Cytoskeleton

Question 1

What is the centrosome?

Answer 1

• Microtubule organising centre
• Made of 2 centrioles
• Positive end of microtubles extend outwards, - end bound to the centrosome

Question 2

What is y-tubulin?

Answer 2

• Holds the microtubules

- Where nucleation of microtubules occurs

Question 3

What is the structure of microtubules?

Answer 3

• Many tubulin dimers make a protofilament, with a fast growing barbed + end and a slow growing, pointed - end
• 13 protofillaments make a hollow microtubule

Question 4

What do microtubules do?

Answer 4

• Control cell shape and therefore cell role
• Important in cell movement of organelles and as a whole cell (form tracts)
• Form the mitotic spindle

Question 5

How do microtubules assemble?

Answer 5

Spontaneously if concentration of tubulin is high enough

Question 6

What is the structure of tubulin?

Answer 6

• Dimer of A and B monomers
• Both dimers can bind GTP
• BUT B can also bind GDP

Question 7

When does catastrophe happen during making microtubules?

Answer 7

• 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

Question 8

How do actin filaments remain the same length?

Answer 8

• Treadmilling affect

- Subunits added at the + end and dropped at the - end

Question 9

How is the dynamic stability in microfillaments different to that in microtubules?

Answer 9

In microfillaments there is no cap, polymerisation can taken place at both ends
- But as in microtubules, there is a fast growing + end

Question 10

Why is theres a lag phase in the assembly of microfillaments?

Answer 10

• There is a ‘critical concentration’ where trimer nucleation can occur
• Trimer nucleation is unenergetically favourable

Question 11

What are microfillaments involved in?

Answer 11

• Muscle contraction
• Cell strength and shape
• Cell movement

Question 12

What is the assembly of intermediate fillaments?

Answer 12

• Coiled-coil dimers

- Dimers line up anti-parallel to make tetramers

Question 13

What are the 2 microtubule motors?

Answer 13

Dynein and kinesin

Question 14

Describe dynein

Answer 14

• Negative end directed (reterograde transport)

- Bind indirectly to organelles via the dynactin complex

Question 15

What is the difference between the two types of dynein?

Answer 15

Ciliary - 3 heads

Cytoplasmic - 2 heads

Question 16

Describe kinesin

Answer 16

• Positive end directed (anterograde transport)
• Has a conserved motor domain which binds to microtubules
• Has a variable tail which binds directly to specific cargo