Cell Division

• Why do cells undergo mitosis?

  growth of tissues

  replacement of lost cells

  repair of damaged cells

  asexual reproduction

  formation of clones of T and B lymphocytes
• Stages of interphase

  G1, S, G2
• G1 phase


  cells growth, production of enzymes and proteins for cell growth
• S phase

  DNA synthesis
• G2 phase

  cell growth, DNA checked for errors, production of tubulin proteins for spindles fibres
• Phases of mitosis

  prophase, metaphase, anaphase, telophase
• Prophase


  chromosomes condense- become shorter and visible, nuclear envelope dissolves, centrioles move to opposite poles of the cell

  
• Metaphase


  chromosomes align at the equator of the cell and spindle fibres attach to centromeres of chromosomes

  
• Anaphase


  spindle fibres contract, breaking centromeres and pulling sister chromatids to opposite poles of the cell

  
• Telophase


  chromatids are at opposite poles of the cell, they uncoil and become long and thin again, called chromosomes

  Nuclear envelope reforms, now 2 nuclei are visible

  
• Cytokinesis

  Cytoplasm divides and 2 genetically identical daughter cells are formed

  
• equation for mitotic index

  number of cells in mitosis/total number of cells x 100
• binary fission


  process by which prokaryotic organisms divide and reproduce
• Conditions for binary fission

  warmth

  moisture

  glucose availability

  oxygen availability
• Process of binary fission

  1- DNA loop and plasmids replicate

  2-cell grows and elongates

  3-DNA loops separate and move to opposite poles of the cell

  4-plasmids randomly distributed throughout cell

  5-murein cell wall and cell membrane forms

  6-cytoplasm divides
• Why doesn't binary fission produce genetically identical daughter cells?

  As the daughter cells have varying numbers of plasmids