Lecture 14

Question 1

What is the living edge?

Answer 1

The living edge is the component of cells that extends into projections that want to connect and close gaps for example.

Question 2

Two examples of actin binding proteins and their involvements?

Answer 2

a-actinin is rigid, composed of 2 identical subunits (homodimers), and they form contractile or parallel bundles.

filamin is a flexible homodimer and forms a gel-substance

Question 3

What does Arp2/3 do?

Answer 3

Arp2/3 makes branches
- means that cells can push membranes in a certain direction

Question 4

How do actin binding proteins become activated?

Answer 4

Actin binding proteins need a “signal” to become activated

Question 5

What is the signal for the actin binding proteins to be activated?

Answer 5

Rho GTPases are the signal (molecules that hydrolyse GTP)

Question 6

What are the Rho GTPases?

Answer 6

Rho GTPases are Cdc42, Rho, and Rac

Question 7

On and off state of actin binding proteins?

Answer 7

ON = GTP bound
OFF = GDP bound

Question 8

What two enzymes regulate the switch of on to off (GDP to GTP)?

Answer 8

Inactive = GDP, become active through use of a GEF (recruits GTP)

Active = GTP, becomes inactive through use of a GAP (hydrolyzes GTP)

Question 9

Active Rho can do what?

Answer 9

Active Rho can be used for actin remodeling in the cell.

Question 10

What do Rho GTPases signal?

Answer 10

Rho GTPases signal the formation of different actin structures.
- They coordinate the activation of all actin-binding proteins required to build a specific cytoskeletal arrangement

Question 11

Affect of Cdc42?

Answer 11

Cdc42 affects the filopodia, making the cell appear spikier

Question 12

Affect of Rac1?

Answer 12

Rac1 affects the lamellipodia, making the cells push outward more

Question 13

Affect of RhoA?

Answer 13

RhoA affects stress fibres

Question 14

What do Rho family GTPases do?

Answer 14

Rho family GTPases locally activate actin-binding proteins, then they organize the actin filaments.

Question 15

Profilin?

Answer 15

A small protein key regulator of actin polymerization

Question 16

Formins?

Answer 16

A group of proteins that are involved in the polymerization of actin and associate with the fast-growing end of actin filaments.
- grab and add actin to the chain

Question 17

What is present at the leading edge of migrating cells?

Answer 17

Filopodia and lamellipodia are present at the leading edge of migrating cells.

Question 18

What piushed the cell forward?

Answer 18

Actin polymerization and branching pushed the cell forward

Question 19

G-actin incorportation occurs where?

Answer 19

G-actin incorporation occurs at the cell membrane, and it is displaced towards the center of the cell.

Question 20

What do actin-binding proteins organize?

Answer 20

actin binding proteins organize the actin cytoskeleton

Question 21

Transport across microtubules?

Answer 21

Kinesin and Dynein transport things along microtubules

Question 22

Myosins?

Answer 22

Myosins are the motor proteins that walk on actin filaments

Question 23

Compoennts of myosin?

Answer 23

• two heavy chains
• two light chains
• actin binding domains (2)

Question 24

What is the sequence of the myosin power stroke?

Answer 24

1. Without ATP, myosin is attached to the actin filament in rigor
2. ATP binding to the myosin head domain causes the release of actin filament
3. Also caues a large conformational shift in the ‘lever arm’ then ATP is hydrolysed
4. Release of the phosphate
5. The power stroke is the force-generating step
6. ADP is released and the myosin head remains tightly boundd

Question 25

What are members of myosin family?

Answer 25

Actin-based motor proteins are members of the myosin superfamily.

Question 26

Myosin's differ how and are the same how?

Answer 26

All myosin share similar motor domains, but their c-terminal tails are very diverse. - They can be conventional or unconventional

Question 27

Conventional myosins?

Answer 27

II

Question 28

Unconventional myosins?

Answer 28

I, III, V, VI, VII, XI, XIV

Question 29

How do we learn about myosin movement?

Answer 29

Actin sliding assays tell us about how myosin moves actin filaments.

Question 30

How do we know what the motor of myosin is?

Answer 30

If we remove different parts of the chain of myosin, the actin will still move. But if we remove the head of the myosin, the actin will not move- meaning the motor is contained here

Question 31

What are the two types of myosins?

Answer 31

There is conventional and unconventional myosin

Question 32

Conventional myosin forms _____?

Answer 32

Conventional myosin forms bipolar filaments - Myosin II

Question 33

Unconventional myosin forms _______?

Answer 33

Unconventional myosins do not form bipolar filaments - Myosin I, V, VI

Question 34

What is the role of myosin V?

Answer 34

Myosin V tethers and transports organelles - they transport a variety of cargo - they move towards plus ends

Question 35

Components of myosin V?

Answer 35

- GLobular tail binds cargo - dimerization - Ca regulatory region - actin and ATP binding at head

Question 36

What cargo does myosin transport and what direction does it go?

Answer 36

- Myosins transport a variety of cargo - They move towards the plus ends

Question 37

Myosin I?

Answer 37

Myosin I has only one head, binds membrane and powers membrane deformation (no dimer!) - Myosin-I molecular motors are comprised of a motor domain that binds to and interacts with actin in response to ATPase cycling, a light-chain-binding domain (LCBD) that binds one to six Ca2+-sensitive calmodulin or calmodulin-like light chains and functions as a lever arm.