All cells arise from other cells

• State what the cell cycle is and outline its stages

  the cycle of division with intermediate growth periods

  1. interphase
  2. mitosis or meiosis
  3. cytokinesis
• What happens during interphase

  G1: cell synthesises proteins for replication

  S: DNA replicates

  G2: organelles divide
• State the purpose of mitosis

  produces 2 genetically identical daughter cells for:

  • growth
  • cell replacement / repair
  • asexual reproduction
• Name the stages of mitosis

  1. Prophase
  2. Metaphase
  3. Anaphase
  4. Telophase
• What happens during prophase

  chromatin condenses into chromosomes, is now visible, nucleolus disappears
• what happens during metaphase

  sister chromatids line up at the equator of the cell, spindle fibres are attached to their centromeres
• what happens during anaphase

  requires ATP energy - spindle fibres on centromeres contract, sister chromatids are separated into 2 chromosomes and are pulled to opposite poles of the cell
• what happens during telophase

  chromosomes unwind to chromatin and are invisible again

  cytoplasm divides

  new nuclear envelope forms around each set of chromosomes
• Suggest how cancer treatments control the rate of cell division

  they disrupt the cell cycle:

  • prevent DNA replication
  • disrupt spindle fibre formation
  • however can also damage healthy cells
• How do prokaryotic cells replicate?

  Binary Fission:

  1. DNA loop replicates, plasmids replicate in cytoplasm
  2. cell elongates, separating the 2 DNA loops
  3. cell membrane contracts & septum forms
  4. cell splits into 2 identical progeny cells - each with 1 copy of the DNA and a variable number of plasmids copied
• How do viruses replicate?

  1. attachment proteins attach to receptors on the host cell
  2. enveloped viruses fuse with / moves into the cell membrane via endocytosis and releases DNA / RNA into the cytoplasm or injects it
  3. host cell uses viral genetic information to divide
  4. new viral particle is copied along with cell
• How do viral particles leave the host cell

  pinch off & use the cell membrane to form envelop

  or

  cause lysis of the host cell