Q.(a) Explain the interphase of mitotic cell cycle. OR

Interphase is the long, metabolically active phase between two mitotic divisions, during which the cell grows and its DNA is replicated, split into the G1, S, and G2 sub-phases.

The mitotic cell cycle is divided into INTERPHASE (the resting/preparatory phase, no visible chromosome division) and M PHASE (mitosis proper, where the cell actually divides). Interphase, though appearing quiescent under a light microscope, is in fact the most metabolically active part of the cycle, occupying about 90-95% of its total duration, and consists of three sub-phases:

1. G1 (Gap 1) phase: the cell grows in size, synthesizes RNA and proteins, and increases the number of organelles, preparing the machinery needed for DNA replication.

2. S (Synthesis) phase: the cell's DNA is replicated - each chromosome duplicates to form two identical sister chromatids joined at the centromere. The amount of DNA doubles, though the chromosome NUMBER stays the same at this stage.

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