Correctly identify the energy -yielding step of glycolysis .

Options

A. 2 - phosphoglycerate to 2- phosphoenolpyruvate
B. Fructose 1,6 - bisphosphate to PGAL and DHAP
C. Fructose to fructose -6- phosphate
D. Phosphoenolpyruvic acid to pyruvic acid

Answer

To solve the question regarding the energy-yielding step of glycolysis, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Glycolysis**: Glycolysis is a metabolic pathway that converts glucose into pyruvate, producing energy in the form of ATP and NADH. It occurs in the cytoplasm of cells.

2. **Identify the Steps of Glycolysis**: Glycolysis consists of several steps, including:
- Conversion of glucose to glucose-6-phosphate
- Conversion of glucose-6-phosphate to fructose-6-phosphate
- Conversion of fructose-6-phosphate to fructose-1,6-bisphosphate
- Splitting of fructose-1,6-bisphosphate into two three-carbon molecules (DHAP and PGAL)
- Conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate
- Conversion of 2-phosphoglycerate to 2-phosphoenolpyruvate
- Conversion of phosphoenolpyruvate to pyruvate

3. **Identify Energy-Yielding Steps**: In glycolysis, energy is produced during specific steps:
- The conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate involves substrate-level phosphorylation, yielding ATP.
- The conversion of phosphoenolpyruvate to pyruvate also yields ATP, catalyzed by the enzyme pyruvate kinase.

4. **Evaluate the Given Options**:
- The options provided in the question include various steps of glycolysis. We need to identify which of these steps is an energy-yielding step.
- The step where phosphoenolpyruvate (PEP) is converted to pyruvate is the final step that yields energy (ATP).

5. **Conclusion**: The correct answer is the step where phosphoenolpyruvate is converted to pyruvate, as this is where ATP is produced.

### Final Answer:
The energy-yielding step of glycolysis is the conversion of phosphoenolpyruvate to pyruvate.

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