Th1L06 Microtubules

Th1L06 Microtubules

1. structure

   • composed of micro-tubule-associated proteins (MAPs)
     • Tubulin is the monomer of microtubules
       • consists of one molecule or alpha and beta-tubulin
         • Alpha tubulin, positive end
         • Beta-tubulin, negative end
     • Assembly and disassembly of the microtubule
       • similar to the assembly of actin filaments
       • GTP bound monomers (alpha-tubulin) assemble onto microtubule
       • GDP bound beta-tubulin monomers dissociate rapidly
   • long, relatively stiff hollow tubes
     • thirteen columns of tubulin polymer
   • approximately 25nm
   • can be rapidly disassembled and reassembled
     • polar and highly dynamic

2. visible using EM or light microscopy

3. Functions

   • polymerised in centrosomes
     • minus end remains close the centrosome and the plus end points outward towards the cell periphery
   • Stabilise the shape of platelets and axons
     • protrusions are activated by cuts and formed by microfilaments allowing them to adhere to one another and form a clot
   • Anchoring
     • organise the ER of a cell
   • Cell motility
     • Cilia and flagella
       • E.g. in respiratory epithelium
       • Shows 9:2 structure
       • Microtubules slide along one another causing the cilium to bend via processive motor proteins
         • Dyenin
           • minus-ended microtubule associated motor protein near nucleus
         • Kinesin
           • moves towards (+) ends (cell periphery)
           • Stays attached to the microtubule throughout the ATP hydrolysis cycle (unlike mysosin)
     • Involved in separation of chromosomes during cell division
       • Colchicine, vinblastine and taxol
         • anti-cancer therapeutics
         • 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
     • involved in the movement of organelles, e.g. synaptic vesicles along axons to synapses
       • Composed of heavy chain (binds to microtubule) and light chain (binds to what needs to be moved)
       • Vesicles move about 10cm/day which take more than a week down an entire axon

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