Regeneration of each RuBP in ` C_(3)` cycle requires

Options

A. 1 ATP
B. 6 ATP
C. 1 ATP and 1 NADPH ` + H^(+)`
D. 3 ATP and 2 NADPH ` + H^(+)`

Answer

To solve the question regarding the regeneration of each RuBP (ribulose bisphosphate) in the C3 cycle, we need to understand the steps involved in the Calvin cycle and the resources required for the regeneration of RuBP. Here’s a step-by-step breakdown of the process:

### Step-by-Step Solution:

1. **Understanding the C3 Cycle**:
- The C3 cycle, also known as the Calvin cycle, is a series of biochemical reactions that occur in the chloroplasts of plants. It is responsible for carbon fixation, where carbon dioxide is converted into organic compounds.

2. **Role of RuBP**:
- RuBP (ribulose 1,5-bisphosphate) acts as a carbon dioxide acceptor. When carbon dioxide enters the cycle, it combines with RuBP to form a 6-carbon intermediate that quickly splits into two molecules of 3-phosphoglycerate (3-PGA).

3. **Conversion of 3-PGA to G3P**:
- The 3-PGA molecules are then phosphorylated and reduced to form glyceraldehyde 3-phosphate (G3P). This step requires ATP and NADPH.

4. **ATP and NADPH Usage**:
- For every 12 molecules of 3-PGA formed, 12 ATP and 12 NADPH are consumed to convert them into G3P.

5. **Regeneration of RuBP**:
- Out of the 12 G3P molecules produced, 10 are used to regenerate RuBP, while 2 G3P molecules are used to synthesize glucose.
- The regeneration of 10 G3P molecules back to 6 RuBP requires 6 ATP molecules.

6. **Calculating ATP Requirement for One RuBP**:
- Since 6 ATP are needed to regenerate 6 RuBP, it follows that to regenerate 1 RuBP, only 1 ATP is required.

### Final Answer:
The regeneration of each RuBP in the C3 cycle requires **1 ATP**.

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