Question

Which of the following coenzymes/prosthetic groups are required by PDH complex for its functioning ? A. NAD
B. TPP
C. FMN
D. FAD
E. ATP
Choose the correct answer from the options given below :

• A. \(A, B, C, D\) only
• B. \(A, B, C, E\) only
• C. \(B, C, D, E\) only
• D. \(A, B, D\) only

Hint:

Remember the five cofactors of PDH complex: \[ \text{TPP, Lipoamide, CoA, FAD, NAD}^+ \] Mnemonic: \[ \textbf{TLCFN} \]
• T \(\rightarrow\) TPP
• L \(\rightarrow\) Lipoamide
• C \(\rightarrow\) CoA
• F \(\rightarrow\) FAD
• N \(\rightarrow\) NAD\(^+\)

Answer 1

The Correct Option is D

Concept: The Pyruvate Dehydrogenase (PDH) complex catalyzes the conversion: \[ \text{Pyruvate} \rightarrow \text{Acetyl-CoA} \] This reaction links: \[ \text{Glycolysis} \quad \text{and} \quad \text{TCA cycle} \] The PDH complex requires several cofactors/coenzymes for its activity. Major cofactors include:
• TPP (Thiamine pyrophosphate)
• Lipoamide
• Coenzyme A
• FAD
• NAD\(^+\)

Step 1: Evaluating statement A. Statement A: \[ \text{NAD} \] This is correct. NAD\(^+\) acts as an electron acceptor during oxidation reactions in the PDH complex. Thus: \[ \boxed{A \text{ is correct}} \]

Step 2: Evaluating statement B. Statement B: \[ \text{TPP} \] This is correct. TPP (derived from vitamin \(B_1\)) is required by: \[ E_1 \text{ component of PDH} \] for decarboxylation of pyruvate. Thus: \[ \boxed{B \text{ is correct}} \]

Step 3: Evaluating statement C. Statement C: \[ \text{FMN} \] This is incorrect. FMN is mainly associated with: \[ \text{Complex I of ETC} \] and not with the PDH complex. Thus: \[ \boxed{C \text{ is incorrect}} \]

Step 4: Evaluating statement D. Statement D: \[ \text{FAD} \] This is correct. FAD functions in the: \[ E_3 \text{ component} \] of PDH complex during electron transfer reactions. Thus: \[ \boxed{D \text{ is correct}} \]

Step 5: Evaluating statement E. Statement E: \[ \text{ATP} \] ATP is not a coenzyme or prosthetic group required directly for PDH catalysis. Thus: \[ \boxed{E \text{ is incorrect}} \] Therefore, the required coenzymes/prosthetic groups are: \[ \boxed{A, B, D} \] Hence, the correct answer is: \[ \boxed{(D)\ A, B, D \text{ only}} \]