In glycolytic pathway which of the following steps shows reduction of co-enzyme

Options

A. 1,3-diphosphoglycerate to 3-phosphogly-create
B. Glucose 6-Phosphate to fructose 6-phosphate
C. 3-Phosphogylcerate to 2-phosphogylcerate
D. Glyceraldehyde 3-phosphate to 1-3, diphosphoglycerate.

Answer

To determine which step in the glycolytic pathway shows the reduction of coenzyme NAD+, we need to analyze each of the provided options step by step.

### Step-by-Step Solution:

1. **Understanding the Coenzyme**:
- The coenzyme involved in the glycolytic pathway is NAD+ (nicotinamide adenine dinucleotide). It acts as an electron carrier and gets reduced to NADH during specific reactions in glycolysis.

2. **Analyzing Each Option**:
- **Option 1**: **1,3-bisphosphoglycerate to 3-phosphoglycerate**.
- In this step, ATP is produced, but no NADH is generated. Therefore, this option does not show the reduction of NAD+.

- **Option 2**: **Glucose 6-phosphate to fructose 6-phosphate**.
- This step involves an isomerization reaction, and no NADH is produced. Thus, this option also does not show the reduction of NAD+.

- **Option 3**: **3-phosphoglycerate to 2-phosphoglycerate**.
- This step does not involve any reduction of NAD+. No NADH is produced here either, making this option incorrect.

- **Option 4**: **Glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate**.
- In this step, glyceraldehyde 3-phosphate is oxidized, and NAD+ is reduced to NADH. This is the step where the reduction of the coenzyme occurs.

3. **Conclusion**:
- The correct answer is **Option 4**: Glyceraldehyde 3-phosphate converts to 1,3-bisphosphoglycerate, where NAD+ is reduced to NADH.

### Final Answer:
**Option 4**: Glyceraldehyde 3-phosphate when converted to 1,3-bisphosphoglycerate shows the reduction of coenzyme NAD+.