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From Molecules to Cells > Lecture 9: The cytoskeleton 1 > Flashcards

Lecture 9: The cytoskeleton 1 Flashcards

1
Q

What is the structure of microtubules?

A

Cylinders 25nm diameter
Made from tubulin heterodimers

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2
Q

What are stable dimers as part of microtubules?

A

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

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3
Q

What are the features of the plus end of microtubules?

A

Grows quickly
B tubulin is exposed

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4
Q

What are the features of the minus end of microtubules?

A

Grows slowly

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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

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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

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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

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8
Q

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

A

Can control the shape activity and function of proteins

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9
Q

What is tubulins role as a GTPase?

A

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

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10
Q

What is the role of the GTP cap in microtubules?

A

If the cap is present the microtubule continues growing

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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

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12
Q

Why do GTP microtubules grow and GDP shrink

A

GTP is more tightly bound therefore more stable than GDP

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13
Q

How are growing tubules marked?

A

Protein EB1 binds preferentially to GTP tubulin
GTP tubulin is growing

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14
Q

How does stabilisation occur from tubulin dimers to microtubules?

A

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

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15
Q

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

A

By putting cells on ice
Using drugs that prevent assembly

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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?

A

GTP

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
Q

What is the role of capping proteins on actin filaments?

A

The bind to the minus end of actin filaments and prevent depolymerisation

26
Q

What is the difference between actin filament and microtubule polymerisation?

A

Disassembly happens from different ends
Actin polymerisation is altered by natural small molecules

27
Q

What are some natural small molecules that alter actin polymerisation?

A

Phalloidin stabilises actin filaments
Cytochalasin caps filament ends and stops actin polymerisation
Latrunculin binds to actin monomers and prevents actin polymerisation

28
Q

Why is only 50% of actin polymerised in the cell compared to 100% in a test tube?

A

Nucleating proteins promote polymerisation
In the cell they are used to control where polymerisation happens and maintain a balance between polymer and monomer

29
Q

What are the subunits of actin filaments?

A

Actin

30
Q

What do the actin filaments subunits bind?

A

ATP

31
Q

What are some features of the actin filament?

A

2 stranded flexible helix
7nm diameter

32
Q

What are the stabilising and destabilising drugs of the actin filaments?

A

Phalloidin is stabilising
Cytochalasin and Latrunculin are destabilising

33
Q

What are the motor proteins of actin filaments?

A

Myosins

From Molecules to Cells (23 decks)

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