Carbohydrates

Question 1

What is a carbohydrate?

Answer 1

Substances that contain carbon, hydrogen and oxygen.

Question 2

How is a disaccharide formed?

Answer 2

A disaccharide is made by joining two monosaccharides in a condensation reaction, where a H2O is lost, forming a glycosidic bond.

Question 3

Relate the structure of starch and glycogen to their function.

Answer 3

• Large molecule
  Insufficient H bond interactions with water to dissolve molecule as hydroxyl groups form H bonds with e/o –> Insoluble in water –> ideal storage material
• Composed of many a glucose monomers
  Act as a large store of carbon and energy
• Compact shape
  a 1,4 glycosidic bonds –> helical coil –> structure is compact –> many glucose residues can be stored in a small vol. –> ideal for storage
• Stable
  hydroxyl groups of glucose residues projected into interior of helices –> form H bonds with e/o to stabilise shape
• Organisation of chains
  Not cross linked –> can be readily hydrolysed to release monomers
  Starch: a 1,4 glycosidic bonds of amylose, amylopectin hydrolysed by enzymes + a 1,6 glycosidic bonds

Glycogen:

Question 4

Relate the structure of cellulose to their function.

Answer 4

• Large molecule
  Insoluble in water –> ideal structural material
• Each cellulose chain is a straight chain
• Straight chains make inter-chain bonding most effective as there are more areas of contact.
• Chains associated in groups to microfibrils and macrofibrils.

Question 5

What is the bond angle between two C - O bonds in starch?

Answer 5

109

Question 6

What is starch made of?

Answer 6

Amylose and amylopectin.

Question 7

Describe the bonding in amylose.

Answer 7

a glucose residues joined by a 1,4 glycosidic bonds, where the angle formed between two C - O bonds is 109, forming a helical shape.

Hydroxyl group (-OH) on carbon-2 of each glucose residue projects into the middle and form H bonds with each other, stabilising shape of amylose polymer —> holding helical shape

Question 8

Describe the bonding in amylopectin.

Answer 8

α-glucose monomers are joined by either α 1, 4 glycosidic bonds or α 1, 6 glycosidic bonds. α 1, 6 glycosidic bond causes branch points in the polymer.

Question 9

Relate the large molecule of starch to its function.

Answer 9

Large molecule indicates that starch is insoluble in water -> ideal storage molecule as there is little effect on its water potential