Eukaryotic Cell Cycle

• Main stages of the eukaryotic cell cycle

  • Mitosis
  • Cytokinesis
  • Interphase
• Interphase


  Cellular growth and duplication of chromosomes
• Mitosis


  Separation of sister chromatids and formation of 2 new nuclei
• Cytokinesis


  Division of cytoplasm and formation of 2 new daughter cells
• Interphase


  Cells synthesise necessary DNA, proteins and organelles required for growth and repair
• Phases of Interphase


  • G1 phase
  • S phase
  • G2 phase
• G1 phase


  1. Increasing volume of cytosol

  2. Synthesising proteins for DNA replication

  3. Replicating organelles
• G0 phase


  Cells that are terminally differentiated and no longer undergo cell division
• S Phase


  1. Cells replicate their DNA

  2. Chromosomes go from single stranded to double stranded
• Sister chromatids


  Held together at the centromere
• Human somatic cells are diploid
• Diploid cells contain pairs of chromosomes
• Humans have 23 pairs of chromosomes, therefore 2 x 23 = 46 chromosomes total
• After S phase, cells will still have 46 chromosomes as they are counted by the number of centromeres present
• G2 Phase


  1. Further increasing cytosol volume

  2. Synthesising proteins in preparation of mitosis
• Mitosis involves separating the newly divided double stranded chromosomes into 2 sets of single stranded chromosomes
• Cytokinesis separates cytoplasm and divides into 2 new daughter cells
• Steps in Mitosis


  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Prophase


  1. Condensation of chromatin into chromosomes

  2. Centrioles migrate to opposite poles

  3. Spindle fibres begin to form

  4. Nuclear membrane breaks down
• Metaphase


  1. Spindle fibres attach to the centromere

  2. Chromosomes are aligned at the equator
• Anaphase


  1. Spindle fibres contract and split centromeres

  2. Sister chromatids are pulled to opposite ends of cell
• Telophase


  1. Chromosomes densely pack together

  2. New nuclear membrane forms

  3. Spindle fibres disintegrate
• Cytokinesis in animals


  Cleavage Furrow develops and pinches the plasma membrane into 2 cells
• Cytokinesis in plants


  A cell plate forms first at the equator before separating into 2
• Checkpoints


  • G1 Checkpoint
  • G2 Checkpoint
  • Metaphase Checkpoint
• G1 Checkpoint


  1. Verifies if a cell has grown to correct size

  2. Has enough protein for DNA synthesis

  3. Any DNA damage
• G2 Checkpoint


  1. Verifies that DNA has replicated correctly in S Phase

  2. Has enough resources for mitosis
• Metaphase Checkpoint


  1. Verifies that spindle fibres have formed correctly

  2. Chromosomes are aligned correctly at equator