Carbohydrates & glycoproteins

relationship between D-glucose and D-galactose

galactose is C-4 epimer of glucose

relationship between D-glucose and D-mannose

Mannose is C-2 epimer of glucose

pyranose

6 membered ring

Furanose

5 membered ring

Alpha anomer

OH and CH2OH point opposite

beta anomer

OH and CH2OH in same direction

Key sugar derivatives

amino sugars

NH2 replace OH e.g. glucosamine, N-acetal glucosamine/ GlcNAc

deoxy sugars

H replaces OH e.g. 2-deoxy-D-ribose in DNA

sugar acids

carbonyl/ terminal alcohol oxidised to carboxyl e.g. D-Glucaronate, sialic acid

phosphorylated sugars

Addition of phosphate traps sugar inside cells & activates e.g. glucose 6-phosphate

reducing sugar

leaves one C-1 anomeric carbon free

Anomeric carbon not attached to anything

non-reducing sugar

Locks both amomeric carbons in its glycosidic bond

key dissacharides

maltose

glucose + glucose

Alpha 1-4 linkage

Reducing

lactose

Glucose + galactose

Beta 1-4 linkage

Reducing

Sucrose

Glucose + fructose

Alpha 1 - beta 2 linkage

Non reducing

homopolysaccharides

single monomer type

amylose (starch)

alpha 1-4 glucose

Linear

Plant energy storage

amylopectin (starch)

alpha 1-4 glucose w alpha 1-6 branches Every 24-30 residues

Glycogen

Alpha 1-4 glucose wth alpha 1-6 branches every 8-12 residues

Animal energy storage

Cellulose

beta 1-4 glucose

Linear

Plant cell wall

chitin

beta 1-4, N-acetylglucosamine (GlcNAc)

Linear fibres

Exoskeleton

Fungal walls

Heteropolysaccharide

multiple monomer units

agarose

Alternating galactose units

Algae wall

Peptidoglycan

Alternating GlcNAc & Mur2Ac w peptide cross links

Glycosaminoglycans

Linear heteropolysaccharides of repeating disaccharide w high neg charges

hyaluronate

GlcA + GlcNAx

Lubricant in joints & ECM framework (extracellular matrix)

chondroitin sulfate

Shock absorption in cartilage

Keratin sulfate

in bone, cartilage & cornea

heparin

Highly sulfate

Anticoagulant

Glycoconjugates

Protoeglycans

protein attached to glycosaminoglycan

E.g. syndecans & glypicans

ECM architecture

glycoproteins

Proteins attached to short branched oligosaccharides

linkage in glycoproteins

o-linked

serine or threoinine

N-linked

asparagine

what determines ABO blood groups

glycolipids & gangliosides

O blood group

Base core

A blood group

GalNAc addition

B blood group

Gal addition