Biomolecules Question 124
Question: There is no net synthesis of glucose from fatty acids, because of the irreversible nature of the reaction.
Options:
A) Pyruvate to oxaloacetate
B) Pyruvate to acetyl CoA
C) Phosphoenol pyruvate to puruvate
D) Oxaloacetate to phosphoenol pyruvate
Show Answer
Answer:
Correct Answer: B
Solution:
[b] The reaction sequence, glucose $ \to $ pyruvate $ \to $ acetyl CoA $ \to $ fatty acid is possible because, the reaction pyruvate $ \to $ acetyl CoA is catalysed by pyruvate dehydrogenase.
The reaction is absolutely irreversible.
Fat is degraded to acetyl CoA; this 2 carbon unit enters into the TCA cycle, where 2 carbon atoms are oxidised to 2 molecules of carbon dioxide; hence no net conversion of fat to carbohydrate is possible.
However, glycerol part of neutral fat and propionyl CoA (3 carbon unit) from odd chain fatty acids can generate glucose; but quantitatively these are minimal sources.
BETA
