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AP Biology · Unit 4: Cell Communication & Cell Cycle

4.6 Cell Cycle

Interphase

Most of the cell cycle is interphase, when the cell grows and prepares to divide. It has three parts: G1 (growth), S (DNA is replicated), and G2 (more growth and preparation). By the end, the cell has a full duplicate copy of its DNA.

Mitosis and cytokinesis

The mitotic phase divides the nucleus through mitosis — prophase, metaphase, anaphase, telophase — followed by cytokinesis (division of the cytoplasm). During anaphase, sister chromatids are pulled apart. The result is two genetically identical cells.

Key terms

Interphase
The longest part of the cell cycle (G1, S, G2) where the cell grows and copies DNA.
S phase
The interphase stage when DNA is replicated.
Mitosis
Nuclear division (prophase, metaphase, anaphase, telophase) making two identical nuclei.
Anaphase
The stage when sister chromatids separate toward opposite poles.
Cytokinesis
Division of the cytoplasm, producing two separate cells.

Try an AP-style question

Data

A cell has 12 chromosomes in G1.

How many chromosomes and chromatids does it have at the end of S phase?

  1. 24 chromosomes and 48 chromatids
  2. 12 chromosomes and 24 chromatids
  3. 24 chromosomes and 24 chromatids
  4. 12 chromosomes and 12 chromatids
Show the answer

B. S phase copies DNA: each chromosome now has two sister chromatids, but the chromosome number (counted by centromeres) is still 12.

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