Carbohydrates of physiological importance

Question 1

Sugars can exist as either ketoses or aldoses. Name some aldoses.

Answer 1

• glyceraldehyde (glycerose)
• erythrose
• lyxose
• xylose
• arabinose
• ribose
• glucose
• mannose
• galactose

Question 2

Sugars can exist as either ketoses or aldoses. Name some ketoses.

Answer 2

• dihydroxyacetone
• xylulose
• ribulose
• fructose
• sedoheptulose

Question 3

What are the physiologically important hexose sugars? Why?

Answer 3

• glucose (primary source of fuel in humans)
• fructose (second best source of fuel in humans - can be converted to glucose)
• mannose (used in glycoproteins)
• galactose (thirs best source of fuel in humans - cna be converted ot glucose; needed for lactose production in breast milk, used to make glycolipids, glycoproteins etc.)

Question 4

Define the following terms:

• inulin
• dextrin
• cellulose
• glycogen
• chitin
• pectin

Answer 4

1. inulin is a polysaccharide of fructose; because it is not broken down by intestinal enzymes it is not nutritionally significant
2. Dextrins are intermediates in the hydrolysis of starch
3. Cellulose - polymer found in plant cell walls made up of 1,4 - glycosidic linkages
4. glycogen is the ‘starch equivalent’ in humans; it is made up of amylopectin (branched chains with 1,6 glycosidic linkages) and amylose (helix with 1,4 glycosidic linkages)
5. Chitin - structural polysaccharide in exoskeleton of hard-shelled creatures i.e. crustaceans - it is a polymer of N-acetyl-D-glucosamine monomers with 1,4 glycosidic bonds
6. Pectin is a polymer of galacturonic acid linked by 1,4 glycosidic bonds