Question

During which phase of the cell cycle does DNA replication occur?

• A. \(G_1\) phase
• B. S phase
• C. \(G_2\) phase
• D. M phase

Hint:

Remember the sequence \(G_1 \rightarrow S \rightarrow G_2 \rightarrow M\). The S phase is the only phase where DNA synthesis occurs.

Answer 1

The Correct Option is B

Concept: The cell cycle is the sequence of events through which a cell grows and divides. It consists of:

• Interphase

• M phase (Mitosis)
Interphase is further divided into: \[ G_1 \rightarrow S \rightarrow G_2 \]

Step 1: Understand the \(G_1\) phase. The cell grows in size and synthesizes proteins and organelles. No DNA replication occurs here.

Step 2: Understand the S phase. The letter S stands for Synthesis. During this phase:

• DNA molecules replicate.

• Chromosomes duplicate.

• Genetic material doubles.
As a result, each chromosome forms two sister chromatids.

Step 3: Understand the \(G_2\) phase and M phase. In \(G_2\), the cell prepares for division. In M phase, mitosis occurs and chromosomes are distributed into daughter cells. Thus, DNA replication takes place only during the S phase.