The number of ATP molecules produced by electron transport system from Krebs cycle intermediates in a single trun is

Options

A. 11
B. 12
C. 14
D. 16

Explanation

To determine the number of ATP molecules produced by the electron transport system from Krebs cycle intermediates in a single turn, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reduced Coenzymes Produced**: In one turn of the Krebs cycle, three molecules of NADH2 and one molecule of FADH2 are produced. Additionally, one molecule of GTP is generated through substrate-level phosphorylation.

2. **ATP Production from NADH2**: Each molecule of NADH2, when oxidized in the electron transport chain, produces 3 ATP molecules. Since 3 NADH2 are produced in one turn of the Krebs cycle:
- ATP from NADH2 = 3 NADH2 × 3 ATP/NADH2 = 9 ATP

3. **ATP Production from FADH2**: Each molecule of FADH2, when oxidized, produces 2 ATP molecules. Since 1 FADH2 is produced in one turn of the Krebs cycle:
- ATP from FADH2 = 1 FADH2 × 2 ATP/FADH2 = 2 ATP

4. **ATP Production from GTP**: GTP can be readily converted to ATP, so we consider the GTP produced as equivalent to 1 ATP:
- ATP from GTP = 1 ATP

5. **Total ATP Production**: Now, we sum up all the ATP produced from NADH2, FADH2, and GTP:
- Total ATP = ATP from NADH2 + ATP from FADH2 + ATP from GTP
- Total ATP = 9 ATP + 2 ATP + 1 ATP = 12 ATP

Thus, the total number of ATP molecules produced by the electron transport system from Krebs cycle intermediates in a single turn is **12**.

### Final Answer:
The number of ATP molecules produced by the electron transport system from Krebs cycle intermediates in a single turn is **12**.

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