Lecture 5

Question 1

What is the function of the cytoskeleton?

Answer 1

It allows movement, organization, and gives shape to the cell and organelles

Question 2

What are the three filament types in the cytoskeleton?

Answer 2

Microfilaments, intermediate filaments, and microtubules

Question 3

What are some subcellular structures that microfilaments organize into?

Answer 3

Microvilli, cell cortex, adherens belts, stress fibres, and contractile rings

Question 4

What are microfilaments made of?

Answer 4

Actin monomers

Question 5

What are the two states of actin?

Answer 5

G-actin (globular) and F-actin (filaments)

Question 6

What occurs at the (-) end and the (+) end of an actin filament?

Answer 6

Depolymerization occurs at the (-) end and polymerization occurs at the (+) end

Question 7

What does ATP bound actin favor?

Answer 7

Polymerization

Question 8

What is the rate limiting step of actin polymerization?

Answer 8

Nucleation

Question 9

What is a steady state?

Answer 9

When polymerization = depolymerization due to the concentrations of G-actin and F-actin being at equilibrium

Question 10

How does the treadmilling of microfilaments generate force in the cell?

Answer 10

Treadmilling means that the microfilament is not changing in length, but it is moving in one direction. This movement is what generates the force.

Question 11

What are actin sequestering proteins?

Answer 11

Proteins that bind at actin to prevent spontaneous polymerization.

Question 12

What is profilin?

Answer 12

It enhances the loss of ADP off G-actin to increase the concentration of ATP-G actin

Question 13

What is cofilin?

Answer 13

It binds to ADP-F actin and increases destabilization

Question 14

What are myosins?

Answer 14

Myosins are ATP dependant proteins that can bind actin, undergo a conformational change, and move against the rigid actin CSK

Question 15

What do all myosins contain?

Answer 15

An actin binding head domain, a flexible neck, and a tail domain

Question 16

What does a myosin head domain bind to?

Answer 16

Actin and ATP

Question 17

What does a myosin tail domain bind to?

Answer 17

Cargo

Question 18

Where are microtubules anchored?

Answer 18

MTOC (centriole)

Question 19

Which end of the microtubule anchors in the MTOC?

Answer 19

The negative end

Question 20

Where are the positive ends of microtubules found?

Answer 20

Near the edges of the cell

Question 21

What is Gamma-TURC?

Answer 21

It is the nucleation site for microtubules

Question 22

How do microtubules facilitate CSK-based movement?

Answer 22

By constantly assembling and dissassembling themselves to generate force in a particular direction

Question 23

Which has a greater role in cellular movement: microtubules or microfilaments?

Answer 23

The treadmilling of microtubules

Question 24

What does catastrophe refer to?

Answer 24

The rapid disassembly of microtubules when GTPase activity catches up with the polymerization

Question 25

What are the two motors that are associated with microtubules?

Answer 25

Kinesins and dyneins

Question 26

What is the major difference between kinesin and dynein?

Answer 26

Kinesin is a (+) end directed motor and dynein is a (-) end directed motor

Question 27

How do kinesins move?

Answer 27

Via hand-over-hand movement

Question 28

How do dyneins move?

Answer 28

A power stroke that involves the rotation around the head domain

Question 29

What is the function of intermediate filaments in the nuclear lamina?

Answer 29

It forms a meshwork on the inner surface of the nuclear envelope that provides structural support to the nucleus