Lecture 10 - Microtubules and Intermediate Filaments

Question 1

What are microtubules and what do they do

Answer 1

‘Bones’ of the cell (or poles in a tent)

Resist compressive force – more rigid than actin filaments

Largest of cytoskeleton polymers: 25 nm wide

Dynamic structural elements

Mitosis and meiosis – ensure separation of chromosomes

Tracks for vesicle trafficking

Cilia and flagella

Question 2

Describe the structure of Microtubules

Answer 2

Repeating unit = ab dimers

Both bind GTP but only b-tubulin hydrolyses to GDP

Microtubules are polar: + and - ends

Heterodimers assemble lengthwise αβ αβ αβ αβ

13 protofilaments of heterodimers

Lateral associations between α-α and β- β, slightly staggered (spiralling tube)

Question 3

How does GTP hydrolysis determine Microtubule dynamics (Slide 6)

Answer 3

Molecular association stronger when b-tubulin is bound to GTP

ab heterodimers assemble at + end

GTP hydrolysis more likely to occur in polymerised b-tubulin

Conformational change that curves filament and weakens bonds between subunits  depolymerisation at + end

Question 4

What is the use of the GTP cap

Answer 4

Stabilises growing Microtubules

(if date of addition > rate of GTP hydrolysis, MT will continue to grow)

Question 5

How does microtubule rapid disassembly occur

Answer 5

GTP hydrolysis catches up, rapid shrinking from + end (slide 8+9)
Helps regulation (growth and collapse (catastrophe))

Question 6

What is the MTOC

Answer 6

microtubule organising centre

Question 7

How are new Microtubules formed

Answer 7

gamma-tubulin: forms ring-shaped scaffold for addition of alpha,beta dimers

Nucleate (start) from the MTOC or existing MTs

Question 8

What is a centrosome

Answer 8

Large aggregation of MT nucleating complexes typically found near nucleus

Question 9

How do Microtubules drive separation of chromosomes

Answer 9

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Question 10

How do microtubule dynamics guide cell movement

Answer 10

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Question 11

Microtubule dynamics

Answer 11

Add

Question 12

What are kinesins

Answer 12

Plus end directed microtubule motors

Question 13

What are Dyneins

Answer 13

Minus end directed microtubule motors

Question 14

Anterograde and retrograde

Answer 14

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Question 15

Cargo-bindinh tail domains in dyneins and kiniens

Answer 15

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Question 16

Cilia and flagell

Answer 16

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Question 17

What are intermediate filaments and what do they do

Answer 17

‘Ligaments’ of the cell (webbing)

Rope-like fibers – tough and inelastic

Intermediate width ~ 10 nm

Non-polar (unlike actin and MTs)

Diverse family (unlike actin and MTs)

Different types expressed in different cells and tissues

Question 18

slide 25 onwards —-