Biochemistry Sixth Edition Berg • Tymoczko • Stryer Chapter 11: Carbohydrates Copyright © 2007 by W. H. Freeman and Company

Carbohydrates Common terms Monosaccharides: glucose, fructose, mannose, etc. Disaccharides: maltose, cellibiose, sucrose, lactose Polysaccharides: starch, glycogen, chitin, glycosaminoglycans Aldoses, ketoses Pentoses, hexoses Pyranose, furanose Anomeric carbon atom, anomers, a, b D,L isomers, epimers, penultimate carbon Glycosidic bond, hemiacetal, acetal Mutarotation Reducing sugar

Trioses (three carbons) * Know * * aldose aldose ketose

* Adlose family Aldose family * Know * * * *

* Ketose family Ketose 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" Glucose is assigned the D stereochemistry because the penultimate carbon atom is D.

Hemiacetal formation

Pyranose and Furanose forms Hemiacetal, Haworth structure Hemiketal, Haworth structure

Haworth Structure of Glucose Draw Fischer, rotate 90o, then form the hemiacetal a-anomer b-anomer

Haworth Structure of Fructose

Ribose and Deoxyribse Haworth structures

Mutarotation of Fructose Open chain form

Mutarotation of Glucose b-D-glucofuranose ~0.5% a-D-glucofuranose ~0.5% Open chain Form ~0.003% a-D-glucopyranose 36%, aD = 112o b-D-glucopyranose 63%, aD = 18.7o Observed rotation = 52.7o

Glycosidic bond (acetal)

Three glucose residues The connections (gycosidic bonds) are (a 1-4)

Lobry de Bruyn-Alberda von Eckenstein rearrangement Reaction of a sugar in NaOH.

Methylation of Glucose Converting a hemiacetal to an acetal.

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

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.

N-Acetylneuraminic acid N-acetylmannosamine + PEP

Common disaccharides The anomeric OH in 1, 2, & 3 may be a or b, but sucrose may not. Maltose: a-D-glucopyranosyl-(14)-a-D-glucopyranose 2. Cellibiose: b-D-glucopyranosyl-(14)-a-D-glucopyranose Lactose: b-D-galactopyranosyl-(14)-a-D-glucopyranose 4. Sucrose: a-D-glucopyranosyl-(12)-b-D-fructofuranoside

Maltose, a disaccharide

Other disaccharides Cellibiose

Common Homopolysaccharides Amylose (linear starch) An a-(14)-D-glucose polymer 2. Cellulose (linear) A b-(14)-D-glucose polymer Amylopectin (branched starch) An a-(14)-D-glucose polymer branched a-(16) Glycogen (branched) Chitin (linear) An b-(14)-D-N-acetylglucosamine polymer

Glucopolysaccharides Homopolysaccharides

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-(b 13)-N-acetyl-D-galactosamine-6-sulfate-(b 14)- Keratan sulfate: -D-galactose-(b 14)-N-acetyl-D-glucosamine-6-sulfate-(b 13)-

Heteropolysaccharides Glycosaminoglycans (disaccharide repeating units) Dermatan sulfate: -L-iduronic acid-(b 13)-N-acetyl-D-galactosamine-4-sulfate-(b 14)- Hyaluronic acid: -D-glucuronic acid-(b 13)-N-acetyl-D-glucosamine-(b 14)-

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

Proteogycan Electron micrograph

Complex Carbohydrates

L-Fucose L-fucose is 6-deoxy-L-galactose

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 the N-acetylglucosamine to leave a Mannose-6-P residue.

Review - Glycoconjugates Proteoglycans (glycosaminoglycans + protein). Mostly carbohydrate (~85%), e.g. cartilage Glycoproteins (most 1-10% carbohydrate). N and O linked complex carbohydrates e.g. receptors Peptidoglycans (carbohydrate + small peptide). e.g. bacterial cell wall

Proteoglycan Sketch

Peptidoglycan Bacterial cell wall (murein): A long linear polymer of: -N-acetyl-D-glucosamine-(b 14) -N-acetyl- Muramic acid-(b 14)- 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

Biochemistry Sixth Edition Berg • Tymoczko • Stryer End of Chapter 11 Copyright © 2007 by W. H. Freeman and Company