Q.Define cell cycle.

The correct order of the cell cycle is G1, then S, then G2, then M.

The eukaryotic cell cycle is divided into interphase (the period between two successive divisions, during which the cell is metabolically active but not dividing) and M phase (mitosis, where actual division occurs). Interphase itself is subdivided into three sequential sub-phases:

• G1 (Gap 1): the cell grows, is metabolically active, and synthesises RNA/proteins needed for the coming S phase; the cell is NOT yet replicating DNA.
• S (Synthesis): DNA replication occurs; the amount of DNA per cell doubles, but the chromosome number stays the same (each chromosome now has two sister chromatids).
• G2 (Gap 2): further growth and synthesis of proteins needed for mitosis (e.g., tubulin for the spindle) takes place; the cell prepares to divide. …

The cell cycle proceeds in the fixed order G1 (growth) → S (DNA synthesis) → G2 (preparation for division) → M (mitosis/cell division).

The cell cycle is divided into Interphase and M Phase (Mitotic phase):

Interphase (the 'resting' phase, though the cell is metabolically very active) is further divided into three sub-phases, in strict order:

• G1 phase (Gap 1): the cell grows, synthesises RNA and proteins, and prepares for DNA replication.
• S phase (Synthesis): DNA replication occurs, doubling the amount of DNA; the chromosome number remains the same but each chromosome now has two chromatids.
• G2 phase (Gap 2): further protein synthesis and cell growth occur, and the cell prepares the machinery needed for mitosis. …