Cell Cycle Overview: Interphase and Mitosis

Interphase

  • G1: cell decides whether to divide or exit the cell cycle and differentiate.
  • S: DNA replication occurs (DNA synthesis).
  • G2: growth phase; cell prepares for M phase.

M phase

  • M phase includes mitosis (nuclear division) and cytokinesis (cytoplasm division). Timing can overlap with mitosis and cytokinesis.

Key terminology

  • Chromosome: DNA in its most compact form.
  • Chromatin: DNA in its less condensed form.
  • Chromosome condensation: chromatin condenses into chromosomes during the cell cycle.
  • Replicated vs unreplicated chromosome:
    • Unreplicated: single chromatid.
    • Replicated: two sister chromatids held at the centromere.
  • Sister chromatids: two identical copies of a chromosome after replication.
  • Centromere: region where sister chromatids are held together.
  • Kinetochores: protein structures at the centromere that attach to the mitotic spindle.
  • Centrosome: microtubule organizing center; composed of two centrioles; two centrosomes form during mitosis.
  • Centrioles: components of the centrosome.
  • Homologous chromosomes: one chromosome from each parent; same genes, may have different alleles; form a homologous pair.

Mitosis: five subphases

  • Prophase
    • Chromosomes condense; kinetochores form at the centromeres.
    • Mitotic spindle begins to form; two centrosomes move to opposite poles; each centrosome contains two centrioles.
  • Prometaphase
    • Nuclear envelope breaks down.
    • Chromosomes attach to the mitotic spindle via kinetochores.
  • Metaphase
    • Chromosomes align along the middle of the cell (metaphase plate).
  • Anaphase
    • Sister chromatids separate and are pulled toward opposite poles; chromatids become individual chromosomes.
  • Telophase
    • Nuclei reform around each set of chromosomes; spindle disassembles; cytokinesis often begins.

Cytokinesis

  • Division of the cytoplasm, resulting in two separate cells.
  • A contractile ring forms a cleavage furrow that pinches the cell membrane, completing division.

Outcome

  • After mitosis and cytokinesis: two genetically identical daughter cells, each with a full set of chromosomes in its nucleus.