Question

52. Catabolism of fatty acids stimulates gluconeogenesis in all of the following ways EXCEPT:

1. By contributing to the production of NADH
2. By providing carbons for the glucose skeleton
3. By activating pyruvate carboxylase
4. By contributing to the production of ATP
5. By producing Acetyl-CoA

55. [NADPH/NADP+] is maintained at a high level in cells primarily by:

1. Lactate dehydrogenase
2. The combined actions of glucose -6 phosphate dehydrogenase and gluconolactonase
3. The action of the electron transport chain
4. Shuttle mechanisms as the α-glycerophosphate dehydrogenase shuttle
5. The combined actions of transketolase and transaldolase

56. If a cell requires more ribose-5-phosphate than NADPH:

1. Only the first phase of the pentose phosphate pathway would occur
2. Glycolytic intermediates would flow into the reversible phase of the pentose phosphate pathway
3. There would be sugar interconversions but no net release of carbons from glucose-6- phosphate
4. The equivalent of the carbon atoms to glucose-6-phosphate would be released as 6CO₂
5. Only part of this need could be met by the pentose pathway and the rest would have to be supplied by another pathway.

Answer 1

1.

Correct answer is (A).

Explanation :-

The high concentration of NADH inhibits gluconeogenesis by preventing the oxidation of lactate to pyruvate. In fact, the high concentration of NADH will cause the reverse reaction to predominate, and lactate will accumulate. So it does not stimulate gluconeogenesis.

(B) is wrong answer because it has written By providing carbons for the glucose skeleton, which is correct statement.

(C) is wrong answer because it has written By activating pyruvate carboxylase, which is correct statement.

(D) is wrong answer because it has written By contributing to the production of ATP , which is correct statement.

(E) is wrong answer because it has written By producing Acetyl-CoA, which is correct statement.

Explanation :-

Fatty acid oxidation is important for gluconeogenesis, although fatty acid carbon cannot be used for glucose, fat oxidation provides both an energy source (ATP) to support gluconeogenesis and acetyl coenzyme A (acetyl-CoA) to activate pyruvate carboxylase.

2.

Correct answer is (B).

Explanation :-

[NADPH/NADP+] is maintained at a high level in cells primarily by The combined actions of glucose -6 phosphate dehydrogenase and gluconolactonase.

(A) is wrong answer because it has written Lactate dehydrogenase, which is incorrect statement.

(C) is wrong answer because it has written The action of the electron transport chain, which is incorrect statement.

(D) is wrong answer because it has written Shuttle mechanisms as the α-glycerophosphate dehydrogenase shuttle, which is incorrect statement.

(E) is wrong answer because it has written The combined actions of transketolase and transaldolase, which is incorrect statement.

3.

Correct answer is (B).

Explanation :-

When more R5P is needed than NADPH, R5P can be formed through glycolytic intermediates. Glucose 6-phosphate is converted to fructose 6-phosphate (F6P) and glyceraldehyde 3-phosphate (G3P) during glycolysis. Transketolase and transaldolase convert two molecules of F6P and one molecule of G3P to three molecules of R5P. During rapid cell growth, higher quantities of R5P and NADPH are needed for nucleotide and fatty acid synthesis, respectively. Glycolytic intermediates can be diverted toward the non-oxidative phase of PPP by the expression of the gene for pyruvate kinase isozyme, PKM. PKM creates a bottleneck in the glycolytic pathway, allowing intermediates to be utilized by the PPP to synthesize NADPH and R5P. This process is further enabled by triosephosphate isomerase inhibition by phosphoenolpyruvate, the PKM substrate.

(A) is wrong answer because it has written Only the first phase of the pentose phosphate pathway would occur , which is incorrect statement.

(C) is wrong answer because it has written There would be sugar interconversions but no net release of carbons from glucose-6- phosphate, which is incorrect statement.

(D) is wrong answer because it has written The equivalent of the carbon atoms to glucose-6-phosphate would be released as 6CO2 , which is incorrect statement.

(E) is wrong answer because it has written Only part of this need could be met by the pentose pathway and the rest would have to be supplied by another pathway , which is incorrect statement.

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