Cytoskeleton

Question 1

How long in diameter is each component of the cytoskeleton?

Answer 1

MT-20nm
MF- 7nm
IF - 10nm

Question 2

What are the filaments of individual actin proteins made up of?

Answer 2

G-actin

Question 3

How many actin subunits are there for a complete turn of the helix?

Answer 3

13

Question 4

What is the shape of an actin filament?

Answer 4

Polarised double helix

Question 5

How many nm is the length of a complete turn of the actin filament?

Answer 5

37nm

Question 6

What does the asymmetric shape of the actin monomer lead to?

Answer 6

The polarity of the filament

Question 7

Explain how the growth of the actin filament occurs?

Answer 7

Monomers are added to the filament with the use of ATP. Monomers are added more rapidly to the positive end. The ATP is hydrolysed in ADP.

Question 8

What are the major functions of actin? (3)

Answer 8

• Mechanical support
• Cell shape and maintenance
• Cell motility

Question 9

What can we add to G-actin monomers to stop it polymerising?

Answer 9

proteins

Question 10

Where are IF most dense?

Answer 10

Around the nucleus

Question 11

What is the main role of IF?

Answer 11

Mainly mechanical structure, used to anchor cells are some cell junctions. it supports nuclear structure and protects chromatin.

Question 12

What are specialised intermediate filaments called and what do they do?

Answer 12

Lamins and they support nuclear structure and protect chromatin.

Question 13

Explain the 4 step formation of the intermediate filament polymer?

Answer 13

1. Intermediate filament polymer (monomer) held end to end
2. This forms a helical dimer
3. Two dimers combine to form a tetramer
4. Tetramers link in a staggered formation and end-to-end to form the filament

Question 14

Explain the structure of a microtubule and its subunits

Answer 14

The polymer is built from monomers of tubulin. There are 13 monomers in the cross-section. Tubulin monomers consist of an alpha tubular and one beta tubulin.

Question 15

In the assembly of a microtubule, what energy releasing molecule is used?

Answer 15

GTP

Question 16

What are the main 4 functions of the cytoskeleton?

Answer 16

1 = cell shape and polarity (actin filaments provide support)
2 = Cell shape and orientation (IF and MT stabilising the axon in nerve cells)
3 = Anchoring organelles (MT organise the endoplasmic reticulum of a cell and IF form a meshwork around the nucleus to hold it in place 
4 = Cell motility (Actin - based movements essential to anchor cells to each other and to extracellular matrix at cell junctions.

Question 17

What are the 4 steps for actin - based cell movement?

Answer 17

1. Cell pushes out protrusions at the front and the actin filament polymerisation provides the force for membrane protrusion. Addition of monomers towards the cell periphery
2. The protrusions adhere to the surface on which the call id moving through focal adhesion (collection of molecules which attach to another substance). F-actin connects to the focal adhesions to provide a contractile force for the cell.
3. The rest of the cells pulls against the anchorage points to drag itself forward.
4. Actin depolymerises at the rear

Question 18

Why does the actin sample the environment?

Answer 18

So that it can extend and withdraw, generated by rapid growth of actin filaments at the cell membrane.

Question 19

How do muscles generate a contractile force?

Answer 19

• Actin filaments are pulled along by myosin
• The head of the myosin interacts with actin and bind ATP. Energy release from ATP hydrolysis forces the myosin tail to move
• ADP is released from the myosin head and replaced by ATP. The head then detaches from the actin filament.
• The head can then bnd further down the filament to generate a force there

Question 20

What 2 motor proteins move vesicles along microtubules?

Answer 20

Kinesin and Dynein