If 2 acetyl CoA molecues are fed into the Kreb's cycle, how many ATP molecules are synthesised directly in the cycle?

Options

A. 2
B. 4
C. 36
D. 38

Answer

To determine how many ATP molecules are synthesized directly in the Krebs cycle when 2 acetyl CoA molecules are fed into the cycle, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Acetyl CoA and the Krebs Cycle**:
- Acetyl CoA is a key substrate that enters the Krebs cycle (also known as the citric acid cycle).
- Each acetyl CoA molecule combines with oxaloacetate to form citric acid.

2. **Krebs Cycle Overview**:
- The Krebs cycle involves a series of reactions that convert citric acid into various intermediates, ultimately regenerating oxaloacetate.
- During these reactions, energy-rich molecules such as NADH, FADH2, and GTP (which can be converted to ATP) are produced.

3. **Direct ATP Production**:
- For each turn of the Krebs cycle (which corresponds to one acetyl CoA), one molecule of GTP is produced.
- GTP is energetically equivalent to ATP, meaning that 1 GTP can be converted to 1 ATP.

4. **Calculating for 2 Acetyl CoA**:
- Since each acetyl CoA results in the production of 1 GTP, feeding 2 acetyl CoA molecules into the Krebs cycle will yield:
- 2 GTP (from 2 turns of the cycle).
- Therefore, this is equivalent to 2 ATP.

5. **Final Answer**:
- The total number of ATP molecules synthesized directly in the Krebs cycle from 2 acetyl CoA molecules is **2 ATP**.

### Summary:
When 2 acetyl CoA molecules enter the Krebs cycle, **2 ATP molecules** are synthesized directly.