What happens in synthesis phase during cell cycle:-

Options

A. DNA stnthesis
B. Chromosome number becomes double
C. Formation of two nuclei
D. Synthesis of tubulin proteins

Answer

### Step-by-Step Solution:

1. **Understanding the Cell Cycle**: The cell cycle consists of several phases, including G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis). Each phase has specific functions that prepare the cell for division.

2. **Identifying the S Phase**: The S phase is specifically the synthesis phase of the cell cycle. It is crucial for DNA replication.

3. **DNA Replication**: During the S phase, the cell's DNA is replicated. This means that each chromosome is duplicated, resulting in two identical copies (sister chromatids) for each chromosome.

4. **Chromosome Number**: As a result of DNA replication, the chromosome number effectively doubles. For example, if a cell starts with 46 chromosomes, it will have 92 chromatids at the end of the S phase.

5. **Formation of Nuclei**: The S phase also prepares the cell for the formation of two nuclei. This is a preparatory step for mitosis, where the cell will eventually divide into two daughter cells.

6. **Protein Synthesis**: In addition to DNA replication, the S phase involves the synthesis of proteins necessary for cell division. This includes proteins such as tubulin, which are essential for forming the mitotic spindle.

7. **Transition to G2 Phase**: After the S phase, the cell enters the G2 phase, where it continues to grow and prepares for mitosis.

### Summary of the S Phase:
- **DNA Synthesis**: DNA is replicated, doubling the chromosome number.
- **Formation of Sister Chromatids**: Each chromosome is duplicated, resulting in two identical copies.
- **Preparation for Mitosis**: The cell prepares for the formation of two nuclei.
- **Protein Synthesis**: Tubulin and other proteins are synthesized to facilitate cell division.