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Cells & Molecules > Cell Division
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Cell division

  • Occurs in the nucleus of eukaryotic cells by mitosis and meiosis
    • Replacement of the entire lining of your small intestine
    • Liver cells only divide for repairing
    • Nerve cells do not divide

Chromosomes

  • Long and thin for replication and decoding
  • Become short and fat prior mitosis → easier to separate due to compact form

Meiosis (reduction division)

  • During the production of sex cells (gametes) in animals
  • In spore formation which precedes gamete production in plants
  • Haploid gametes (sperm ovum) - sexual reproduction
  • DNA in a cell replicates only once, but cell divides twice

The Cell Cycle

  • Interphase
    • G1: Protein synthesis and growth (10 hours)
      • Preparation for DNA replication (e.g. growths of mitochondria)
      • Differentiation, only selected genes are used to perform different functions in each cell
    • S: DNA Replication (9 hours)
    • G2: short gap before mitosis, organelles and proteins for mitosis are made (4 hours)
  • G0: Resting phase (nerve cells)
  • M-phase
    • Mitotic division of the nucleus (Prophase, Metaphase, Anaphase, Telophase)
    • Cytokinesis (division of the cytoplasm)

Interphase

  • Phase with highest metabolism (mitochondria have a high activity)
  • Muscles never complete the whole cycle

Mitosis

  • Process of producing 2 diploid daughter cells with the same DNA by copying their chromosomes (clones)
  • Chromosomes can be grouped into homologous pairs
  • Mitosis occurs in
    • Growth
    • Repair
    • Replacement of cells with limiting life span (red blood, skin cells)
    • Asexual replacement
  • Controlled process, cancers result from uncontrolled mitosis of abnormal cells
  • Division of the nucleus (karyokinesis) and the cytoplasm (cytokinesis) are two processes of mitosis
  • Division of cytoplasm after nucleus. Delayed if cells have more than one nucleus (muscle)
  • Active process that requires ATP

Prophase

  • Chromosomes become shorter and thicker by coiling themselves (condensation)
  • This prevents tangling with other chromosomes
  • Nuclear envelope disappears/breaks down
  • Protein fibres (spindle microtubules) form
  • Centrioles are moving toward opposite poles forming the spindle apparatus of microtubule

Metaphase

  • Centrioles at opposite poles
  • Chromosomes line up on the equator of the spindle
  • Centromeres (kinetochores) attach to spindle fibres
  • Kinetochores consist of microtubules and "motor" proteins which utilise ATP to pull on the spindle

Anaphase

  • Spindle fibres pull copies of chromatids to spindle poles to separate them
  • Mitochondria around spindle provide energy for movement

Telophase

  • Chromatid at the pole
  • Sets of chromosomes form new nuclei
  • Chromosomes become long and thin, uncoil!
  • Nuclear envelopes form around the nucleus