For packing of a negatively charged DNA, a positively charged histone molecules rich in basic amino acids are required. This histones are formed during :

Options

A. `G_1` - phase
B. `G_2` - phase
C. S - phase
D. `G_0` - phase

Answer

To solve the question regarding when histone proteins are formed during the cell cycle, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding DNA and Histones**:
- DNA is negatively charged, while histones are positively charged proteins rich in basic amino acids. This positive charge allows histones to bind to DNA, facilitating its packaging into a compact structure called chromatin.

2. **Identifying the Cell Cycle Phases**:
- The cell cycle consists of two main phases: Interphase and M phase (mitosis).
- Interphase is further divided into three phases: G1 (Gap 1), S (Synthesis), and G2 (Gap 2).

3. **Analyzing Each Phase**:
- **G1 Phase**: The cell grows and prepares for DNA replication but does not synthesize DNA or histones.
- **S Phase**: This is the phase where DNA replication occurs. During this phase, not only is the DNA replicated, but histone proteins are also synthesized to package the newly formed DNA.
- **G2 Phase**: The cell continues to grow and prepares for division, but no new histones are synthesized during this phase.

4. **Conclusion**:
- Since histones are synthesized during the S phase when DNA replication occurs, the correct answer to the question is that histones are formed during the S phase of the cell cycle.

### Final Answer:
Histones are formed during the **S phase** of the cell cycle.

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