Cell Division

• Binary fission

  • Replication of DNA
  • Replication of plasmids
  • Division of cytoplasm to produce 2 daughter cells
  • Each with single copy of circular DNA
• main sections of the cell cycle

  • Interphase
  • Mitosis
• growth stages of interphase

  • G1 phase: cell increases in size, makes new organelles and proteins, carries out its normal functions
  • S phase: DNA is replicated by semi-conservative replication
  • G2 phase: cell carries out its normal metabolic funtions but also starts making spindle proteins preparing for cell division, ATP production is increased
• Stages of mitosis

  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Prophase

  • Chromosomes condense by supercoiling and folding
  • Nucleolus disappears
  • centrioles move to opposite poles forming a network on spindle fibres across it called the spindle apparatus
  • Nuclear envelope breaks down and chromosomes lie free in the cytoplasm
• Metaphase

  • One or more spindle fibres attach to the centromere of each chromosome
  • Chromosomes line up in a sngle file at the equator
• Anaphase

  • Spindle fibres shorten causing the centromeres to divide
  • Sister chromatids move to opposite poles
  • Chromatides are known as chromosomes as they move independently to each other
• Telophase


  • 2 sets of chromosomes form at each pole
  • New nuclear envelope forms around each set of chromosomes
  • Chromosomes de-condense, becoming long and thin forming chromatin
  • Nucleolus starts to reform
  • Cytokinesis occurs
• Cytokinesis


  • Cytoplasm starts to divide
  • cell membrane is pulled inwards across the centre of the cell, pinching off the cytoplasm into 2 equal halves
  • 2 daughter cells form which are genetically identical to the original cell and each other
• Stage A is prophase - the chromatin condenses

  Stage B is anaphase - the sister chromatids are pulled apart to the poles of the cell

  
• high mitotic index means many cells are undergoing mitosis