In which of the following steps NADH can be produced?
Glucose → fructose
Citric acid → isocitric acid
Pyruvic acid → Acetyl CO~A
OAA → citric acid

Options

A. Glucose `to` fructose
B. Citric acid `to` isocitric acid
C. Pyruvic acid `to` Acetyl `CO~A`
D. OAA `to` citric acid

Answer

To determine in which of the following steps NADH can be produced, we will analyze each reaction step by step:

1. **Glucose → Fructose**:
- This conversion involves the phosphorylation of glucose to fructose, which does not produce NADH. Instead, ATP is converted to ADP in this step.
- **Hint**: Look for reactions that involve the reduction of NAD+ to NADH.

2. **Citric Acid → Isocitric Acid**:
- This step is an isomerization reaction where citric acid is converted to isocitric acid. It involves the rearrangement of the molecule but does not produce NADH.
- **Hint**: Isomerization reactions typically do not involve electron carriers like NAD+.

3. **Pyruvic Acid → Acetyl CoA**:
- In this reaction, pyruvic acid (or pyruvate) is converted into acetyl CoA. During this process, NAD+ is reduced to NADH, and carbon dioxide (CO2) is released. This is a key step in cellular respiration where NADH is produced.
- **Hint**: Look for decarboxylation reactions where NAD+ is reduced.

4. **OAA → Citric Acid**:
- In this step, oxaloacetic acid (OAA) is converted to citric acid. This reaction involves the addition of acetyl CoA to OAA and does not produce NADH.
- **Hint**: This is a condensation reaction that typically does not involve the reduction of NAD+.

**Conclusion**: The only step in which NADH is produced is the conversion of pyruvic acid to acetyl CoA.

**Final Answer**: The correct answer is **C: Pyruvic Acid → Acetyl CoA**.

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