cytoskeleton

• microfilaments

  thin, flexible, give mechanical support, and can change shape of a membrane for muscle contraction
• microfilament size

  7nm
• microfilaments change length by rapid polymemerisation and depolymerisation of actin subunits
• when actin subunit is bound to ATP, it has a higher affinity for the filament, the longer it is bound the higher the likelyhood of ATP hydralising to from ADP
• monomers are incorporated into filament via non covalent interactions
• actin regulates microfilament dynamics (stop or facilitate polymerisation)
• actin forms a track fro the myosin protein to form contractile structures
• microtubules

  made from tubulin, long hollow cylinders
• microtubule action

  form cell division spindle, transport tracks for kinesin and dynein, power flagella and cilia
• microtubule size

  25nm and less flexible
• how do microtubules constantly change length

  rapid polymerisation and depolymerisation of tubulin subunits
• when a microtubule is no longer needed, it can be removed and subunits reassemble elsewhere
• how is a GDP cap formed

  polymer assembles quickly, meaning a new subunit will be added before hydrolisation
• if something slows formation of microtubule, formation of GDP from GTP occurs more quickly and results in disassembly
• MTOC action

  anchors minus end of microtubules
• intermediate filament

  stable to provide strength and support
• intermediate filament size

  10nm
• intermediate filament composition

  fibrous proteins
• myosin action

  travels along microfilaments for cell movement and contraction
• dynein action

  travels towards negative end of microtubules for vesicle transport, also beating of flagella and cilia
• kinesin action

  travel towards positive end of microtubules for vesicle and organelle transport
• 3 motor proteins

  myosin, dynein, kinesin
• bundles of myosin forms muscle thick filaments
• actin thin filaments slide past thick filaments to contract muscle
• sacomere shortens from contraction of myosin, contracting muscle
• tropomyosin action at rest

  blocks access to myosin binding sites on actin
• calcium action in contraction

  nerve imulses release calcium, that binds to toponin, complex then exposes myosin binding sites for contraction
• dynein in flagella nad cilia

  dynein moves along microtubules to power movement
• microfilament distribution is concentrated beneath the plasma membrane
• microfilaments form:

  microvilli, cytoplasmic contractile bundles, lamellipodia, filipodia, cell division contractile ring
• actin molecules are joined by non-covalent bonds
• microfilaments can have proteins bound to them to make them more stable
• beta tubulin is always exposed at the positive end
• MTOC is found at the base of flagella and cilia, as well as anchoring microtubules
• centrosome is the starting point for tubular formation
• cycles of conformational change produce movement of myosin head along actin filament