ch3

• purposes of cell replication

  restoring the nucleus to cytoplasm ratio, growth and development, maintenance and repair
• eukaryotic cell


  mitosis - division of nucleus, cytokeneisis, checkpoints during DNA replication, increase in organelles, longer process
• prokaryotic cell


  binary fission - circular DNA chromosome, simpler and faster, no nucleus or membrane-bound organelles
• phases in interphase


  G1, GO, S, G2
• G1 phase


  1st growth stage

  gains energy, protein and membrane synthesis, increase in organelles, cell doubles
• GO phase


  resting phase

  pathway to cell differentiation, for incompatible conditions, can only carry out normal functions
• S phase


  synthesis phase

  chromosomes are replicated by DNA replication
• G2 phase


  2nd growth stage

  gain energy and metabolism, synthesis of proteins
• prophase


  chromosomes become visible due to super coiling, centrioles move to opposite poles, microtubuoles assemble to form spindles, nucleolus becomes invisible, nuclear membrane appears
• metaphase


  chromosomes move to equator of the cell, centromeres attach to microtubuoles of spindles
• anaphase


  contraction of spindle fibres, chromatids seperate and move to opposite poles
• telophase


  chromosomes at opposite poles of the cell, spindle fibres disappear, nuclear membrane appears, nucleolus becomes visible, chromosomes uncoil and become chromatin
• cytokeneisis


  cytosol and organelles divide, 2 identical daughter cells
• checkpoints


  G1, G2, M
• G1


  towards the end of the G1 cycle

  adequate resources, DNA, size, undamaged DNA, security guard is tumor-surpressing protein (p53)

  goes to GO phase if unready for division or damaged
• G2


  at the end of G2

  replicated DNA is complete and undamaged, adequate resources
• M


  end of metaphase

  sister chromatids are attached the correct microtubuoles, chromatids are aligned correctly at the equator (even division of DNA)
• contact inhibition


  crowding and contact with neighbouring cells cause a cell to slow or stop
• mitogens


  signal for cell division
• environmental conditions


  temperature, pH, nutrients
• apoptosis


  activation of caspases (enzymes)

  digestion of cell content

  cell shrinkage

  cell bubbling and shrinkage

  removal of fragments by phagocytosis (white blood cell)
• when + why does apoptosis occur

  extrinsic pathway - end of cell lifespan, cell damage, cell stress, infection with pathogens or toxins

  intrinsic pathway - DNA damage in nucleus
• necrosis


  triggered by physical damage, toxins, pathogens, hypoxia, often with large clusters of cells
• malfunctions in apoptosis


  too much cell death will result in loss of vital tissue, too little cell death may result in tumors, cancer, etc

  genetic, proto oncogenes, p53, inherited genes, environmental factors
• cancer


  unregulated and abnormal cell growth and devision
• tumor suppressor gene p53


  checks for DNA damage
• stem cells


  yet to specialise, capable of self-renewal, allow body to develop, grow, and repair tissues
• cell potency


  totipotent, pluripotent (embryonic), multipotent (adult), unipotent (adult)