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The cell cycle consists of interphase and mitosis. Interphase is the preparatory phase where the cell grows, replicates DNA, and duplicates organelles. It is subdivided into the G1, S, G2 phases, plus the quiescent G0 state.
During G1, the cell increases its protein synthesis to reach the appropriate size. Protein concentration averages ~100 mg mL⁻¹, and ribosome biogenesis ramps up to meet the demand. A cell cannot progress to S phase until ribosome numbers are sufficient. Toward the end of G1, mitochondria fuse into an efficient network, enhancing ATP production.
S phase is dedicated to DNA replication. Because DNA is packaged with histone proteins, new histones are produced in tandem with the copied strands. This coupling ensures that newly synthesized DNA is immediately wrapped. Concurrently, phospholipid synthesis doubles, replenishing membranes for the upcoming mitotic spindle and organelle division.
In G2, the cell completes organelle duplication and performs a final quality‑control check. The genome is now twice the size of the G1 genome, and the cell verifies that DNA integrity is intact—no breaks or nicks. The G2‑M checkpoint is the last decision point before the cell commits to mitosis.
G0 represents a reversible exit from the cycle. Cells that differentiate into specialized, non‑dividing types enter G0 and become terminally differentiated. Nonetheless, certain stimuli can reactivate G0 cells, returning them to G1 and permitting division.
For a deeper dive, see Cell cycle – Wikipedia.
