MCB Lecture 35 Cytoskeleton II

Question 0

In muscle contraction, hydrolysis of ATP on the myosin head prompts what?

Answer 0

The head cocks and binds to the actin filament

Question 1

Describe how myosin causes actin filaments to move

Answer 1

1. ATP binds, and the head dissociates from actin
2. ATP is hydrolysed, head cocks and it binds to actin
3. Dissociation of the phosphate triggers the power stroke
4. ADP dissociates during the power stroke

Question 2

What triggers the power stroke?

Answer 2

The dissociation of the phosphate

Question 3

What does ATP binding to myosin trigger?

Answer 3

The dissociation of the myosin head from actin

Question 4

Describe the three stages in cell locomotion

Answer 4

1. Protrusion
2. Adhesion
3. Traction

Question 5

Describe the attachment phase of cell locomotion

Answer 5

New focal contacts are made at the mobile side of the cell

Old focal adhesions at the other side are removed

Question 6

Describe the traction phase of cell locomotion

Answer 6

Focal adhesions produce Cell traction forces

Myosin rearranges the actin, producing stress and contractile forces

Question 7

How are cells guided when they move?

Answer 7

They follow chemical gradients or molecules

Question 8

How do bacteria cells know where to go when they move?

Answer 8

1. Chemoattractants bind to receptors on the surface of bacteria
2. One of two pathways is activated:
   2a. Rac: actin polymerisation
   2b. Rho: myosin activity

Question 9

Describe the formation of Microtubules

Answer 9

Tubulin dimers form
Dimers arrange head to tail to form a protofilament

13 Protofilaments line up side on to form a tube

9 double tubes arranged in a circle, with 2 in the middle form a microtubule

Question 10

What is the structure of a protofilament of a microtubule?

Answer 10

It is a strand of dimers connected head to tail

Question 11

Describe the polarity of a microtubule protofilament

Answer 11

+/beta end

-/alpha end

Question 12

What are some functions of microtubules? (3)

Answer 12

Form tracts around the cell
Cilia and flagella
Mechanical work

Question 13

What is the function of the GTP-cap?

What happens if it lost?

Answer 13

A GTP-cap binds to the beta end and stimulates polymerisation
Without a GTP-cap, catastrophes are much more common and the filament depolymerises

Question 14

Describe polymerisation of microtubule protofilaments

Answer 14

Dimers added to the protofilament on the beta end

Question 15

What is the rate limiting step in microtubule formation?

Answer 15

Nucleation, formation of an oligomer that has enough H bonds to be stable and for polymerisation to then occur

Question 16

Which complex speeds up nucleation of microtubules?

Answer 16

Gamma-Tubulin ring complex

Question 17

Which organelle produces microtubules?

Describe its structure

Answer 17

Centrosome
It is a sphere with two centrioles

The sphere is perforated with gamma-Tubulin Ring Complexes that increase rate of polymerisation

Question 18

What is the function of proteins that bind to micro filaments?

Answer 18

They increase stability, so that the microfilament can form a tract around the cell

Question 19

Describe the function of MAP

Answer 19

MAP binds to the GTP Cap on the plus and reduces the frequency of catastrophes by stabilising the filament

We thus get a longer, more stable filament

Question 20

… microtubule forms tracks around the cell

Answer 20

Stabilised

Question 21

Which motor proteins move materials around on the microtubule cytoskeleton?

Answer 21

Kinesin and Dynein

Question 22

Differentiate between Kinesin and Dynein

Answer 22

Kinesin moves stuff anterograde: toward the plus end

Dynein: moves stuff retrograde: towards the minus end

Question 23

Describe how motor proteins generate force

Answer 23

ATP hydrolysis couples with conformational changes

Question 24

How do Kinesin and Dynein interact with the microtubule?

Answer 24

In a similar way that myosin interacts with actin filaments

Question 25

How do Kinesin and Dynein associate with vesicles?

Answer 25

Through many proteins

Question 26

Describe the dynamic instability of microtubules, and how catastrophes occur

Answer 26

When a GTP-cap is lost, the microfilament rapidly depolymerises.

Question 27

During migration, actin polymerisation preferentially occurs at which end of the cell?

Answer 27

The extending end

Question 28

What is important about the dimer that forms microtubule filaments?

Answer 28

It is a heterodimer: alpha and beta subunit

Question 29

What is the structure of a microtubule?

Answer 29

13 protofilaments

Question 30

What is the structure of microtubules in cilia and flagella?

Answer 30

9 + 2

Question 31

Wat is meant by the dynamic instability of microtubules?

Answer 31

They undergo phases of rapid polymerisation as well as rapid depolymerisation

Question 32

What can lead to decreased stability of the GTP cap?

Answer 32

Hydrolysis of the GTP to GDP

Question 33

What are the three types of Tubulin monomers?

Answer 33

Alpha, beta, gamma

Question 34

How do we control where we want to synthesis microtubule?

Answer 34

The controsome can be moved around the cell

Question 35

How can microtubules be destabilised?

Answer 35

Binding of certain proteins to the GTP Cap

Question 36

What is the role of cytoskeleton in the bio secretory pathway?

Answer 36

Vesicles travel along microtubule