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MTC15: STRUCTURE OF CARBOHYDRATES AND MUCINS
01/10/07
LEARNING OUTCOMES
Describe the basic structural characteristics of polysaccharides and how they contribute to the structure of mucous
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Multiple carbohydrates join together to form disaccharides (two simple sugars), oligosaccharides (two
to ten simple sugars) and polysaccharides (many sugars)
Simple sugars have both linear and ring forms and join together via glycosidic links formed between
two –OH groups with the elimination of a water molecule
Epimers are hexoses with –H and –OH groups on opposite sides near C1, e.g. glucose and mannose
Sugars also have D and L forms (dextro and levo) which depend on the orientation of the asymmetric
carbon farthest away from C1; e.g. in glucose, if the –OH on C5 is on the right of the molecule then it is
D-glucose
In the ring form, sugars have α and β forms which are determined by the orientation of C1: if the –OH
is group is below the ring structure then it is the α form, otherwise it is the β form
Aldoses (e.g. glucose) have an aldehyde group on C1; ketoses (e.g. fructose) have a ketone group on
(or after) C2
Amino sugars have an amide (NH2) group replacing an –OH group, e.g. glucosamine (α-amide group on
C2)
Uronic acids have a carboxyl (COOH) group in the C6 position, e.g. glucuronic acid
Sugar alcohols are hydrogenated (aldoses or ketoses), e.g. glucitol (sorbitol), and have about half the
calories of standard sugars
Sucrose is a common table sugar composed of glucose and fructose joined by an α1-β2 linkage
Lactose is the main sugar found in milk composed of galactose and glucose joined by a β1-4 linkage
Maltose is the product of starch hydrolysis composed of two glucoses joined by an α1-4 linkage
Describe how the functions of basic biological molecules are determined by their structure
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Starch is an α-D-glucose polysaccharide used for energy storage and has two different forms: amylose
and amylopectin (roughly 1:3 ratio)
Amylose is linear and joined by 1α-4 linkages
Amylopectin is branched with branches forming 1α-6 linkages
Glycogen is another branched polysaccharide (with similar bonds to amylopectin) composed of
glucose which is found in liver, muscle and brain cells and is used a mid-term storage polymer (e.g.
overnight)
The extra-cellular matrix within which all our bodies’ cells reside is composed of hyaluronic acid which
carries a negative charge in solution, thus attracting sodium which in turn attracts water and thereby
hydrates it into a gel
Glycosylation is the addition of carbohydrates to other molecules (e.g. proteins to form glycoproteins)
Most proteins acquire 14 sugar residues including N-acetyl-glucosamine, mannose and glucose by
glycosylation on entering the ER
N-linked glycoproteins have a carbohydrate chain attached to an asparagine amino acid (ASN)
O-linked glycoproteins have a carbohydrate chain attached to a serine / threonine amino acid
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Mucus is roughly 95% water and between 1 and 10% glycoproteins with trace amounts of salts,
proteins, lipids, carbohydrates, nucleic acids and secretory IgA
Mucins are large, heavily glycosylated proteins that are either membrane bound (non-gel forming,
e.g. MUC1) or gel forming (form sticky solutions, e.g. MUC2)