Cytoskeleton Flashcards
What is the centrosome?
- Microtubule organising centre
- Made of 2 centrioles
- Positive end of microtubles extend outwards, - end bound to the centrosome
What is y-tubulin?
- Holds the microtubules
- Where nucleation of microtubules occurs
What is the structure of microtubules?
- Many tubulin dimers make a protofilament, with a fast growing barbed + end and a slow growing, pointed - end
- 13 protofillaments make a hollow microtubule
What do microtubules do?
- Control cell shape and therefore cell role
- Important in cell movement of organelles and as a whole cell (form tracts)
- Form the mitotic spindle
How do microtubules assemble?
Spontaneously if concentration of tubulin is high enough
What is the structure of tubulin?
- Dimer of A and B monomers
- Both dimers can bind GTP
- BUT B can also bind GDP
When does catastrophe happen during making microtubules?
- When the rate of subunits being added to the + end is slower than the rate of hydrolysis
- B subunit at the end loses its GTP cap
- Microtubule falls apart
How do actin filaments remain the same length?
- Treadmilling affect
- Subunits added at the + end and dropped at the - end
How is the dynamic stability in microfillaments different to that in microtubules?
In microfillaments there is no cap, polymerisation can taken place at both ends
- But as in microtubules, there is a fast growing + end
Why is theres a lag phase in the assembly of microfillaments?
- There is a ‘critical concentration’ where trimer nucleation can occur
- Trimer nucleation is unenergetically favourable
What are microfillaments involved in?
- Muscle contraction
- Cell strength and shape
- Cell movement
What is the assembly of intermediate fillaments?
- Coiled-coil dimers
- Dimers line up anti-parallel to make tetramers
What are the 2 microtubule motors?
Dynein and kinesin
Describe dynein
- Negative end directed (reterograde transport)
- Bind indirectly to organelles via the dynactin complex
What is the difference between the two types of dynein?
Ciliary - 3 heads
Cytoplasmic - 2 heads
Describe kinesin
- Positive end directed (anterograde transport)
- Has a conserved motor domain which binds to microtubules
- Has a variable tail which binds directly to specific cargo
