Cell cycle

What are the phases in the cell cycle?

G1, S, G1, M

Where are the checkpoints?

G1, S (DNA synthesis checkpoint), G2, and M (metaphase)

G1

(Gap 1) The first growth phase where the cell increases in size, synthesizes proteins, and monitors its environment before committing to DNA replication

S phase

The critical stage where DNA replication occurs. Each chromosome is duplicated to form two sister chromatids

G2

(Gap 2) The second growth period where the cell produces organelles and proteins (like tubulin) necessary for chromosome movement

G0

A "resting" or quiescent state where cells exit the cycle and do not divide. This can be temporary or permanent (e.g., mature nerve cells).

G1 Checkpoint

(The Restriction Point) The most important "go/no-go" decision. The cell checks for DNA damage, cell size, and growth factors. If it fails, it may enter G0 or undergo apoptosis.

S & G2 Checkpoint

Ensures that all DNA has been replicated accurately and completely without damage before entering the Mitotic (M) phase. The one at S-phase is called Dna Synthesis checkpoint.

M Checkpoint

(Spindle Checkpoint) Occurs during metaphase. The cell ensures all sister chromatids are correctly attached to the spindle microtubules before anaphase begins.

Time lengths

G1 = 10-12 hours

S phase = 6-8 hours

G2 = 3-4 hours

M phase = 1 hour