Chapter 11:Carbohydrates

Copyright © 2007 by W. H. Freeman and Company

Berg • Tymoczko • Stryer

BiochemistrySixth Edition

Carbohydrates

Common termsMonosaccharides: glucose, fructose, mannose, etc.Disaccharides: maltose, cellibiose, sucrose, lactosePolysaccharides: starch, glycogen, chitin,

glycosaminoglycansAldoses, ketoses Pentoses, hexosesPyranose, furanoseAnomeric carbon atom, anomers, D,L isomers, epimers, penultimate carbonGlycosidic bond, hemiacetal, acetalMutarotation Reducing sugar

Trioses (three carbons)

aldose aldose ketose

* Know

**

Aldose familyAdlose family

* Know

*

*

* * *

Ketose familyKetose family *

*

*

* Know

D-Stereochemistry of Glucose

Convention for the Fischer projection:

Carbonyl (#1C) is at the top.

OH to right = "D"OH to left = "L"

CHO

H C OH

H C OH

H C OH

HO C H

CH2 -OH

Penultimate C

Glucose is assigned the D stereochemistry because the penultimate carbon atom is D.

Hemiacetal formation

Pyranose and Furanose forms

Hemiacetal, Haworthstructure

Hemiketal,Haworthstructure

Haworth Structure of Glucose

-anomer

-anomer

Draw Fischer, rotate 90o, then form the hemiacetal

Haworth Structure of Fructose

Ribose and DeoxyribseHaworth structures

Mutarotation of Fructose

Openchainform

Mutarotation of Glucose

Open chain Form~0.003%

-D-glucopyranose 36%, D = 112o

-D-glucofuranose~0.5%

-D-glucopyranose 63%, D = 18.7o

-D-glucofuranose~0.5%

Observed rotation = 52.7o

Glycosidic bond (acetal)

Three glucose residues

The connections (gycosidic bonds) are ( 1-4)

Lobry de Bruyn-Alberda von Eckenstein rearrangement

HO C H

H C OH

H C OH

CH2-OH

C O

CH2-OH

HC=O

H C OH

H C OH

H C OH

HO C H

CH2 -OH

CHO

H C OH

H C OH

CH2 -OH

HO C H

HO C H

CH-OH

H C OH

H C OH

CH2 -OH

C OH

HO C H

H-O-

enediol

glucose mannose

fructose

Reactionof a sugarin NaOH.

Methylation of Glucose

Converting a hemiacetal to an acetal.

HO-CH2

OHHO

O

OH

OH

CH3OH

HO-CH2

OHHO

O

H+

OH

OCH3

Glycosidic bond (an acetal)

Methylation of Glucose

Exhaustive methylation forms one glycocidic bond and the rest are ethers.

CH3I

HO-CH2

OHHO

O

OH

OH

CH3O-CH2

OOCH3

CH3O

OCH3

OCH3

HOH

H+

CH3O-CH2

OOH

CH3O

OCH3

OCH3

excess

Sugar Derivatives

Also, oxidized or reduced or phosphorylated or amino sugars

Sugar Oxidation at C-1

Gluconic acid

Sugar Oxidation at C-6

Sugar Phosphates

N-Acetylmuramic acid

N-acetylglucosamine + lactate, A component of bacterial cell wall.

NH-C-CH3

HO-CH2

OOHHO

CH3-CH-COOH

O

O

N-Acetylneuraminic acidN-acetylmannosamine + PEP

C-CH3

HO-CH2

OH CHO

HO

OH

O

NHC-CH3

HO-CH2

OHHO

O

O

NHOH

COO-HOH

CH2

C-O-PO3=

..

C-CH3

HO-CH2

OH CH

HO

OH

O

NH

COO-

H-O

CH2

C-O-PO3=

..

