When does synthesis of DNA end ?

Options

A. S-phase
B. Prophase
C. Premitotic gap phase
D. Post mitotic gap phase

Answer

To answer the question "When does synthesis of DNA end?", we can break down the cell cycle into its phases and identify where DNA synthesis occurs.

### Step-by-step Solution:

1. **Understand the Cell Cycle Phases**: The cell cycle consists of several phases: G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis).

2. **Identify the S Phase**: The S phase is specifically known as the Synthesis phase, where DNA replication occurs. During this phase, the cell synthesizes a complete copy of the DNA in its nucleus.

3. **Determine the End of DNA Synthesis**: DNA synthesis begins at the start of the S phase and continues until the end of the S phase. Once the DNA has been fully replicated, the synthesis is complete.

4. **Transition to G2 Phase**: After the S phase is completed and DNA synthesis is finished, the cell transitions into the G2 phase. If DNA synthesis is not complete, the cell cannot move to the G2 phase.

5. **Conclusion**: Therefore, the synthesis of DNA ends at the completion of the S phase.

### Final Answer:
The synthesis of DNA ends in the S phase of the cell cycle.

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