Answers to questions on Carbohydrates

1. Methanal only contains two of the three distinguishing features of a carbohydrate. In addition to containing a carbonyl group and an empirical formula of CH₂O carbohydrates must also contain at least two -OH groups.

2. Source of energy; storage of energy, precursors (for other important biological molecules) and dietary fibre

3. The –OH group on the fifth carbon atom forms an ether linkage with the first carbon atom and the carbonyl group is converted into an alcohol.

4. Amylose is a straight chain polymer formed by condensing α-D-glucose units via α-1,4 glycosidic linkages. Although it contains many polar -OH groups it is arranged in helical structure so cannot easily hydrogen bond to water molecules. Amylopectin has a branched structure as it contains both α-1,4 and α-1,6 linkages. Because of the branched structure the molecules can more easily form hydrogen bonds with water molecules.

5.

6. Dietary fibre is mainly plant material that is not hydrolysed by enzymes secreted in the human digestive tract but may be digested by microflora in the gut. Dietary fibre may help to prevent: (any three from) diverticulosis, prevention of irritable bowel syndrome, constipation, obesity, Crohn's disease, haemorrhoids, diabetes mellitus.

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