Question:
Names of the coenzymes and prosthetic groups:
A. Thiamine pyrophosphate
B. Lipoic acid
C. Pyridoxal phosphate
D. Coenzyme A
E. Nicotinamide adenine dinucleotide (NAD\(^+\))
Choose the correct coenzymes and prosthetic groups, from the above list, which are required by the Krebs cycle enzyme Pyruvate dehydrogenase:
Names of the coenzymes and prosthetic groups:
A. Thiamine pyrophosphate
B. Lipoic acid
C. Pyridoxal phosphate
D. Coenzyme A
E. Nicotinamide adenine dinucleotide (NAD\(^+\))
Choose the correct coenzymes and prosthetic groups, from the above list, which are required by the Krebs cycle enzyme Pyruvate dehydrogenase:
A. Thiamine pyrophosphate
B. Lipoic acid
C. Pyridoxal phosphate
D. Coenzyme A
E. Nicotinamide adenine dinucleotide (NAD\(^+\))
Choose the correct coenzymes and prosthetic groups, from the above list, which are required by the Krebs cycle enzyme Pyruvate dehydrogenase:
Show Hint
The Pyruvate Dehydrogenase complex requires 5 cofactors: TPP, Lipoic acid, CoA, FAD, and \(\text{NAD}^+\). Remember that Pyridoxal Phosphate (PLP) is exclusively involved in amino acid metabolism (transamination) and has no role in PDH.
Updated On: Aug 7, 2026
- A, D and E only
- A, C and E only
- A, B, D and E only
- A, B, C, D and E only
Show Solution
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The Correct Option is C
Solution and Explanation
Step 1: Understanding the Concept:
The Pyruvate Dehydrogenase (PDH) complex is a multi-enzyme assembly that links glycolysis to the Krebs cycle by catalyzing the oxidative decarboxylation of pyruvate to acetyl-CoA.
This complex requires five distinct coenzymes/prosthetic groups to carry out its multi-step catalytic mechanism.
Step 2: Detailed Explanation:
The PDH complex consists of three enzymes: Pyruvate dehydrogenase (\(\text{E}_1\)), Dihydrolipoyl transacetylase (\(\text{E}_2\)), and Dihydrolipoyl dehydrogenase (\(\text{E}_3\)).
Together, they utilize five cofactors:
1. Thiamine pyrophosphate (TPP - A): Serves as the prosthetic group bound to \(\text{E}_1\) that binds and decarboxylates pyruvate.
2. Lipoic acid (B): Acts as a covalently bound prosthetic group on \(\text{E}_2\) (lipoamide) that accepts the acetyl group from TPP and transfers it to Coenzyme A.
3. Coenzyme A (CoA-SH - D): Serves as a soluble substrate coenzyme that accepts the acetyl group to form the final product, Acetyl-CoA.
4. Flavin adenine dinucleotide (FAD): Serves as the prosthetic group bound to \(\text{E}_3\) that reoxidizes the reduced lipoamide. (Not listed in the question).
5. Nicotinamide adenine dinucleotide (\(\text{NAD}^+\) - E): Serves as a soluble coenzyme that accepts electrons from \(\text{FADH}_2\) to yield \(\text{NADH} + \text{H}^+\).
Pyridoxal phosphate (PLP - C): This is the active form of vitamin \(\text{B}_6\), which is required for amino acid transamination reactions, not for the PDH complex.
Therefore, the required cofactors from the list are A, B, D, and E.
Step 3: Final Answer:
The coenzymes required by the Pyruvate Dehydrogenase complex are A, B, D, and E only, corresponding to option (C).
The Pyruvate Dehydrogenase (PDH) complex is a multi-enzyme assembly that links glycolysis to the Krebs cycle by catalyzing the oxidative decarboxylation of pyruvate to acetyl-CoA.
This complex requires five distinct coenzymes/prosthetic groups to carry out its multi-step catalytic mechanism.
Step 2: Detailed Explanation:
The PDH complex consists of three enzymes: Pyruvate dehydrogenase (\(\text{E}_1\)), Dihydrolipoyl transacetylase (\(\text{E}_2\)), and Dihydrolipoyl dehydrogenase (\(\text{E}_3\)).
Together, they utilize five cofactors:
1. Thiamine pyrophosphate (TPP - A): Serves as the prosthetic group bound to \(\text{E}_1\) that binds and decarboxylates pyruvate.
2. Lipoic acid (B): Acts as a covalently bound prosthetic group on \(\text{E}_2\) (lipoamide) that accepts the acetyl group from TPP and transfers it to Coenzyme A.
3. Coenzyme A (CoA-SH - D): Serves as a soluble substrate coenzyme that accepts the acetyl group to form the final product, Acetyl-CoA.
4. Flavin adenine dinucleotide (FAD): Serves as the prosthetic group bound to \(\text{E}_3\) that reoxidizes the reduced lipoamide. (Not listed in the question).
5. Nicotinamide adenine dinucleotide (\(\text{NAD}^+\) - E): Serves as a soluble coenzyme that accepts electrons from \(\text{FADH}_2\) to yield \(\text{NADH} + \text{H}^+\).
Pyridoxal phosphate (PLP - C): This is the active form of vitamin \(\text{B}_6\), which is required for amino acid transamination reactions, not for the PDH complex.
Therefore, the required cofactors from the list are A, B, D, and E.
Step 3: Final Answer:
The coenzymes required by the Pyruvate Dehydrogenase complex are A, B, D, and E only, corresponding to option (C).
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