Lecture 9: The cytoskeleton 1 Flashcards

1
Q

What is the structure of microtubules?

A

Cylinders 25nm diameter
Made from tubulin heterodimers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are stable dimers as part of microtubules?

A

Alpha and beta tubulin form a stable dimer when they are synthesised
Unseparable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the features of the plus end of microtubules?

A

Grows quickly
B tubulin is exposed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the features of the minus end of microtubules?

A

Grows slowly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is nucleation in microtubules?

A

Tubulin concentration is too low for polymerisation to be spontaneous
Cells use a template of gamma tubulin to speed up polymerisation
This is nucleation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the orientation of microtubules within the cell?

A

Plus ends are at the perimeter of cell
Minus ends are at the centre

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Why are microtubules considered dynamic?

A

Each one grows and shrinks independently of the others
They can switch between growing and shrinking which is dynamic instability

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the role of GTP and ATP binding in microtubules?

A

Can control the shape activity and function of proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is tubulins role as a GTPase?

A

GDP tubulin cannot polymerise
GDP is exchanged for GTP
GTP tubulin can now polymerise

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the role of the GTP cap in microtubules?

A

If the cap is present the microtubule continues growing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What happens if the GTP cap is lost on a microtubule?

A

The microtubule will depolymerise
If a new cap forms it continues growing again

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Why do GTP microtubules grow and GDP shrink

A

GTP is more tightly bound therefore more stable than GDP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How are growing tubules marked?

A

Protein EB1 binds preferentially to GTP tubulin
GTP tubulin is growing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How does stabilisation occur from tubulin dimers to microtubules?

A

Binding of microtubule-associated proteins along the microtubule OR binding of taxol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are two ways in which microtubules can be depolymerised experimentally?

A

By putting cells on ice
Using drugs that prevent assembly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How does putting cells on ice depolymerise microtubules?

A

Microtubules can depolymerise but not grow

17
Q

How does using drugs depolymerise microtubules?

A

Nocodazole binds dimers and stops them assembling
Colcemid and colchicine bind to ends of microtubules and stop further assembly

18
Q

What are the two subunits of microtubules?

A

Alpha and beta tubulin dimers

19
Q

What do the subunits of microtubules bind?

20
Q

What is the structure of the filament in microtubules?

A

A hollow rigid tube of 25nm

21
Q

What is the stabilising and destabilising drugs of microtubules?

A

Taxol is stabilising
Nocodazole is destabilising

22
Q

What are the motor proteins of microtubules?

A

Dyneins
Kinesins

23
Q

What is the structure of actin filaments?

A

Made from monomeric actin
Thin flexible helical filaments

24
Q

What is the role of actin filaments with ATP?

A

They hydrolyse ATP after assembly because actin is in ATPase

25
What is the role of capping proteins on actin filaments?
The bind to the minus end of actin filaments and prevent depolymerisation
26
What is the difference between actin filament and microtubule polymerisation?
Disassembly happens from different ends Actin polymerisation is altered by natural small molecules
27
What are some natural small molecules that alter actin polymerisation?
Phalloidin stabilises actin filaments Cytochalasin caps filament ends and stops actin polymerisation Latrunculin binds to actin monomers and prevents actin polymerisation
28
Why is only 50% of actin polymerised in the cell compared to 100% in a test tube?
Nucleating proteins promote polymerisation In the cell they are used to control where polymerisation happens and maintain a balance between polymer and monomer
29
What are the subunits of actin filaments?
Actin
30
What do the actin filaments subunits bind?
ATP
31
What are some features of the actin filament?
2 stranded flexible helix 7nm diameter
32
What are the stabilising and destabilising drugs of the actin filaments?
Phalloidin is stabilising Cytochalasin and Latrunculin are destabilising
33
What are the motor proteins of actin filaments?
Myosins