Mammalian cell biology 6

• what are microtubules made from

  alpha and beta tubulin
• what modifies microtubule organisation and function

  microtubule binding proteins
• what do microtubule associated proteins (MAPS) do

  stabilise the tracks in bundling microtubules
• what do plus end binding proteins do

  • control the dynamics of microtubules and participate in intracellular motility
  • attachment of microtubules to the cell periphery
  • control of microtubule dynamic behaviour
  • control of intracellular trafficking by regulating dynein
• microtubule organising centre

  • microtubules are nucleated at the centrosome
  • from a microtubule organising centre near the nucleus
  • the centrosome consists of the centrioles and the peri-centriolar material (PCM)
  • the PCM contains gamma-tubulin which nucleates the microtubules
• centrioles

  • centrioles consist mainly of microtubule
  • centrioles become the basal body of flagella and cilia
  • centrioles organise the PCM and ensure its inheritance
  • fungi and plants do not have centrioles (but use gamma-tubulin for microtubule nucleation)
• what is a catastrophe

  the switching from assembly to disassembly
• what is a rescue

  the switching from disassembly to assembly
• how is tubulin added and released at one end of the polymer

  1. polymerisation
  2. pausing
  3. depolymerisation
  4. polymerisation
• 1. polymerisation

  • beta-tubulin is a GTPase
  • GFP-tubulin + H2O → GDP-tubulin + phosphate
  • GTP-bound tubulin dimers get added to the plus end
  • a cap of GTP-tubulin stabilises the growing microtubule
• 2. pausing

  • when the amount of available GTP-tubulin dimers is too low the process pauses and hydrolysis removes the GTP-cap
  • tubulin hydrolyses the bound GTP while the microtubule polymerises
• 3. depolymerisation

  • without the GTP-cap the microtubule becomes unstable and depolymerises
  • the moment of transition is called a catastrophe
• 4. polymerisation

  • GTP-tubulin can bind the shrinking microtubule and establish a new cap
  • the moment of transition is called a rescue event
  • microtubules constantly switch between growth and shrinkage (dynamic instability)
• what is f-actin formed from

  G-actin that assembles into nucleation seeds