Mitosis Stages

Expansion

PMAT:

• P - Prophase: chromatin condenses into visible chromosomes, the nuclear envelope breaks down, centrosomes migrate to the poles and the spindle forms
• M - Metaphase: chromosomes align on the metaphase plate, attached at the centromere by kinetochores
• A - Anaphase: sister chromatids separate and move to opposite poles
• T - Telophase: chromosomes decondense, nuclear envelopes reform, followed by cytokinesis

Interphase precedes it: G1 (growth), S (DNA synthesis), G2 (preparation), with G0 as the resting state.

“Metaphase is where you photograph the chromosomes.” Karyotyping arrests cells in metaphase with colchicine, which prevents spindle formation.

Checkpoints guard the transitions: the G1/S checkpoint governed by p53 and Rb is the most important, arresting damaged cells for repair or apoptosis, which is why p53 loss is so oncogenic.

Drugs targeting mitosis

• Vinca alkaloids (vincristine): inhibit microtubule polymerisation, arresting in metaphase
• Taxanes (paclitaxel): stabilise microtubules, preventing separation
• Colchicine: inhibits polymerisation, used in gout for its effect on neutrophils