lecture 10 - cytoskeleton

Question 1

What are motor proteins?

Answer 1

Use ATP hydrolysis as energy to move along cytoskeleton. Motor proteins that move along actin filaments are called myosins

Myosin can bind and hydrolyze ATP
This provides the energy for their movement along actin filament from the minus end towards the plus end

Question 2

How does the myosin move the actin filaments?

Answer 2

Attached: head lacks ATP and is locked onto the actin filaments
Released: When ATP binds to myosin a conformational change this reduces affinity for the myosin filament
cocked: ATP to ADP, large conformational change causes head to be displaced along the filament
Force generating: new weak binding to actin filament, causes release of inorganic phosphate and tight binding to actin. Releases power stroke in which the head retains its original conformation and then releases the ADP

Question 3

How can organelles move through the cell?

Answer 3

movement of mesons attached to cellular organelles can move organelles along actin filaments

Question 4

How do muscle contracts?

Answer 4

The myosin header move towards the plus ends of the actin filaments pulling the z-discs together

Question 5

What are microtubules made up of?

Answer 5

long hollow cylinders made up of tubular monomers

Question 6

How big are microtubules?

Answer 6

25nm in diameter

Question 7

How are microtubules different from actin / intermediate filaments?

Answer 7

more rigid and straight

Question 8

Where do microtubules grow from?

Answer 8

Grow from a microtubule organising centre

Question 9

What are microtubules made up of?

Answer 9

Tubulin made up of a dimer of a and b tubulin

Subunits stack together to form a hollow cylindical microtubule

Question 10

How many subunits can be observed when looking down a microtubulin ?

Answer 10

13 protofilaments

Question 11

How are microtubules maintained?

Answer 11

balance between assembly and disassembly

A cell contains a mixture of microtubules and free tubulin
Microtubules are unstable allowing them to undergo rapid remodelling

Question 12

What is the centrosome?

Answer 12

Located in the cytoplasm just outside the nucleus

Microtubules grow out from the centrosome

Question 13

What are centrioles?

Answer 13

ylindrical organelle composed mainly of a protein called tubulin

Question 14

What controls the growth of microtubules?

Answer 14

GTP hydrolysis

Question 15

How is a GTP cap formed an what does it do?

Answer 15

If new subunits (which have GTP bound to beta tubulin) are added quicker than beta tubulins hydrolyses GTP, a GTP cap will form. When a GTP cap is present the microtubule end is stable and can continue to grow.

Question 16

How does a microtubule shrink?

Answer 16

If GTP is hydrolysed faster than new subunits are added the GTP cap is lost.

Question 17

How are microtubules stabilised?

Answer 17

Interacting proteins

Question 18

What is a summary of the overall function of microtubules?

Answer 18

Cellular organisation, movement of organelles, cell polarity
Cell division, mitosis, meiosis
Cilia and flagella

Question 19

What are two types of Motor proteins?

Answer 19

Kinesins and Dynesins

Question 20

What end of the microtubules do dyneins move?

Answer 20

Towards the minus end of the micrtubles

Question 21

What end of the microtubules do kinesins move?

Answer 21

Generally move towards the minus end of the microtubules

Question 22

What are two things that Kinesins and Dyneins have in common?

Answer 22

Both have two ATP binding heads and a tail

Both have ATPase activity

Question 23

What are Kinesins and Dyneins?

Answer 23

motor proteins

Question 24

What drives the movements of motor proteins along microtubules?

Answer 24

• ATP hydrolysis

provides conformation changes in the head that allows it to move along the microtubule

Question 25

Where is the Golgi situated in the cell and how does it get there?

Answer 25

It is situated on one side of the nucleus close to the centrosomes.
Dyneins pull it here

Question 26

Where is the ER directed to?

Answer 26

The opposite side of the cell to the Golgi

Question 27

What is the effect of Nocodazole?

Answer 27

Nocodazole is a drug that interferes with polymerisation of microtubules

• When cells are treated with nocodazole the microtubules disassemble, the Golgi fragments and is found more ‘spread out’ in cells.

Question 28

Where is the centrosome located?

Answer 28

just outside the nucleus

Question 29

what happens to the centrosome during mitosis?

Answer 29

Just before mitosis the centrosome duplicates

• The two centrosomes move apart
• microtubules grow out from each centrosome with their plus ends growing towards the equatorial plate forming spindle fibres

Question 30

what are the two drugs that interfere with microtubule assembly?

Answer 30

• Colchicine and taxol

Question 31

What is the mechanism of Colchicine?

Answer 31

Binds free tubular and prevents polymerisation into microtubules

Question 32

What is the mechanism of Taxol?

Answer 32

tightly binds microtubules and prevents them from losing subunits

Question 33

Where do cilia and flagella grow from?

Answer 33

Basal bodies

Question 34

How are cilia and flagella moved?

Answer 34

contain stable microtubules that are moved by dynein

Question 35

What is the primary function of cilia?

Answer 35

Cilia extend from the surface of many kinds of eukaryotic cell
Primary function of cilia is to move fluid over a cell or a cell through a fluid

Question 36

how are cilia and flagella microtubules arranged?

Answer 36

( 9 + 2)

Question 37

What is the function of the next links ins flagellum and cilia?

Answer 37

• stabilises the microtubules

- causes the structure to bend rather than slide