Which of the following steps during glycolysis is associated with utilisation of ATP?

Options

A. Glucose `rarr` Glucose -6-phosphate
B. Fructose-6-phosphate `rarr` Fructose-1,6-biphosphate
C. PEP `rarr` Pyruvic acid
D. Both (a) and (b)

Explanation

To answer the question about which steps during glycolysis are associated with the utilization of ATP, we can break down the glycolysis process step by step.

### Step-by-Step Solution:

1. **Understanding Glycolysis**: Glycolysis is the metabolic pathway that breaks down glucose into pyruvate, producing energy in the form of ATP. It consists of two main phases: the energy investment phase and the energy payoff phase.

2. **Energy Investment Phase**: The first part of glycolysis is known as the energy investment phase. In this phase, ATP is consumed to convert glucose into more reactive forms.

3. **Conversion of Glucose to Glucose 6-Phosphate**:
- The first step involves the conversion of glucose to glucose 6-phosphate.
- This reaction is catalyzed by the enzyme **hexokinase**.
- During this step, one molecule of ATP is used, which is converted to ADP.

4. **Conversion of Glucose 6-Phosphate to Fructose 6-Phosphate**:
- Glucose 6-phosphate is then converted to fructose 6-phosphate by the enzyme **isomerase**.
- This step does not involve ATP utilization.

5. **Conversion of Fructose 6-Phosphate to Fructose 1,6-Bisphosphate**:
- The next step involves converting fructose 6-phosphate to fructose 1,6-bisphosphate.
- This reaction is catalyzed by the enzyme **phosphofructokinase**.
- Again, one molecule of ATP is utilized in this step, which is converted to ADP.

6. **Summary of ATP Utilization**:
- The two steps in glycolysis that utilize ATP are:
- Conversion of glucose to glucose 6-phosphate (using hexokinase).
- Conversion of fructose 6-phosphate to fructose 1,6-bisphosphate (using phosphofructokinase).

### Final Answer:
The steps during glycolysis that are associated with the utilization of ATP are:
1. Conversion of glucose to glucose 6-phosphate.
2. Conversion of fructose 6-phosphate to fructose 1,6-bisphosphate.