microfilaments, microtubules and intermediate filaments Flashcards
what is the structure of a microtubule?
13 protofilaments, each polymers of aB-tubulin, which assemble into a hollow tube.
(-) end has an a-subunit exposed, (+) end has B-subunit exposed
what is the difference between the a and B subunits of the tubulin dimer?
a- subunit binds a trapped and non-hydrolysable GTP
B-subunit binds an exchangeable and hydrolysable GTP
what is the centrosome?
the microtubule organising centre that nucleates the radial array of microtubules in a non-mitotic cell
how do microtubules in a neuronal axon differ from other animal cells?
they are non-continuous
what are basal bodies?
MTOC of cilia and flagella
what is the role of the gamma tubulin ring complexes?
act as a template for microtubule nucleation and allow them to grow outwards
how is GTP hydrolysis involved in microtubule dynamics?
GTP hydrolysis changes the conformation of the subunits and weakens bonds in the polymer (cause catastrophe)
how is microtubule dynamics regulated?
the + end has a GTP B-tubulin cap, which keeps the microtubule straight and rigid, when the cap is hydrolysed, the protofilaments disassemble due to reduced stability of GDP
what are the roles of MAPs?
- stabilise fillaments (growth)
- destabilise filaments (catastrophe)
- link filaments to other molecules or structures
how do we know the (+) end of a microtubule is responsible for dynamics?
in vivo, the minus end is anchored and protected at the centrosome
what is the role of kinesin-13?
destabilises microtubule ends to enhance the frequency of catastrophes
what are kinesins and how do they work?
(+) directed, ATP dependent motor proteins. transport organelles
how does kinesin-1 move?
consists of two heavy chains, each with N-terminal motor domain and two light chains that associate with cargo. conformational change upon ATP hydrolysis positions one head domain in front of the other
why is kinesin-1 highly processive?
it coordinates ATP hydrolysis between its two heads so that one head is always firmly bound to a microtubule
what are dyneins and how do they work?
minus end directed motor proteins, utilise a dynactin complex to link motor to cargo. utilise adaptor proteins to bind a variety of cargoes.