2.2 all cells arise from other cells

• describe the stages of the cell cycle in eukaryotic cells

  interphase - (S phase) DNA replicates semi-conservatively

  leading to 2 chromatids (identical copies) joined at a centromere

  (G1/G2) number of organelles and volume of cytoplasm increases, protein synthesis

  mitosis - nucleus divides

  to produce 2 nuclei with identical copies of DNA produced by parent cell

  cytokinesis - cytoplasm and cell membrane (normally) divide

  to form 2 new genetically identical daughter cells
• mitosis stage 1 (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
• mitosis stage 2 (metaphase)

  spindle fibres attach to chromosomes by their centromeres

  chromosomes align along equator
• mitosis stage 3 (anaphase)

  spindle fibres shorten/contract

  centromere divides

  pulling chromatids (from each pair) to opposite poles of cell
• mitosis stage 4 (telophase)

  chromosomes uncoil becoming longer/thinner

  nuclear envelopes reform so 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 a cell cycle
• explain the importance of mitosis in the life of an organism

  parent cell divides to produce 2 genetically identical daughter cells for:

  growth of multicellular organisms by increasing cell number

  replacing cells to repair damage tissues

  asexual reproduction
• describe how tumors 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 and 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)

  replication of circular DNA

  replication of plasmids

  division of cytoplasm to produce 2 daughter cells

  single copy of circular DNA

  variable number of copies of plasmids
• describe how viruses replicate

  attachment proteins attach complementary receptors on host cell

  inject viral nucleic acid (DNA/RNA) into host cell

  infected host cell replicates virus particles

  nucleic acid replicated

  cell produces viral protein/capsid/enzymes

  virus assembled then released