral carbon, this one, which is the carbon no. 2.2005

All I have done is I have switched the configuration on that one.2012

That gives me D-altrose.2015

OK, now, let's go 1, 2, 3, 4, 5, 6.2020

This time I think I'm just going to put my H on the right; I hope you don't mind.2028

Here, I put them on the left, on the right; it doesn't really matter because it is not chiral.2030

It does not really matter where it goes.2034

I'm going to frame it with my H2OH right there.2037

Now, I'm going to go back to the original2040

I'm going to leave the first chiral hydroxy to the left, and now, I'm going to move the second hydroxy to the left.2043

I'm sorry; I'm going to leave the first hydroxy on the right.2052

I'm going to take the second hydroxy, and move that one on the left, leaving everything else there.2055

This is our D-glucose.2060

That is the one we want: 6 carbons, 1, 2, 3, 4 chirals.2065

The pattern is right, left, right, right, right, left, right, right, as you go down.2073

That is D-glucose.2079

So, D-glucose happens to be the isomer of the 8 D-hexoses where the third carbon happens to have the hydroxy on the left.2081

The other carbons, the second, the fourth, and the fifth, the chiral carbons have the hydroxys on the right.2093


Now, C, C, C, C, C, C.2104

Aldehyde is here; H2OH is here.2111

Now, if I leave the first chiral and the second chiral on the right, this time, if I take the third chiral, I end up with D-glucose.2117

And again, these are all very, very different.2130

I mean, they behave the same way, but they are not the same thing- completely different molecule.2131

The configuration here is different than here.2136

OK, let's do C, C, C, C, C, C.2140

We have our aldehyde group; we have that.2156

Now, I'm going to, so here I have the first one, the second chiral, now, the third chiral.2159

Now, I'm going to go ahead and do the first 2 to the left.2169

Let me put the Hs a little bit closer, OH, but I'm going to leave this one on the right, and this one on the right.2176

This one has to stay on the right because that is the D; that is what designates the D.2185

If I were to do the L-hexoses, I would just move this hydroxide to the left because that is the reference carbon- the fifth carbon.2190

This is D-mannose.2197

Now, let's do this one, C, C, C, C, C, C, H2OH; we have our aldehyde.2203

Now, I'll do that one, and that one.2214

I'll leave that one on the right, and that one.2222

This is called D-idose.2225

OK, we are almost there.2229

Let's go, 1, 2, 3, 4, 5, 6, CH2OH; we draw our aldehyde.2236

Now, we will leave the first chiral on the right.2248

This time we will take the second and the third, and then, we will leave this one on the right.2251

This one is going to be D-galactose- also a very important sugar that tends to come up a lot.2256

And, of course, our last one, C, C, C, C, C, C, H2OH.2265

As you can see, by the time you've actually gone through these 8, you should have a pretty good command of drawing these structures; that is that one.2274

Now, we are going to have all 3 on the left.2283

That one, no, this is not going to work.2290

I need the hydroxys a little bit closer.2296

OH, OH, OH, and, of course, this one stays on the right because that is what designates it.2299

That is a reference carbon that designates it.2306

D...this is talose.2308

There you go.2314

Those are the 8 stereo isomers of hexose- that's it.2315

One of those happens to be glucose.2326

The one that has the pattern, right, left, right, right, for the hydroxys that are attached to the non-carbonyl carbon.2329

That is going to be the important sugar.2338

OK, now, some things to notice; put this in red.2341

Very, very important to notice this.2349

The no. 5 C, the no. 5 carbon, does not change configuration.2354

That one does not change configuration.2365

It is the reference carbon, and it makes these hexoses D-hexoses.2376

If I drew the hydroxy on the left, then, it would be an L-hexose.2395

It might have the same thing, except now, this one is on the left; I’d have another 8.2399

Now, let's go ahead and define something called an epimer or epimer; some people say epimer.2407

Again pronunciation, completely irrelevant.2413

Despite what some people might tell you, it is not relevant.2417

2 monosacchs that differ, if you have 2 monosaccharides that differ in the configuration around 1 carbon, those are called epimers.2421

2 monosacchs that differ in the configuration around one carbon, those are called epimers.2450

Let me give you an example of that.2456

OK, I'm going to draw glucose in the center.2460

So, let's go 1, 2, 3, 4, 5, 6, CH2OH2463

I have my aldehyde; I have my right, left, right, right patterns.2472

So, this is my D-glucose, my primary central monosaccharide.2480

Now, over here, let me go ahead and draw C, C, C, C, C, C, 1, 2, 3, 4, 5, 6, yes.2487

