Phase of cell cycle when DNA polymerase is active

Options

A. `G_(1)`
B. S
C. `G_(2)`
D. M

Answer

### Step-by-Step Solution:

1. **Understanding the Cell Cycle**: The cell cycle consists of two main phases: the mitotic (M) phase and interphase. Interphase is further divided into three sub-phases: G1, S, and G2.

2. **Identifying the Phases**:
- **G1 Phase**: This is the first gap phase where the cell grows and carries out normal metabolic functions. DNA replication does not occur here.
- **S Phase**: This is the synthesis phase where DNA replication takes place. DNA polymerase, the enzyme responsible for synthesizing new DNA strands, is active during this phase.
- **G2 Phase**: This is the second gap phase where the cell continues to grow and prepares for mitosis. DNA replication has already been completed by this phase.
- **M Phase**: This phase includes mitosis and cytokinesis, where the cell divides into two daughter cells. DNA replication is not occurring here.

3. **Conclusion**: Since DNA polymerase is responsible for DNA replication, and DNA replication occurs during the S phase, the correct answer to the question is the **S Phase**.

### Final Answer:
The phase of the cell cycle when DNA polymerase is active is the **S Phase**.

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