Metabolism of carbohydrates

Question 1

Deficiency of what enzyme leads to hemolytic anemia?

Answer 1

Glucose-6-phosphate dehydrogenase

Question 2

What three monosaccharides are absorbed from the GIT?

Answer 2

• Glucose
• Galactose
• Fructose

Question 3

The pentose phosphate pathway is alternative means of metabolising glucose. What products are formed in this pathway and what is not formed?

Answer 3

• NADPH and ribose are produced

- ATP is not produced

Question 4

The pentose phosphate pathway occurs in which part of the cell?

Answer 4

Cytosol, just like glycolysis

Question 5

Why does deficiency in glucose-6-phosphate dehydrogenase cause hemolytic anemia?

Answer 5

Glucose-6-phosphate dehydrogenase is needed in the pentose phosphate pathway to produce NADPH. This NADPH then serves in reducing glutathione so that it can break down H2O2 into H2O.

A deficiency in this enzyme means that NADPH cannot be produced and hence glutathione cannot break down H2O2, hence it accumulates and destroys RBCs, causing hemolysis. This leads to hemolytic anemia.

Question 6

The uronic acid pathway is an alternative way of metabolising glucose, in addition to the pentose phosphate pathway. Ascorbic acid (vitamin C) is one of the products in this pathway. What is the direct precursor to vitamin C?

Answer 6

L - gulonate

Question 7

Humans cannot synthesise vitamin C via the uronic acid pathway and must obtain it from diet. Why is this so?

Answer 7

L-gulonate is the direct precursor of vitamin C - ascorbic acid and is converted to vitamin C by the enzyme gulonolactone oxidase. Humans lack this enzyme, and hence cannot make ascorbic acid