MCB Lecture 35 Cytoskeleton II Flashcards Preview

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Flashcards in MCB Lecture 35 Cytoskeleton II Deck (37)
0

Describe how myosin causes actin filaments to move

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

1

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

The head cocks and binds to the actin filament

2

What triggers the power stroke?

The dissociation of the phosphate

3

What does ATP binding to myosin trigger?

The dissociation of the myosin head from actin

4

Describe the three stages in cell locomotion

1. Protrusion
2. Adhesion
3. Traction

5

Describe the attachment phase of cell locomotion

New focal contacts are made at the mobile side of the cell
Old focal adhesions at the other side are removed

6

Describe the traction phase of cell locomotion

Focal adhesions produce Cell traction forces
Myosin rearranges the actin, producing stress and contractile forces

7

How are cells guided when they move?

They follow chemical gradients or molecules

8

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

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

9

Describe the formation of Microtubules

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

10

What is the structure of a protofilament of a microtubule?

It is a strand of dimers connected head to tail

11

Describe the polarity of a microtubule protofilament

+/beta end
-/alpha end

12

What are some functions of microtubules? (3)

Form tracts around the cell
Cilia and flagella
Mechanical work

13

What is the function of the GTP-cap?
What happens if it lost?

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

14

Describe polymerisation of microtubule protofilaments

Dimers added to the protofilament on the beta end

15

What is the rate limiting step in microtubule formation?

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

16

Which complex speeds up nucleation of microtubules?

Gamma-Tubulin ring complex

17

Which organelle produces microtubules?
Describe its structure

Centrosome
It is a sphere with two centrioles

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

18

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

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

19

Describe the function of MAP

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

20

... microtubule forms tracks around the cell

Stabilised

21

Which motor proteins move materials around on the microtubule cytoskeleton?

Kinesin and Dynein

22

Differentiate between Kinesin and Dynein

Kinesin moves stuff anterograde: toward the plus end
Dynein: moves stuff retrograde: towards the minus end

23

Describe how motor proteins generate force

ATP hydrolysis couples with conformational changes

24

How do Kinesin and Dynein interact with the microtubule?

In a similar way that myosin interacts with actin filaments

25

How do Kinesin and Dynein associate with vesicles?

Through many proteins

26

Describe the dynamic instability of microtubules, and how catastrophes occur

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

27

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

The extending end

28

What is important about the dimer that forms microtubule filaments?

It is a heterodimer: alpha and beta subunit

29

What is the structure of a microtubule?

13 protofilaments

30

What is the structure of microtubules in cilia and flagella?

9 + 2

31

Wat is meant by the dynamic instability of microtubules?

They undergo phases of rapid polymerisation as well as rapid depolymerisation

32

What can lead to decreased stability of the GTP cap?

Hydrolysis of the GTP to GDP

33

What are the three types of Tubulin monomers?

Alpha, beta, gamma

34

How do we control where we want to synthesis microtubule?

The controsome can be moved around the cell

35

How can microtubules be destabilised?

Binding of certain proteins to the GTP Cap

36

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

Vesicles travel along microtubule

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