All cells arise from other cells

• What happens in the cell cycle during interphase

  • (S phase) DNA replicates semi conservaitvely
  • (G1/G2) number of organelles and volume of cytoplasm increases, protein synthesis
• What happens in the cell cycle during mitosis

  ● Nucleus divides

  ● To produce 2 nuclei with identical copies of DNA produced by parent cell
• What happens in the cell cycle during cytokinesis

  ● Cytoplasm and cell membrane (normally) divide

  ● To form 2 new genetically identical daughter cells
• Describe the behaviour of chromosomes & role of spindle fibres in Prophase

  ● Chromosomes condense, becoming shorter / thicker (so visible)

  ○ Appear as 2 sister chromatids joined by a centromere

  ● Nuclear envelope breaks down

  ● Centrioles move to opposite poles forming spindle network
• Describe the behaviour of chromosomes & role of spindle fibres in Metaphase

  ● Spindle fibres attach to chromosomes by their centromeres ● Chromosomes align along equator
• Describe the behaviour of chromosomes & role of spindle fibres in Anaphase

  ● Spindle fibres shorten / contract

  ● Centromere divides

  ● Pulling chromatids (from each pair) to opposite poles of cell
• Describe the behaviour of chromosomes & role of spindle fibres in Telophase

  ● Chromosomes uncoil, becoming longer / thinner

  ● Nuclear envelopes reform = 2 nuclei

  ● Spindle fibres / centrioles break down
• Stages of mitosis

  1. Prophase
  2. Metaphase
  3. Anaphase
  4. Telophase
• Explain the importance of mitosis in the life of an organism

  ● Growth of multicellular organisms by increasing cell number ● Replacing cells to repair damaged tissues

  ● Asexual reproduction
• Describe how tumours and cancers form

  ● Mutations in DNA / genes controlling mitosis can lead to uncontrolled cell division

  ● Tumour formed if this results in mass of abnormal cells

  ○ Malignant tumour = cancerous, can spread (metastasis)

  ○ Benign tumour = non-cancerous
• Suggest how cancer treatments control rate of cell division

  Some disrupt spindle fibre activity / formation:

  • So chromosomes can’t attach to spindle by their centromere
  • So chromatids can’t be separated to opposite poles (no anaphase)
  • So prevents / slows mitosis
  • Some prevent DNA replication during interphase:
  • So can’t make 2 copies of each chromosome (chromatids)
  • So prevents / slows mitosis
• Describe how prokaryotic cells replicate

  Binary fission:

  1. Replication of circular DNA
  2. Replication of plasmids
  3. Division of cytoplasm to produce 2 daughter cells
  4. Single copy of circular DNA
  5. Variable number of copies of plasmids
• Describe how viruses replicate

  1. Attachment proteins attach to complementary receptors on host cell
  2. Inject viral nucleic acid (DNA/RNA) into host cell
  3. Infected host cell replicates virus particles: the Nucleic acid is replicated and Cell produces viral protein / capsid / enzymes then the Virus is assembled and released