Q.Describe the three sequential phases of interphase -- G1, S and G2 -- briefly stating the principal event that characterises each.

[!TLDR]

G1: growth, no DNA synthesis. S: DNA replicates, doubling DNA content. G2: further growth, synthesis of division proteins.

[!ANSWER]

G1 -- growth and normal metabolic activity, DNA not yet replicated. S -- DNA replication, doubling the DNA content; centriole also duplicates. G2 -- further growth and synthesis of the proteins (e.g. spindle tubulin) needed for mitosis.

Interphase is divided into three sequential sub-phases. In G1 (Gap 1), the longest and most variable sub-phase, the cell grows, carries out its normal metabolic activities, and synthesises the proteins and RNA needed for growth, while its nuclear DNA remains a single, unreplicated copy per chromosome. In S phase (Synthesis), the defining event of interphase occurs: the entire nuclear DNA is replicated, so that each chromosome becomes duplicated into two sister chromatids and the total DNA content of the cell doubles; in animal cells the centriole also duplicates during S phase. In G2 (Gap 2), the cell undergoes a further period of growth and synthesises the specific proteins, including the tubulin subunits of spindle microtubules, that will be required for the mechanical process of mitosis, completing its preparation for division.

[!ANSWER]

G1 -- growth and normal metabolic activity, DNA not yet replicated. S -- DNA replication, doubling the DNA content; centriole also duplicates. G2 -- further growth and synthesis of the proteins (e.g. spindle tubulin) needed for mitosis.

Assign exactly one defining event to each of the three sub-phases in order: growth (G1), replication (S), preparation for division (G2).

Describing S phase as when the cell 'divides' -- S phase only replicates DNA; the cell does not physically divide until much later, in M phase.