Question

Ratio of ATP:NADH:FADH2 produced in Krebs' cycle per one acetyl Co-A molecule by substrate level phosphorylation is:

• A. 2 : 3 : 2
• B. 1 : 9 : 2
• C. 2 : 9 : 2
• D. 2 : 2 : 9

Hint:

Understanding the output of the Krebs' cycle is crucial for comprehending the overall energy yield of cellular respiration, especially how glucose is fully oxidized to harness energy.

Answer 1

The Correct Option is B

To solve the problem, we need to determine the ratio of ATP produced in the Krebs cycle per one acetyl-CoA molecule by substrate-level phosphorylation, considering NADH and FADH₂.

1. Understanding the Krebs Cycle ATP Production:
In the Krebs cycle, each acetyl-CoA molecule undergoes a series of reactions that produce high-energy molecules such as NADH and FADH₂. These molecules are then used in the electron transport chain to generate ATP through oxidative phosphorylation. However, during the Krebs cycle, some ATP is produced directly through substrate-level phosphorylation.

2. ATP Production by NADH and FADH₂:
In the Krebs cycle, for each acetyl-CoA molecule:
3 molecules of NADH are produced.
1 molecule of FADH₂ is produced.
ATP is generated through substrate-level phosphorylation, typically yielding 1 ATP per acetyl-CoA.

3. Analyzing the Options:
We are asked to find the ratio of ATP produced per acetyl-CoA molecule by substrate-level phosphorylation, taking into account NADH and FADH₂ production:
(A) 2 : 3 : 2: This ratio does not match the typical ATP yield in the Krebs cycle.
(B) 1 : 9 : 2: This is the correct ratio. The cycle produces 1 ATP (directly from substrate-level phosphorylation), 3 NADH, and 1 FADH₂.
(C) 2 : 9 : 2: This ratio is incorrect as it does not align with the expected production from one acetyl-CoA molecule.
(D) 2 : 9 : 9: This ratio is also incorrect, as the number of ATP and FADH₂ produced do not align with the typical yield from one acetyl-CoA molecule.

Final Answer:
The correct answer is Option B: 1 : 9 : 2.