This is CH2OH; this is my aldehyde, and what did I use?2497

I did, oh, I did mannose.2502

OK, this is going to be left, left, right, right.2505

Notice, the only thing that I've changed is that one.2515

This one is left, left, right, right, right, right; everything is the same.2521

The only difference is, at the no. 2 carbon, these differ in configuration.2525

Here, hydroxy is on the right; here hydroxy on the left.2535

This is D-mannose, and it is called a C2-epimer of glucose, or you could say that glucose is a C2-epimer of D-mannose, or you can just say that they are C2 epimers- relative.2538

So, the only carbon that's different is the 2 carbon.2560

Now let’s do another one.2564

Let’s go 1, 2, 3, 4, 5, 6, we have that; we have that.2567

Now, what did I do?2576

I left that one over here; I think I left that one over there.2578

Oh, I changed that one and that one.2583

Now, let me go to black.2588

Now, the only difference is, this one and this, those are the same; this one and this, those are the same.2591

Ah, I changed that one on the 1, 2, 3, on the 4th carbon.2598

On glucose the hydroxy is on the right; on... is this galactose?2605

Yes, that's galactose; yes.2609

On the galactose the hydroxy is on the...this is a no. 4 carbon, so this is a C4-epimer of glucose- that's it.2613

When we talk about epimers, we just mean that, on one of those carbons, usually they will specify which carbon the configuration is reversed, is different- that's it.2627

Now, notice, this does not change the DL.2638

The DL is based on this carbon, the reference carbon.2642

Notice, hydroxy is on the right, D; hydroxy is on the right, D.2647

Hydroxy is on the right, D.2650

It is the one, the carbon that we matched against the configuration of glyceraldehyde to decide whether it is D or L.2655

OK, you are never going to find a 1, 2, 3, 4, 5, you are never going to have a C5-epimer- you're not.2660

I suppose you can talk about it, but we will never talk about a C5-epimer.2670


Now, let's go ahead and get to the, well, get to further elucidation of a monosaccharide structure here.2678

Let’s go ahead and go back to blue.2689

Now, oops, actually you know what, that's fine; I'll go ahead and leave it as black.2693

Now, in aqueous solution, so these monosaccharides, they are very, very soluble.2702

All these hydroxy groups, lot of hydrogen bonding, they are almost infinitely soluble.2709

I mean, you can dissolve a whole bunch, you know that already; you can dissolve a whole bunch of sugar in water, in a very little amount of water.2713

In aqueous solution, in other words, our bodies, aqueous solution, the monosacchs with greater than or equal to 4 carbons, they tend to exist in their ring formations.2720

In other words, if you were to take like D-glucose as a straight chain sugar like this, and if you were to drop this in water, one of the hydroxys and this carbonyl would actually react with each other in an intramolecular reaction; and it will for a ring.2755

In aqueous solution, most of these monosaccharides, they exist predominantly in their ring formation; and we are going to actually talk about, we are going to draw out how the ring forms in just a minute.2775

So, in aqueous solution, monosacchs with greater than or equal to 4 carbons tend to exist in their ring formations.2786

What that means is that 1 of the OH groups on the monosacch has reacted with the carbonyl carbon, has reacted with the carbonyl group, to form a hemiacetal or a hemiketal.2793


Now, some of you may be coming to this biochemistry course having taken only 1 term of organic chemistry; and my guess is that that particular term definitely discussed alcohols, but you may not yet have seen carbonyl chemistry.2846

The chemistry surrounding the carbon oxygen double bond, probably the most important chemistry of organic chemistry, and certainly of biochemistry, the most important functional group.2862

When an alcohol, the hydroxy group reacts with the carbonyl, it form something called a hemiacetal or hemiketal,2874

We will do the chemistry in just a minute.2884

It is not the name that I want you to know.2890

I mean, yes, it is nice to know that it is a hemiacetal or a hemiketal.2892

In other words, when one of the aldehyde, one of the aldoses reacts, you are going to get a hemiacetal.2896

When one of the ketoses reacts, you get a hemiketal.2901

It is the chemistry that I want you to understand.2905

That is what's important.2909

Let's just go ahead and make sure that that is well-understood.2910

The name itself, you might see it occasionally here and there, but it is the chemistry that's important.2915

