Cell Cycle

• MTOCs

  Centrosomes in animal cells
• MTOCs

  • Found outside the nucleus during interphase
  • 1 MTOC per cell
  • Replicated during S phase so there are 2 MTOCs before cell division
• CDK

  An enzyme that activates proteins and regulates the cell cycle by phosphorylation
• Mitosis

  1. Prophase: Chromatin condenses into chromosomes. Nuclear envelope breaks down

  2. Prometaphase: Mitotic spindle forms. Microtubules connect to kinetochores

  3. Metaphase: Chromosomes line up down the middle

  4. Anaphase: Kinetochore microtubules shorten, polar microtubules lengthen

  5. Telophase: Nuclear envelope redevelops. Chromosomes decondense into chromatin
• Interphase


  Most of the cell's life is in this phase
• Cell cycle checkpoints

  1. G1: Ensures everything is ready for DNA synthesis. Assesses cell growth and favorable conditions

  2. S phase: DNA is replicated

  3. G2: Rapid cell growth; organelles replicate. Evaluates accuracy of DNA replication and checks for sufficient mitosis promoting factors
• In meiosis 1, the number of cells is doubled but the number of chromosomes stays the same
• In meiosis 2, it acts similarly to mitosis as the number of chromosomes does not get reduced
• Chromosome numbers in mitosis

  • Prophase: 46
  • Metaphase: 46
  • Anaphase: 92
  • Telophase: 92
  • Daughter cells: 46 each
• Chromosome numbers in meiosis 1

  • Prophase: 46
  • Metaphase: 46
  • Anaphase: 46
  • Telophase: 46
  • Daughter cells: 23 each
• Chromosome numbers in meiosis 2

  • Prophase: 23
  • Metaphase: 23
  • Anaphase: 46
  • Telophase: 46
  • Daughter cells: 23 each