The Importance of Mitosis & Apoptosis (OCR A Level Biology): Revision Note

The Importance of Mitosis & Apoptosis

• Mitosis and apoptosis play an essential role in the correct development of organisms

  • Mitosis = cell division that produces identical new cells for growth, cell replacement and tissue repair

  • Apoptosis = programmed cell death during which:

    1. enzymes digest cell contents

    2. the cell breaks apart into small fragments

    3. phagocytes engulf any remains

• By constantly producing and destroying cells throughout the early development of an organism, mitosis and apoptosis control the development of body form

  • Mitosis occurs in regions where more cells are needed

  • Apoptosis occurs in regions where cells need to be removed

    • E.g. structures like fingers and toes first develop as a single combined unit and are then separated later by removal of the cells in between the digits

    • Note that apoptosis also plays an essential role in destroying infected, damaged or old body cells

The control of mitosis and apoptosis

• The cell cycle is controlled by various genes, e.g.:

  • proto-oncogenes stimulate cell division

  • tumour-suppressor genes reduce cell division

    • Tumour-suppressor genes can also stimulate apoptosis

• Genes that regulate the cell cycle control progression of the cycle by sensing issues like DNA damage or faulty spindle attachment

  • Progression through the cell cycle is paused at cell checkpoints if issues are detected

  • If issues cannot be repaired then mitosis will be prevented and apoptosis may be triggered

• The genes that control the cell cycle and apoptosis are able to respond to:

  • internal cell stimuli, e.g.:

    • DNA damage that cannot be repaired

    • activation of genes that stimulate cell division

    • metabolic stress, e.g. ATP depletion

  • external cell stimuli, e.g.:

    • cell signalling molecules such as cytokines and hormones

    • the presence of pathogens

    • chemicals in the environment