OH

C-CH3

HO-CH2

OH CH

HO

OH

O

NH

COO-

CH2

C=O

OH

CH3-CCHOH

OH

O

O

NH

OH

COO-

CH2OH

CHOH

Pi

Common disaccharides

1. Maltose: -D-glucopyranosyl-(14)--D-glucopyranose

2. Cellibiose: -D-glucopyranosyl-(14)--D-glucopyranose

3. Lactose: -D-galactopyranosyl-(14)--D-glucopyranose

4. Sucrose: -D-glucopyranosyl-(12)--D-fructofuranoside

The anomeric OH in 1, 2, & 3 may be or but sucrose may not.

Maltose, a disaccharide

Other disaccharides

Cellibiose

Common Homopolysaccharides

1. Amylose (linear starch)An-(14)-D-glucose polymer

2. Cellulose (linear)A -(14)-D-glucose polymer

3. Amylopectin (branched starch)An -(14)-D-glucose polymer branched -(16)

4. Glycogen (branched)An -(14)-D-glucose polymer branched -(16)

5. Chitin (linear)An -(14)-D-N-acetylglucosamine polymer

GlucopolysaccharidesHomopolysaccharides

A 1-6 branch point

This branch occurs in glycogen and amylopectin. However, glycogen is more highly branched.

A high energy glucose carrier

Heteropolysaccharides Glycosaminoglycans(disaccharide repeating units)

Chondroitin-6-sulfate:-D-glucuronic acid-( 13)-N-acetyl-D-galactosamine-6-sulfate-( 14)-

Keratan sulfate:-D-galactose-( 14)--acetyl-D-glucosamine-6-sulfate-( 13)-

Heteropolysaccharides Glycosaminoglycans(disaccharide repeating units)

Dermatan sulfate:-L-iduronic acid-( 13)-N-acetyl-D-galactosamine-4-sulfate-( 14)-

Hyaluronic acid:-D-glucuronic acid-( 13)-N-acetyl-D-glucosamine-( 14)-

A Proteoglycan

A glycoconjugate:(polysaccharide linked to a protein or peptide)

ProteogycanElectronmicrograph

Complex Carbohydrates

L-Fucose

L-fucose is 6-deoxy-L-galactose

CHO

HO C H

H C OH

HO C H

H C OH

CH3

Linkages in Glycoproteins

N-Linked Carbohydrate

High mannose

N-Linked Carbohydrate

Complex carbohydrate

Dolichol phosphate (isoprenoid)

This is the endoplasmic reticulum membrane anchor on which the core carbohydrate for a glycoprotein is synthesized. It is then modified in a Golgi body.

From Golgi to Lysosome

Mannose-6-P is a marker that directs some hydrolytic proteins from a Golgi body to a lysosome where glycolipids and glycosaminoglycans are degraded.

Hydrolysis of theN-acetylglucosamine to leave a Mannose-6-P residue.

Review - Glycoconjugates

1. Proteoglycans (glycosaminoglycans + protein).Mostly carbohydrate (~85%), e.g. cartilage

2. Glycoproteins (most 1-10% carbohydrate). N and O linked complex carbohydratese.g. receptors

3. Peptidoglycans (carbohydrate + small peptide). e.g. bacterial cell wall

Proteoglycan

Sketch

PeptidoglycanBacterial cell wall (murein): A long linear

polymer of:

-N-acetyl-D-glucosamine-( 14) -N-acetyl-Muramic acid-( 14)-

A tetrapeptide is attached through the carboxyl of the lactate moiety of muramic acid.

Lactate-CO-L-Ala-D-isoGlu-L-Lys-D-Ala-

Peptidoglycan

Bacterial cell wall:

Lactate-CO-L-Ala-D-isoGlu-L-Lys-D-Ala-

In gram (+) bacteria crosslinks are formed by a pentaglycine bridge from the D-Ala residue above to the L-Lys in another peptide. (Outer surface is carbohydrate)

In gram (-) bacteria crosslinks are formed by a direct link from the D-Ala residue above to the L-Lys in another peptide. (Outer surface is cell membrane)

Gram Positive (+) Cell Wall

Up to 20 layers of peptideglycan

Gram Negative (-) Cell Wall

Monolayer of peptideglycan

End of Chapter 11

Copyright © 2007 by W. H. Freeman and Company

Berg • Tymoczko • Stryer

BiochemistrySixth Edition