Question

Thiamine deficiency causes decreased energy production because:

• A. It is required for the process of transamination
• B. It is a co-factor in oxidative reduction
• C. It is a co-enzyme for transketolase in the pentose phosphate pathway
• D. It is a co-enzyme for pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase

Hint:

Think about which oxidative decarboxylations feed and drive the TCA cycle.

Answer 1

The Correct Option is D

Step 1: The active coenzyme form of thiamine (vitamin B1) is thiamine pyrophosphate (TPP).
Step 2: The question links the deficiency specifically to decreased energy (ATP) production. TPP is the essential coenzyme for two key oxidative decarboxylation steps that feed the TCA cycle and oxidative phosphorylation: pyruvate dehydrogenase (pyruvate to acetyl-CoA) and alpha-ketoglutarate dehydrogenase (alpha-ketoglutarate to succinyl-CoA).
Step 3: Loss of these two dehydrogenases blocks entry of carbon into the TCA cycle and stalls the cycle itself, so NADH/FADH2 generation and therefore ATP output fall sharply, explaining the energy deficit.
Step 4: Transketolase (option C) is also TPP-dependent but belongs to the non-oxidative pentose phosphate pathway and is the basis of the diagnostic erythrocyte transketolase test, not the main route of energy production. Thiamine is not the cofactor for transamination (that needs pyridoxal phosphate) or a general oxidation-reduction cofactor.
Conclusion: Decreased energy production is due to its role as coenzyme for pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase, option D, matching the printed key.