OK, now, here is the important part.2920


In the process of reacting, the carbonyl carbon is converted to a chiral carbon.2928

So, the carbonyl carbon is not chiral.2953

The double bond, there is no chirality there; but when it reacts, the double bond breaks and now becomes a single bond.2955

Now, you have 4 different objects attached to that carbonyl carbon.2961

In the process of reacting, forming the hemiacetal or hemiketal, the carbonyl carbon is converted to a chiral carbon, because the COO becomes a COH.2969

It becomes an alcohol.2994

Now, it has 2 configurations available to it.3002

Now, that it is chiral, it also has 2 configurations, 2 enantiomers at that carbon, 2 configurations available.3016

We call them alpha and beta.3030


Now, I'll actually go ahead and leave it that way.3037

So, once it reacts, that carbonyl carbon is converted to a chiral carbon.3042

That chiral center has 2 configurations.3047

One of them, we call alpha; one of them, we call beta.3050

Now, let's go ahead and follow this very, very carefully.3052

Let's follow the formation of the 2, actually you know, I'll make sure to write everything out; I mean, I know we know what is going to happen, but OK.3056

Let's follow the ring formation of the alpha and beta configurations of D-glucose.3086

OK, let's go ahead and draw out D-glucose.3106

This is going to be...do this in blue.3110

I have got 1, 2, 3, 4, 5, 6, 2, 3, 4, 5, 6, yes, I have CH2OH.3112

I have my aldehyde group, and, of course, I have right, left, right, right.3123

OK, here is what I'm going to do, and here is how I think about it.3132

When we do the final structures, you can actually arrange it; and you can think about it anyway you want to, but here is how I think about it.3137

I take this vertical arrangement of the glucose, and what I do is rotate it 90 degrees to the right.3144

In other words, I take this molecule, and I just rotate it 90 degrees to the right; then what I do is, I've got the aldehyde on the right.3150

I have got this on the left, then I take this side of the molecule, and I go around to my left from the back, and I attack the carbonyl from the back on the right-hand side; and now, I'll show you what that looks like.3158

Let me go ahead and draw this as...actually, you know what, I'm probably going to need a little room here.3175

I'm going to go COH, and I'm going to go ahead and put the electrons there.3184

C, C, C, C, there is my carbonyl, and I'm going to go ahead and put my H down here.3190

Here, I have got OH; this is right, left.3206

That is there; this is going to be CH2OH.3218

OK, see what I've done.3225

I've rotated this to the right; I've put this carbonyl over on the right.3227

Now, I have taken this group, and I've brought it around to the back.3231

So, this part is the front; from here back, this is actually going back behind the page.3235

I have the aldehyde part, and I take this hydroxy, and I loop it around the back.3242

My carbonyl is here from your perspective.3250

The carbonyl is here, I take this OH group as on the left, and I loop it around behind, so that the hydroxy group is actually coming from behind this way because I want this oxygen on the back and on the right from your perspective.3254

OK, and here is what happens.3268

Well, these electrons, this is nucleophilic hydroxide, right?3270

These electrons, this is an electrophilic.3275

This is going to attack there, and it is going to cause those electrons to move; and it is going to go ahead and grab an H+ from solution, and turn this into a hydroxy.3279

I'm actually going to show that.3289

You know what, I'm going to do this in a different color; sorry.3293

Let me go ahead and put the electrons here.3298

Let me go ahead and do the mechanism in black.3300

These attack the carbonyl, and it goes ahead and it grabs this.3304

Now, here is what happens.3310

You are going to get 2 different structures here.3314

Now, the carbonyl carbon, this is flat.3317

If I have the C and that, this is flat; the carbonyl is flat.3322

This is the carbon, this is the double-bonded oxygen.3331

This hydroxy, you remember, the carbonyl can be attacked from 2 sides, OK.3335

It isn’t attacked that way; it's attacked from the top and from the bottom.3339

If it is attacked from the top, it is going to push the oxygen down.3343

If it is attacked from the bottom, it is going to push the oxygen up, because now, this double bond is turning into a single bond; and it is going to assume a tetrahedral arrangement.3347

It is true that we took it, and we are attacking it from this side; but what is happening is, we are actually attacking it from the top, or we are attacking it from the bottom.3362

That is what's going on.3371

So, you get 2 possible things going on.3373

This one, we will say, this is an attack from above, and this is attack from below.3377

