The Cell Cycle and Mitosis, Explained
How a single cell becomes two identical daughter cells — the phases of the cell cycle, the stages of mitosis, the checkpoints that keep division under control, and why failures lead to cancer.
Updated 2026-06-02
Why cells divide
Every multicellular organism grows, repairs wounds, and replaces worn-out cells through cell division. The cell cycle is the ordered sequence of events that takes one cell, doubles its contents, and splits it into two genetically identical daughter cells. Get the order and the controls right and you understand most of how tissues build and maintain themselves.
The cycle has two broad parts: interphase, the long preparatory phase where the cell grows and copies its DNA, and the mitotic (M) phase, where the duplicated chromosomes are separated and the cell physically divides.
The phases of the cell cycle
Most of a cell's life is spent in interphase, preparing to divide.
G1 phase
The cell grows, makes proteins, and carries out its normal functions while monitoring conditions for division.
S phase
DNA is replicated, so each chromosome now consists of two identical sister chromatids.
G2 phase
The cell continues growing and produces the proteins needed for division, then checks for DNA damage.
Mitosis (M)
The nucleus divides and sister chromatids are pulled to opposite poles.
Cytokinesis
The cytoplasm splits, producing two separate daughter cells.
G0 phase
A resting state where some cells exit the cycle, either temporarily or permanently.
The four stages of mitosis
A useful mnemonic: Prophase, Metaphase, Anaphase, Telophase — "PMAT."
Prophase
Chromatin condenses into visible chromosomes, the nuclear envelope breaks down, and the spindle begins to form.
Metaphase
Chromosomes line up single-file along the cell's equator, attached to spindle fibers from both poles.
Anaphase
Sister chromatids are pulled apart to opposite poles, ensuring each daughter cell gets a complete set.
Telophase
Chromosomes decondense, nuclear envelopes reform around each set, and the cell prepares to split.
How to study it (the efficient way)
Master interphase before mitosis
Most students rush to PMAT and forget that G1, S, and G2 are where the cell grows and copies its DNA.
Use the PMAT mnemonic
Lock the order of the four mitotic stages, then attach one defining event to each.
Draw it, don't just read it
Sketch chromosome behavior at each stage — a mind map or diagram beats re-reading the textbook.
Connect checkpoints to cancer
Understanding what the G1, G2, and M checkpoints guard against makes the whole topic click — and it is heavily tested.
Common questions
How is mitosis different from meiosis?
Mitosis produces two identical diploid cells for growth and repair; meiosis produces four genetically varied haploid gametes for reproduction.
What are checkpoints?
Control points (mainly at G1, G2, and within mitosis) where the cell verifies conditions are right before proceeding. They prevent damaged or incomplete cells from dividing.
What happens when the cell cycle goes wrong?
Loss of checkpoint control allows cells with DNA damage to keep dividing, which is the underlying mechanism of cancer.
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