Chapter 11. Carbohydrates

• Monosaccharides• Oligosaccharides• Polysaccharides• Glycoproteins

Carbohydrates

• Gluconeogenesis and photosynthesis• Oxidation of carbohydrates provides

energy to sustain life• Energy storage — starch or glycogen• Structural function – cellulose, chitin

peptidoglycan & glycosaminoglycans• Glycoconjugates - glycoproteins &

glycolipids

• Chemical nature of carbonyl group– Aldose : carbonyl is an aldehyde– Ketose : carbonyl is a ketone

• Number of carbon atoms– Trioses (C3)– Tetroses (C4)– Pentoses (C5)– Hexoses (C6)– Heptoses (C7)– etc

Classification of monosaccharides

D-Aldoses

D-Ketoses

ketotetrose

ketotriose

ketopentoses

ketohexoses

EpimersSugars that differ only by the configuration around one carbon atom

Hemiacetals and hemiketals

Cyclization of monosaccharides

Cyclic sugars have two anomeric forms

β-anomerα-anomer

Sugars are conformationally variable

Two chair conformations of β-D-glucopyranose

Sugar derivatives

• Aldonic acids – oxidation of an aldehydegroup in an aldose to an carboxylic acid

• Uronic acids – oxidation of a primary alcohol group to an carboxylic acid

• Alditols – reduction of aldoses and ketoses• Deoxy sugars – replacement of OH with H• Amino sugars – replacement of OH with

NH2• Sugar phosphates

Aldonic acids and uronic acids

D-Glucuronic acidD-Glucose D-Gluconic acid

Alditols

Deoxy sugars

Amino sugars

Sialic acids(NAM)

Sugar phosphates

O-Glycosides

N-Glycosides

French Fries à la Plastic

Neurotoxin and suspected carcinogen !!!

Disaccharides

Artificial sweeteners

SucraloseAspartameSaccharin

Polysaccharides (Glycans)

Polymers of monosaccharides linked together by glycosidic bonds

• Homo or heteropolysaccharides• Linear or branched polysaccharides

Storage polysaccharides

• Starch – Plant• Glycogen – Animal

Starch granule in plant cell chloroplasts Glycogen granule in liver cells

Starch

Helical structure of amylose

Glycogen

Structure of amylopectin or glycogen

Structural polysaccharides• Cellulose

– Plant cell walls– Marine invertebrates (Tunicates)

• Chitin– Exoskeletons of invertebrates (Crustaceans, Insects,

Spiders)– Cell walls of most fungi and many algae

• Glycosaminoglycan (=Mucopolysaccharides)– Connective tissues (Cartilage and tendons) or

extracellular matrix (ground substance) of higher animals

Cellulose

n

Glucose Glucose

Chitin

Glycosaminoglycans (Mucopolysaccharides)

n n

n n

n n

Glycosaminoglycans• Hyaluronic acid – connective tissue, synovial

fluids, vitreous humor of the eye• Chondroitin sulfate – cartilage and other

connective tissue• Dermatan sulfate – skin • Keratan sulfate • Heparin – component of intracellular granules of

the mast cells (blood-clotting inhibitor)• Heparan sulfate – cell surface and extracellular

substance in blood vessel and brain (interaction with fibroblast growth factors and their receptors)

Glycoproteins

• Proteoglycans• Peptidoglycans• Glycosylated proteins

Proteoglycans

Bacterial cell walls

Peptidoglycans

Antibiotics targeting peptidoglycans

Glycosylated proteins

• Proteins often contain oligo or polysaccharides

• Sugar modification are mostly seen in extracellular or transmembrane proteins

• Protein can contain 10-90% carbohydrates• Carbohydrates are usually linked through

asparagine (N-linked), or serine or threonine (O-linked)

O- and N-linked oligosaccharides

Oligosaccharide dynamics

Turnover of serum proteins

Cell surface

Lectins

Proteins that specifically recognize carbohydrate

ABO blood types