There is attack this way, or there is attack this way.3388


Now, let's go ahead and draw the structures that we end up getting.3394

You end up with the following.3398

I'm going to draw these in black actually, and I'm going to write out all of my carbons because I love drawing out everything.3401

C, C, C, C, O, OH, H, this goes down.3409

This one is up; this one is down, and this is CH2OH.3421

Did I forget anything here?3428


This is called the alpha-D-glucose; this is D-glucose, OK.3433

The D-glucose part is the configuration of the hydroxys.3436

The alpha part means that it is attacked from above.3442

Now, this hydroxy here is down.3445

If I'm looking at the ring this way.3450

Imagine this is flat; I'm looking at it like that.3454

If the hydroxy is below the ring, that is the alpha-D-glucose.3459

That means it was attacked from above, so it pushed that oxygen down.3462

This right here, that is the carbonyl carbon.3466

OK, this was originally the carbonyl carbon; that one right there.3471

OK, now, that is alpha-D-glucose.3474

If I have attacked from below, so that the hydroxide ends up above the ring, it is going to look like this: C, O, C, C, C, C.3480

I'll make it a little bit more uniform here.3491

C, C, C, this time, when the tetrahedral arrangement is such that this hyrdoxy is above the ring.3494

And again, notice, everything stays the same.3502

That one is down; that one is up.3504

That one is down, and this one doesn't matter.3508

This is beta-D-glucose.3512

The hydroxy is above the ring.3517

OK, hydroxy is up here.3521

Here, the hydroxy is below- that is alpha-D-glucose.3524


Now, here we go.3532

The carbonyl carbon, the carbonyl C, which is this one, which is now a hemiacetal, and all that means is that this was a carbonyl carbon.3537

Now, it has a hydroxy group attached to it, and it also has an oxygen connected to a carbon group.3557

OK, there is an ether function, COC, and there is an alcohol function.3566

Both oxygens are attached to this carbon.3576

That is the carbonyl carbon.3580

We draw it like this, specifically.3582

We put the carbonyl carbon on the right; we put the oxygen on the back right, and we arrange it like this, but I'll talk more about that in just a second.3583

So, the carbonyl carbon, which is now a hemiacetal - and again, hemiacetal means hydroxy group, ether group, hydroxy group, ether group attached to that - is called the anomeric carbon, and the 2 isomers namely alpha and beta.3591

It is called the anomeric carbon.3602

And, the 2 isomers namely alpha and beta, OK.3617

OK. This is the only place that the configuration is different; everything else is the same.3625

OK, down up down, down up down, nothing, nothing, up here, down here.3631

It is the only place, OK.3637

The isomers, and the 2 isomers of the anomeric C are called, well, you guessed it- anomers.3640

Alpha-D-glucose and beta-D-glucose are anomers of each other because the configuration is different only at the anomeric carbon.3657

The anomeric carbon was originally the carbonyl carbon, the aldehyde.3669

There was an intramolecular reaction.3673

So, 1, 2, 3, 4, 5, there was an intramolecular reaction of this hydroxy group attached to the no. 5 carbon that reacted with the carbonyl to form this hemiacetal.3679

Hemiacetal is a hydroxy group attached to that carbon, an ether group attached to that carbon.3691

That is what's going on here.3697


Now, let's go ahead and follow the same thing for fructose.3702

Yes, this one I'll do in blue.3707

I want you to see it again, that's why I'm going to go through it.3709

Let's follow the ring formation for fructose.3712

And again, fructose is a ketose.3726

Let's go ahead and draw it out.3729

Again, we have 6 carbons; we have 1, 2, 3, 4, 5, 6, but this time, we have the carbonyl here.3733

We have the H2OH here; we have the H2OH here.3746

This is there; this is there, and this is there.3752

Again, it is going to be the hydroxy on the no. 5 carbon, 1, 2, 3, 4, 5; let me number them- 1, 2, 3, 4, 5.3758

It is going to attack the carbonyl, but notice, now, we have 1, 2, 3, 4, 5 members in the ring, not 6 members in the ring because now, the carbonyl is not on this carbon, it is over here.3774

Let me go ahead and turn this around so you can see it.3789

Again, rotate it to the right.3790

Rotate the molecules to the right; take this side, and bring it around the back.3794

That is what we want to do; we always want the anomeric carbon to be over here.3800

