L16- The cytoskeleton 1

Question 1

What are the 3 basic principles of the cytoskeleton?

Answer 1

1. Single proteins (monomers) that assembles into very long polymers via non-covalent interactions between subunits.
2. Polymers can assemble and disassemble.
3. Each class of filament has its own set of associated proteins

Question 2

What are the 3 types of cytoskeleton filaments?

Answer 2

1. Actin filaments
2. Microtubules
3. Intermediate filaments

Question 3

In which organisms are intermediate filaments found?

Answer 3

Found in most animals. Not in unicellular organisms, plants or fungi.

Question 4

Where are intermediate filaments found? in the body

Answer 4

1. Karatin e,g, in hair
2. Vimetin e.g. connective tissue, muscle and glia
3. Neurofilaments - in nerve cells
4. Nuclear lamins- in all nucleated cells (ie not RBCs)

Question 5

What can mutations in nuclear lamins lead to?

Answer 5

Diseases including progeria- a premature ageing syndrome

Question 6

What’s the strongest filament?

Answer 6

Intermediate filaments

Question 7

Give 4 properties of intermediate filaments?

Answer 7

1. 10nm in diameter
2. Strong, durable
3. Stable (do not grow and shrink rapidly)
4. Do not bind nucleotides (eg ATP or GTP)

Question 8

How do intermediate filaments strengthen animal cells?

Answer 8

They give protection against stretching. They can link in adjacent cells via desmosomes.

Question 9

What happens if keratin is mutated?

Answer 9

The skin is weak. Causes skin blistering diseases

Question 10

What strengthens neurones which may have axons over 1m long?

Answer 10

Neurofilaments- a type of intermediate filament

Question 11

Describe the structure of intermediate filaments?

Answer 11

There’s an alpha helical monomer.Then 2 monomers which are parallel (all NH and COOH ends on the same sides) coil together to form a dimer. Tetramer of 2 antiparallel dimers (staggered). Then 8 tetramers come together to make a filament!
So 32 of the alpha helical monomers all together.

Question 12

What does each type of filament bind to?

Answer 12

1. Actin-> ATP
2. Mictroubules-> GTP
3. Intermediate -> NOTHING!

Question 13

What subunits make up each type of filament?

Answer 13

1. Actin-> Actin
2. Mictrobules-> alpha/beta tubulin dimers
3. Intermediate -> various

Question 14

Describe the filament structure of each type of filament?

Answer 14

1. Actin-> 2-stranded flexible helix
2. Mictrobulues -> Hollow tube, fairly rigid
3. Intermediate-> 8-stranded flexible helix

Question 15

What’s the diameter of each filament?

Answer 15

1. Actin- 7nm
2. Mictrobulues- 25 nm
3. Intermediate- 10nm

Question 16

Which drugs stabilise each type of filament?

Answer 16

1. Actin- Phalloidin
2. Microtubules- Taxol
3. Intermediate- none

Question 17

Which drugs destabilise each type of filament?

Answer 17

1. Actin- Cytochalasin, latrunaulin
2. Microtubules- Nocodazole
3. Intermediate- none

Question 18

What motor proteins are there in each type of filament?

Answer 18

1. actin- myosin
2. Mictroubules- dyneins and kinesins
3. Intermediate- none

Question 19

Describe the main structure of microtubules?

Answer 19

Hollow, unbranched cylinders of 25 nm diameter

Question 20

Describe the polarity of microtubules?

Answer 20

They have + and - ends. + end grows and shrinks. - end grows slowly, if at all.

Question 21

What is exposed at the plus ends of microtubules?

Answer 21

Beta- tubulin