Question

Define the S phase and related events.

Answer 1

Hint: The interphase of the cell cycle has three phases - G1, S and G2 phases. The term S phase represents synthesis phase. In addition to it, it is the period where duplication of DNA occurs in the cell cycle.

Complete step by step answer: S phase can be defined as the phase of the cell cycle during which replication of DNA takes place. S phase takes place between the G1 and G2 phases of the interphase of the cell cycle. S phase is also known as the synthesis phase as it is the period which marks the synthesis of DNA. G1 phase which is also called gap 1 phase is the first phase of the cell cycle and it takes place in eukaryotic cell division. The cell cycle consists of four phases. During the G1 phase synthesis of mRNA and proteins take place required for the subsequent steps which lead to mitosis of the cell. As soon as the G1 phase ends the beginning of the S phase of the interphase is marked. The growth of cells occurs in the G1 phase. Inactive pre-replication complexes (pre-RCs) are distributed on the replication genome in the M phase and G1 phase. The cell converts pre-RCs into active replication forks which initiates DNA replication in the S phase. G2 phase also called a gap 2 phase is the third subphase of interphase in which the cell is prepared to enter into the prophase of M phase leading to mitosis.

Note: The G1 phase, S phase and G2 phase all three together form the long growth period of the cell cycle called the interphase which takes place before the M phase that is the mitosis phase. The four phases of the cell cycle include the G1 phase, S phase, G2 phase, and M phase.