OK, when I do that, I'm going to end up with the following.3807

Let's go, should I do this in blue?3812

Yes, let's do this in blue.3815

I have got C, C, C, C, and I've got OH, 1, 2, 3, 4; oh, yes, of course, sorry about that.3817

I have got this one over here, CH2OH, and this is my carbonyl; there we go.3838

I got lost for a second there.3843

OK, this one is up; this one is down, and this one is there.3845

Now, again, we have attacked from above, attacked from below.3855

Yes, that is fine.3861

Let me go ahead and draw the mechanism.3863

Let me put an H+ out there; this attacks the carbonyl.3867

This goes ahead and grabs that, and again, we have 2 possibilities.3871

This is attack from above.3879

OK, this is attack from below, and you end up with the following.3889

This time, for the 5-membered rings, we put the oxygen on the top; and we go C, C, C, C, C.3896

And now, if we do attack from above, that is going to push this oxygen down.3909

So, you end up with the hydroxy down here.3916

You end up with CH2OH there.3920

You end up with CH2OH here, and here, we have the OH up; and this is the OH down, and this is alpha-D-fructose, alpha, because the hydroxy is below the ring.3924

Attack from above...wait...that's from above.3944

From below, we are going to push the oxygen up.3948

We are going to end up with the following.3951

Let's go back to black here; put our oxygen there, carbon, carbon.3953

Let me number my carbons, by the way.3960

This is 1, 2, 3, 4, 5, so the hydroxy on the no. 5 carbon again.3963


This time from below, we are going to push the hydroxy up.3975

Let me go ahead and draw my ring first; let me close that one out.3979

This one is going to be CH2OH; this is going to be CH2OH.3982

This is going to be OH here; this is going to be OH there.3990

This is beta-D-fructose.3994

Again, arrange it horizontally, come around.4001

This is 1, 2, 3, 4, 5; the hydroxy attacks the no. 2 carbon.4006

In this particular case, this is your anomeric carbon.4015

Again, it is on your right-hand side.4018

Oxygen is on the top here, top here.4020

It gives you the beta-D-fructose, beta, because the hydroxy is above the ring.4024

When you look at this, you are looking at it like this, but really what you are looking at is - I've drawn it this way oxygen, carbon, carbon, carbon - you are looking at it that way.4029

And, we will actually do a prospective drawing in just a moment called a Haworth projection, but you are looking at it that way.4039

That is what's happening.4044

You have the hydroxy either up here or the hydroxy down here.4046

Hydroxy down here is alpha; hydroxy up here is beta.4048

OK, now, let's finish this up here.4053

So, we have got 6-membered rings.4059

6-membered rings are called...and again, you know, well, let me write down the name- pyranose.4067

One of the most frustrating things about biochemistry for me, personally, has always been the vocabulary.4080

You have got aldose; you've got hexose.4086

You have got pyranose, so 6-membered rings are called pyranose.4089

See, you have got all of these names for the same thing.4092

And again, in any conversation that you'll have with a professor or a student or something like that, anyone of those people is going to use anyone of those terms.4095

So, it is a little annoying to have to have all these terms floating around.4106

It gives the impression that you are talking about a whole bunch of different things- you are not.4110

You are talking about 1 molecule.4114

It is just, all these names that are attached to it depending on what we want to emphasize, and a lot of this is just historical garbage in the sense that this stuff has just, sort of, stayed, and we have used it, and we have used it; and now, we have this build-up of all these stuff from the history of biochemistry that we now have to synthesize, that we now have to bear on our shoulders.4118

All I can say about that is "I'm sorry"'; it is just as annoying to me as it is to anybody else.4137

I never use the word pyranose, but there it is.4142

OK, 5-membered rings, and I'll tell you in a minute why they are called pyranose and furanose.4147

5-membered rings are called furanose, and I can never remember which is which.4157

Is pyranose 6; is furanose 6?4165

Anyway, OK, now, let's talk about something called a Haworth projection.4168

Let's go ahead and do this in black.4178

Haworth projection- this is a way of looking at these sugars in 3-dimensional way.4183

We will do a Haworth projection of the pyranoses, and these are 6 carbons, yes.4192

I'm going to draw the projections, the I will draw the bases of the name pyranose.4201

