Intro to the Cytoskeleton

Question 1

How many strands make up an intermediate filament?

Answer 1

32

Question 2

What are the 3 components of the cytoskeleton?

Question 3

What are the properties of intermediate filaments?

Answer 3

• Very strong
• Very stable
• Very insoluble

Question 4

Outline the structure of intermediate filaments

Answer 4

• Dimers form as head to head coiled structures
• Tetramers form head-to-tail and assemble into rope-like filaments

Question 5

Describe the structure of intermediate filament proteins

Answer 5

Elongated with a central α helical region

Question 6

What is a dermasome?

Answer 6

Connections between epithelial cells

Question 7

What is a hemidesmasome?

Answer 7

Connects cells to underlying extracellular matrix

Question 8

How do intermediate filaments like keratin support epithelial cells?

Answer 8

• Span epithelial cells forming a framework that supports the cell and links it mechanically to its framework
• Supports the cell and links it mechanically to its neighbours
• Mechanically couples cells together so force is spread out along whole skin layer

Question 9

What causes Epidermolysis Bullosa Simplex?

Answer 9

Defects in keratin

Question 10

What happens in Epidermolysis Bullosa Simplex?

Answer 10

Produces weak intermediate fibres so if force is apploed it is not spread out so cells burst and blistering of the skin occurs

Question 11

What is the basic subunit of actin?

Answer 11

G (globular) actin

Question 12

What is bound centrally in actin?

Answer 12

ATP/ADP

Question 13

What is the polymer of actin?

Answer 13

F (filamentous) actin

Question 14

What is the structure of filamentous actin?

Answer 14

A right handed helix made up of two protofilaments

Question 15

Is F actin symmetrical?

Answer 15

No, it is asymmetrical

Question 16

How does growth of actin occur?

Answer 16

By the addition of actin monomers to the plus end

Question 17

What is the 1st stage of actin polymerisation?

Answer 17

Nucleation, formation of the trimer

Question 18

What is the rate limiting step in actin polymerisation?

Answer 18

Formation of the trimer

Question 19

What is Cc?

Answer 19

The critical concentration of G actin, where rates of addition and loss are balanced and there is no net polymerisation

Question 20

What happens to intermediate filaments at Cc?

Answer 20

The filaments are neither growing or shrinking

Question 21

Where is most actin bound to ATP?

Answer 21

At the plus end

Question 22

Why is most actin ADP bound at the negative end?

Answer 22

As the filament gets older there is spontaneous ATP hydrolysis

Question 23

At a steady state where is actin preferentially lost

Question 24

is k_off higher for ATP or ADP actin?

Answer 24

ADP-actin

Question 25

What allows an actin filament to stay the same length but constantly be turning over?

Answer 25

2 different rates of depolymerisation at different rates

Question 26

What is used to visualise the actin cytoskeleton?

Answer 26

Phalloidin

Question 27

How does phalloidin help to visualise the actin cytoskeleton?

Answer 27

It binds to F-actin and stabilises filaments

Question 28

What joins actin together to produce a mesh?

Answer 28

Filamin

Question 29

Outline the structure of filamin

Answer 29

* It is a dimer * Each subunit has an actin binding site

Question 30

How does the actin cytoskeleton give the cell strength?

Answer 30

* Actin cytoskeleton form a cortical cytoskeleton beneath the plasma membrane * Anchored by transmembrane proteins * Allows force to be spread across the plasma membrane of the whole cell

Question 31

Give the role of actin filaments in red blood cells

Answer 31

Actin filaments form a network with spectrin filaments to support the rbc shape

Question 32

How do actin filaments drive membrane protrusion?

Answer 32

Actin filaments are cross-linked to form bundles in order to make them more rigid so the actin can push against the membrane with sufficient force

Question 33

What are filopodia?

Answer 33

Cytoplasmic projections which sense rhe surroundingof the cell and look for chemotoxic signals

Question 34

What are lamellipodia?

Answer 34

Cytoskeletal actin projections on the leading edge of the cell, which are used when the cell wants to move

Question 35

Outline the structure of myosin

Answer 35

2 heavy chains intertwined to form a long coiled rail region with two globular heads

Question 36

What is linked to mechanical movement of the myosin head domain?

Answer 36

ATP hydrolysis

Question 37

What is the basic subunit of microtubules?

Answer 37

αβ tubulin dimer

Question 38

What is bound at the centre of each tubulin dimer?

Answer 38

GDP/GTP

Question 39

Are microtubules symmetric?

Answer 39

No they are asymmetric

Question 40

Outline the structure of microtubules

Answer 40

* Right handed helical tube of protofilaments * Hollow in the centre with a cross section of 13 subunits

Question 41

How does growth of a microtubule occur?

Answer 41

By the addition of tubulin dimers to the plus end

Question 42

What is the primary function of microtubules?

Answer 42

Form a railway network within the cell

Question 43

What stabilises the growing tip of microtubules?

Answer 43

GTP-bound β subunits, this is called a GTP cap

Question 44

Can the GTP on the α tubulin subunit be hydrolysed?

Answer 44

No

Question 45

Can the GTP on the β tubulin subunit be hydrolysed?

Answer 45

Yes, it spontaneously hydrolyses to GDP

Question 46

What is the effect of the loss of the GTP cap on microtubules?

Answer 46

It causes catastrophe, the microtubule to depolymerise

Question 47

Why does loss of the GTP cap in microtubules lead to catastrophe?

Answer 47

GDP bound β subunits have a different conformation which induces a curve in the protofilament, this destabilises the microtubule

Question 48

What anchors microtubules?

Answer 48

The centrosome

Question 49

Where is the centrosome located in most cell types?

Answer 49

Near the nucleus

Question 50

Which end of a microtubule is tethered to the centrosome?

Answer 50

The minus end

Question 51

What protein is the centrosome rich in?

Answer 51

γ-TuRC

Question 52

Outline the structure of the centrosome

Answer 52

* in the centre 2 centrioles at right angles to each other * Matrix contains rings of γ-tubulin which nucleate the growth of new microtubules

Question 53

Where is γ-tubulin found?

Answer 53

Only in the centrosome

Question 54

What are centrioles?

Answer 54

Central short microtubues with accessory pigments

Question 55

How does γ-tubulin nucleate the growth of new microtubules?

Answer 55

γ tubulin forms 1st ring of tubulin, αβ dimers can then join on

Question 56

What are the 2 families of motor proteins that microtubules interact with?

Answer 56

Kinesin and dynein

Question 57

Which direction do kinesins travel?

Answer 57

Towards the plus end of the microtubule

Question 58

What direction do dyneins travel?

Answer 58

Towards the minus end of the microtubule

Question 59

How do motor proteins bind to vesicles and organelles?

Answer 59

Through their tails

Question 60

How do kinesins and dyneins recognise microtubules?

Answer 60

Through their head regions

Question 61

How do motor proteins track along the microtubule?

Answer 61

They hydrolyse ATP in their heads

Question 62

What happens to microtubules at interphase?

Answer 62

Microtubules break down and the centrosome is duplicated

Question 63

What kind of microtubules attach to the chromosome pairs?

Answer 63

Kinetochore microtubules

Question 64

What is the function of astral microtubules?

Answer 64

they help orientate and position the spindle in the centre of the cell so can alter the axes of division

Question 65

What is the role of motor proteins in cell division?

Answer 65

They interact with the spindle to regulate shape and position of the chromosomes

Question 66

How do microtubules ensure they are attached to something during cell division?

Answer 66

Each microtubule will tug on each chromosome