All cells arise from other cells

• Describe the stage Interphase within the cell cycle:

  • (S phase) DNA replicates semi-conservatively - leading to 2 chromatids (identical copies) joined at the centromere
  • (G1/G2) number of organelles and volume of cytoplasm increases. protein synthesis
• Describe the stage mitosis within the cell cycle:

  • Nucleus divides
  • To produce two nuclei with identical copies of DNA produced by parent cell
• Describe the stage cytokinesis within the cell cycle:

  • Cytoplasm and cell membrane divide
  • To form 2 new genetically identical daughter cells
• What is the order of phases within Mitosis?

  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Describe what happens during prophase:

  • Chromosomes condense, becoming shorter and thicker (so visible) - appear as 2 sister chromatids joined by a centromere
  • Nuclear envelope breaks down
  • Centrioles move to opposite poles forming spindle fibres
• Describe what happens during metaphase:

  • Chromosomes align along equator
  • Spindle fibres attach to chromosomes by their centromeres
• Describe what happens during anaphase:

  • Spindle fibres contract
  • Centromere divides
  • Pulling chromatids (from each pair) to opposite poles of cell
• Describe what happens during telophase:

  • Chromosomes uncoil, becoming longer/thinner
  • Nuclear envelopes reform = 2 nuclei
  • Spindle fibres/centrioles break down
• Why do some eukaryotic cells not undergo the cell cycle?

  • Within multicellular organisms, not all cells retain the ability to divide (e.g. neurons)
  • Only cells that do retain this ability go through the cell cycle
• Explain the importance of mitosis in the life of an organism:

  Parent cells divide to produce 2 genetically identical daughter cells for:

  • 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 forms if this results in mass of abnormal cells

  Malignant = cancerous, can spread

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

  1)Some disrupt spindle fibre activity/formation

  • So chromosomes can't attach to spindle fibre by their centromere
  • So chromatids can't be separated to opposite poles (no anaphase)
  • So prevents/slows down mitosis

  2)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

  • Single copy of circular DNA
  • Variable number of copies of plasmids
• Describe how viruses replicate:

  1. Attachment proteins attach to complementary receptor cells on host cell
  2. Inject viral nucleic acid (DNA/RNA) into host cell
  3. Infected host cell replicates virus particles:

  a)Nucleic acid replicates

  b)Cell produces viral protein/capsid/enzymes

  c)Virus assembled then released