Carbohydrate chemistry for medical students

1. Carbohydrate chemistry CH##
By Dr M.H Abdelzaher

23. • Cellulose
• It is the most abundant polysaccharide in nature.
• It is a simple polysaccharide formed of β- 1 ---4 glycoside bonds.
• It is a straight chain. The non-branching character and β – linkages are
responsible of its fibrous and tough nature as well as its water insolubility.
• It is the main structural molecules in cell walls of plants. Cotton is almost
pure cellulose.
• Cellulose cannot be digested by most animals as the β – 1 4 linkages are
not hydrolyzed by α amylase (The only vertebrates able to use cellulose as
food are cattle and other ruminant animal as sheep, goats and camel).
• Undigested cellulose forms a part of undigestible components of the
diet known as dietary fibres which has different actions (effect on the rate
of absorption of nutrients, reduction of plasma cholesterol, decreasing
absorption of toxic compounds and reduce the incidence of cancer
colonand prevention of constipation).

25. • Other homopolysaccharides:
• Chitin:
• It is the second most abundant polysaccharide in nature after
cellulose.
• It is linear composed of N-acetylglucosamine residues linked
together by B glycoscidic linkages, undigestable , principle
component of hard exoskeleton of most arthrpods as insects and
crabs.
• Inulin:
• It is formed of repeated units of β- fructose (fructosans).
• It cannot be digested or metabolized by humans.
• It is used as a marker of glomerular filtration rate “renal function
test”.
• Agar agar: formed of repeated units of galactose.
• It is used as a culture medium for bacteria.

36. Proteoglycans are proteins that contain many chains of glycosaminoglycans.
Importance of proteoglycans

39. • Can be attached to proteins with one of two configurations:
• 1- O-linked - carbohydrate bonded to -OH of serine or
threonine
• 2- N-linked - carbohydrate (usually N-acetylglucosamine)
linked to asparagines