Polysaccharides

Polysaccharides – describe the polysaccharides; starch, glycogen, cellulose, chitin, hyaluronic acid, chondroitin sulphate and peptidoglycan – with regards to general structures and function

Types:

1. Homoglycan: polymers of one type of monosaccharide

2. Heteroglycan: polymers of more than one type of monosaccharide

Synthesized

Polysaccharides are synthesised without a template by the addition of monosaccharide’s and disaccharides

Result

The length of polysaccharides therefore varies ie. Not fixed – like proteins

Classified:

According to their biological role

Eg – glycogen and starch = storage polysaccharide + cellulose and chitin = structural polysaccharides

Differ.

* In type of polysaccharides involved

* In their linkages

1. Starch – Mixture of amylase and amylopectin

A. Structure of amylase (100-1000 D glucose residues)

B. Structure f amylopectin (branched from amylose)

Glycogen:

* Has the same structure

* But, branches are smaller and more frequent – more compact molecule

* More residue molecules involved

How will these molecules be digested? – Amylases hydrolyse a: 1→4 glucosidic bonds

2. Cellulose – D-glucose residues

Strength and rigidity of cellulose fibrils is the result of intra- and inter- hydrogen bonds

* Flatter structure

* Form plants

* Tight packing

3. Chitin (is a polysaccharide of N-acetylglucosamine)

* Exoskeleton of insects and crustaceans; cell walls of fungi and algae

4. Heteroglycans: Glyconjugates

* Proteoglycans (proteins + glycosaminoglycans)

* Peptidoglycans (peptides + (GlcNAc-MurNAc)n)

* Glycoproteins (proteins + various polysaccharides)

→ Glycolipids

A. Glycosaminoglycan – repeat dissacharide unit of amino sugars (GlcNAc or GalNAc) and alduronic acid AND –OH or –NH2 sometimes sulphated – polyanionic (-S- and –COO-)

Eg Hyaluronic acid

Therfore, Bind with a protein = Proteoglycan

* Proteoglycan aggregate of cartilage

Polysaccharide of...