Th1L06 Microtubules

structure
1. composed of micro-tubule-associated proteins (MAPs)
  1. Tubulin is the monomer of microtubules
    1. consists of one molecule or alpha and beta-tubulin
      1. Alpha tubulin, positive end
      2. Beta-tubulin, negative end
  2. Assembly and disassembly of the microtubule
    1. similar to the assembly of actin filaments
    2. GTP bound monomers (alpha-tubulin) assemble onto microtubule
    3. GDP bound beta-tubulin monomers dissociate rapidly
2. long, relatively stiff hollow tubes
  1. thirteen columns of tubulin polymer
3. approximately 25nm
4. can be rapidly disassembled and reassembled
  1. polar and highly dynamic
visible using EM or light microscopy
Functions
1. polymerised in centrosomes
  1. minus end remains close the centrosome and the plus end points outward towards the cell periphery
2. Stabilise the shape of platelets and axons
  1. protrusions are activated by cuts and formed by microfilaments allowing them to adhere to one another and form a clot
3. Anchoring
  1. organise the ER of a cell
4. Cell motility
  1. Cilia and flagella
    1. E.g. in respiratory epithelium
    2. Shows 9:2 structure
    3. Microtubules slide along one another causing the cilium to bend via processive motor proteins
      1. Dyenin
        minus-ended microtubule associated motor protein near nucleus
      2. Kinesin
        moves towards (+) ends (cell periphery)
        Stays attached to the microtubule throughout the ATP hydrolysis cycle (unlike mysosin)
  2. Involved in separation of chromosomes during cell division
    1. Colchicine, vinblastine and taxol
      1. anti-cancer therapeutics
      2. inhibit the function of the mitotic spindle and thus cell division
        Colchicine and vinblastine destabilise microtubules
        Taxol stabilises microtubules
        inhibits microtubule polymerization by binding to tubulin
  3. involved in the movement of organelles, e.g. synaptic vesicles along axons to synapses
    1. Composed of heavy chain (binds to microtubule) and light chain (binds to what needs to be moved)
    2. Vesicles move about 10cm/day which take more than a week down an entire axon

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Th1L06 Microtubules

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	Created by Emma Allde over 8 years ago

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