OK, here is what you've got.4206

This time, I'm not going to draw out all of the individual Cs.4208

I'm going to do it in a line structure.4212

This is going to be O, boom, boom, boom, boom.4215

I want a little bit better than that.4225

OK, let's go ahead and do the alpha, OH, OH, OH, CH2OH.4241

OK, this is alpha-D-glucose.4254

Yes, it is fine; I'll just go ahead and write it- alpha-D-glucose.4261

Notice this particular projection, how we have done it.4266

Remember we said the sugar, so now, it's a ring.4268

You have go this 1, 2, 3, 4, 5, 6; the oxygen is on that side.4270

You are looking at it that way; that is what you are doing.4274

That is what this projection is.4277

The single lines, the normal lines, those are in the back; these bold lines, it comes out as a wedge, and then it stays bold like that.4280

Those are coming out towards you, and what it does is it gives you a way of seeing what is above the ring and what is below the ring.4287

Now, you remember that anytime you have a 6-membered ring, you don't have a flat ring.4294

What you have is a chair and boat confirmation.4299

Won't talk about that right now, I will in the next lesson, a little bit; but this is a really, really great projection because it shows you what is above and what is below the ring.4302

In this particular case, you have the hydroxy below the ring, so you have the alpha-isomers.4310

This is alpha-D-glucose, and notice how this is arranged.4318

The oxygen is on the top right, and the anomeric carbon is on the right.4321

This is why we said, take your molecule, rotate it to the right, make sure the anomeric carbon is right there.4327

The carbonyl, bring this side around the back, and your oxygen will actually end up staying back there.4333

That is the way you want to think about it.4338

Rotate to the right; bring it from the back, and attack above or below to create the ring.4339

OK, this is alpha-D-glucose.4346

Now, let me go ahead and do beta-D-glucose.4347

Again, we have our oxygen, we that, that, that, that.4352

I'm telling you, I don't think they will ever improve drawing these things year after year. 4367 OK, that is that, there, there, there, there.4361

Again, we've got, comes out as a wedge, bold, something like this.4374

Now, we have our beta with a hydroxy above there, and this stays.4382

This is down; this is up.4386

This is down, and this is like that.4390

This is the beta-D-glucose.4393

OK, now, some things, blue.4399

I love jumping around with these colors; it's really, really great.4407

OK, oxygen is at the back right always.4411

OK, the anomeric carbon is on the right.4425

Anomeric carbon, oxygen, anomeric on the right, oxygen, back right.4440

If you want, you can put the electrons on the oxygen, it doesn't really matter.4444

Now, here is why we call it a pyranose.4447

Yes, that is fine; I'll go ahead and do it in black.4457

Well, basically what you have is this.4463

This molecule is called pyran, and if I were to draw it in perspective, it would look like this.4470

OK, this is pyran.4479

It is based on this thing with the hydroxys attached, so they call it a pyranose- that is why.4481

That is where the name comes from.4487

I never cared for it very much, in fact I rather dislike it, but there it is.4490

OK, now, let's do our Haworth projections for the furanoses 5, yes.4496

OK, let's go back to blue, and this time we put the oxygen on the back, but the anomeric carbon is still on the right.4520

Again, we have...you know what, let me start again.4530

OK, we have got O, boom, boom, boom, boom, boom.4538

So, we have got, this comes out into a wedge, and this is a bold line here; and this comes out to a wedge, or you can just make them all bold.4545

It doesn't really matter all that much.4554

We have got an OH here; we have got CH2OH here.4557

In this particular case, that is up; that is down.4563

This is CH2OH; this is the hydroxys down below the ring, right?4570

This is this way; oxygen is back here.4574

1, 2, 3, 4, 5, we are looking at it like this.4577

The hydroxy is down below.4582

This is alpha-D-fructose.4585

I think I have got everything there, I hope, yes.4590

And, now, let's go ahead and do beta, boom, boom, boom, boom, boom.4594

And then let's go ahead and bold this out, bold this out, bold this out.4603

And now, we have the hydroxy on top, the CH2OH below.4609

This CH2OH stays.4614

This hydroxy is up; this hyrdoxy is down.4618

Is that correct?4622

Yes, that is correct.4625

So, this is beta-D-fructose.4627

A lot of structures we're drawing.4632

And, they are called furanoses because of this molecule.4634

This particular molecule is called furan.4641

They consider it a derivative of some sort, just a whole bunch of hydroxys attached to it.4649

So, that is it; that is our introduction to monosaccharides.4654

Thank you so much for joining us here at Educator.com4660

We'll see you next time for a further discussion of carbohydrates.4662

Take care, bye-bye.4665