Question

which metabolic pathway is not reversible?
o a. the step from pyruvate to acetyl coa.
o b. the step from pyruvate to lactate.
o c. the step from acetyl coa to fatty acids.
o d. the step from pyruvate to amino acids.

Explanation:

• In glycolysis, the conversion of pyruvate to lactate (anaerobic) is reversible as lactate can be converted back to pyruvate via lactate dehydrogenase.
• The conversion of pyruvate to acetyl - CoA is irreversible. Pyruvate dehydrogenase complex catalyzes this reaction, and there is no enzyme to directly convert acetyl - CoA back to pyruvate in the reverse direction.
• The conversion of acetyl - CoA to fatty acids (through fatty acid synthesis) and the conversion of pyruvate to amino acids (transamination) are also not simple reverse reactions of the forward steps in the context of the main metabolic pathways. But the key non - reversible step among the options is the pyruvate to acetyl - CoA conversion.

Answer:

a. The step from pyruvate to acetyl CoA.