The Cell Cycle (College Board AP® Biology): Study Guide

Events of the cell cycle

• In eukaryotes, cells divide and transmit genetic information during the cell cycle

  • The cell cycle is the highly regulated sequence of events that occurs between one cell division and the next

• The cell cycle has three phases:

  • interphase: during interphase the cell grows and carries out its normal cellular functions, e.g. synthesizing proteins and replicating DNA ready for mitosis

    • G1: cells grow, prepare for DNA replication and produce new organelles

    • S: DNA replication, or synthesis, takes place

    • G2: cells continue to grow and also prepare for mitosis

  • mitosis: nuclear division

  • cytokinesis: the cytoplasm and organelles are divided between the new daughter cells

Nondividing cells

• Not all cells divide all of the time; sometimes cells will stop dividing, e.g. when they are mature or when conditions for growth are not ideal

• Nondividing cells enter phase G₀, during which cell division does not occur; this exit from the cycle can occur at any stage of the cycle

• Cells in G₀ may re-enter the cell cycle in response to chemical signals

Mitosis

• Mitosis is a form of nuclear division; it ensures the transfer of a complete genome from a parent cell to the new daughter cells

• Mitosis produces two, genetically identical daughter cells

• The production of genetically identical cells by mitosis is essential for:

  • growth

  • tissue repair

  • asexual reproduction

• Mitosis is part of the cell cycle, and occurs after the completion of interphase

• The process of mitosis involves a series of steps:

  • prophase

    • the nuclear membrane breaks down

    • the chromosomes condense

    • spindle fibers begin to form

  • metaphase

    • spindle fibres attach to the centromere of each chromosome

    • the chromosomes line up along the equator of the cell

  • anaphase

    • the spindle fibres shorten, pulling the sister chromatids to opposite ends of the cell

    • the sister chromatids become chromosomes in their own right

  • telophase

    • new nuclear membranes form around the separated groups of chromosomes