Biomolecules

Question 1

Why are starch and glycogen good storage polysaccharides

Answer 1

• large and thus insoluble water so they do not exert osmotic effect
• large and unable to diffuse out of cell
• fold into compact shape so large amounts can be stored within a fixed volume
• easily hydrolysed by enzymes when the monosaccharides are needed by the cell

Question 2

Structure of amylopectin

Answer 2

• branched chain polymer
• several thousand a- glucose residues which are linked by a-1,4- glycosidic bonds and a-1,6-glycosidic bonds where branch points occurs
• coils into a helical, compact structure stabilised by H bonds
• -OH group on carbon 2 projects into the middle of the helix and hydrogen bonds formed between hydroxyl group of adjacent glucose residues

Question 3

Structure of amylose

Answer 3

• unbranched chain polymer
• several thousand a-glucose residues which are linked by a-1,4-glycosidic bonds
• coil into helical, compact structure stabilised by H bonds
• -OH group on carbon 2 of each glucose residue projects into the middle of the helix and hydrogen bonds are formed between the -OH groups of adjacent glucose residues

Question 4

Structure of glycogen

Answer 4

• a-glucose residues linked by a-1,4-glycosidic bonds and a-1,6-glycosidic bonds where branch point occurs
• more extensive branching than amylopectin, thus a more compact structure
• coils into a helical, compact structure stabilised by H bonds

Question 5

Structure of cellulose

Answer 5

• unbranched chain monomer
• consists of B-glucose linked by B-1,4-glycosidic bonds
• adjacent glucose monomers are rotated 180° wrt each other
• straight chains of b-glucose run parallel to each other with numerous hydrogen bonds
• intra-chain H bonds occur between -OH and O of adjacent molecules
• interchain H bonds occur between -OH groups projecting outwards from each chain and O of parallel chain
• this cross linking binds the chains rigidly together
• cellulose chains associate in groups to form bundles called microfibrils which are arranged in larger bundles to form macrofibrils
• macrofibrils of successive layers are interwoven and embedded in gel-like matrix, creating High tensile strength