The interconversion of DHAP and GAP greatly favors the formation of DHAP. Yet th

Question

The interconversion of DHAP and GAP greatly favors the formation of DHAP. Yet the conversion of DHAP by triose phosphate isomerase proceeds readily. Why? Why is the regulation of phosphofructokinase by energy charge not as important in the liver as it is in the muscle? Why can't the reactions of glycolytic pathway simply be run in reverse to synthesize glucose? Why are their irreversible reactions in glycolysis? The intravenous infusion of fructose into healthy volunteers leads to a two- to fivefold increase in the level of lactate in the blood, a far greater increase than that observed after the infusion of the same amount of glucose, (a). Why is glycolysis more rapid after the infusion of fructose? (b) Fructose has been used in place of glucose for intravenous feeding. Why is this use of fructose unwise? What is feedback inhibition? Why is it a useful property? Give an example of feedback inhibition. Name and describe 2 metabolic disorders. Show the pathways and deficiencies that are associated with the diseases. Be thorough so that a non-biochemistry can understand your answer. The Brain does not have insulin receptors. Why? Describe lactose intolerance and the mechanism that is associated with the disorder.

Explanation / Answer

Ans.1) DHAP and GAP are isomers of each other and can readily inter-convert by the action of the enzyme triose-phosphate isomerase. It is true that the interconversion of DHAP and GAP greatly favors the formation of DHAP. Because the GAP formed is removed immediately by subsequent reactions, resulting in the conversion of DHAP into GAP by the enzyme.

2.) The regulation of phosphofructokinase by energy charge not as important in the liver as it is in muscle due to the fact that the energy needed for muscle fluctuate widely; from rest to intense exercise. Accordingly, the regulation of phosphofructokinase by energy charge is essential. Whereas in liver, ATP concentration is less prone to fluctuate and it is not the main regulator of phosphofructokinase.

3.) In glycolysis, the reactions catalyzed by hexokinase, phosphofructokinase and pyruvate kinase are irreversible. These enzymes have regulatory along with the catalytic roles. They have regulatory function hence they are irreversible and responsible for proper execution of glycolysis. If these enzyme find any discrepancy, they immediately stops the further reactions.

4.a) Glycolysis is more rapid after the infusion of fructose because the F-1P pathway produces glyceraldehyde 3-phosphate.

b.) It is unwise to use fructose in place of glucose for intravenous feeding because phosphofructokinase, a key control enzyme is bypassed in this situation.

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