What happens to the citric acid cycle when thiamine pyrophosphate (TPP), a cofactor for pyruvate dehydrogenase, is deficient?

💡 Explanation

A deficiency in thiamine pyrophosphate (TPP) impairs the activity of pyruvate dehydrogenase, which is required to convert pyruvate to acetyl-CoA. Because acetyl-CoA is a key input for the citric acid cycle, the cycle's activity decreases significantly; therefore, option C is correct, rather than increased ATP production or unaltered amino acid metabolism.

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