Lecture 18- Microtubules

Question 1

Microtubules are made of ____ _____ formed in protofilaments

Answer 1

tubulin heterodimers

Question 2

Where are Microtubules found in animal cells?

Answer 2

They are connected to centrosomes (MOSTLY) but they’re also found in RBC and neuron axon

Question 3

Why are most Microtubules dynamically unstable?
What are the functions of these microtubules?

Answer 3

It supports the cell- help resist compression and they’re good in early prophase (MTs extend and contract as they search for chromosomes)

Question 4

Why are Microtubules stable?
What are the functions of these Microtubules?

Answer 4

In prophase, once the MT has made successful contact with the chromosome, we want to stabilize that and that is stabilized by kinetochore proteins.

Ring of MTs inside the surface of RBC gives it its disc shape

There are MTs present in axons bc axons are too long to have their MTs connected to the centrosome (found in cell body).

Question 5

What is a cytoskeleton?

Answer 5

enormous protein filaments

protein filaments= made from many little proteins

Question 6

Proteins of cells are small but can make larger structures if we make chains of ___ proteins or bundles of ___ proteins

Answer 6

globular proteins and fibrous proteins

Question 7

What is the building block or protein subunit of Microtubule (protein filament)?

Answer 7

Tubulin

Question 8

Tubulin polypeptides are made by different genes on different chromosomes

True or False

Answer 8

True

Question 9

Can microtubules be organized into bundles?

Answer 9

Yes

Question 10

When we move tubulin heterodimer and add them, will it make microtubule longer or shorter?

Answer 10

it will make microtubule longer

Question 11

If we remove tubulin heterodimer from the (+) end, will it make microtubule longer or shorter?

Answer 11

Shorter

Question 12

Most MT are connected to ____ (which is located in the middle of the cell)

Answer 12

Centrosomes

Question 13

What happens if we take the centrosome and the MTs and remove them from the cell? Will they remain active?

Answer 13

They will remain active. The (+) end will grow or shrink and it will look like a spider stretching its legs from the body (which is the centrosome).

Question 14

Dynamic instability

Answer 14

When MT stop growing and shrink rapidly.

MT grow and shrink independently of their neighbors

Question 15

At what end are tubulins added and removed? (+) or (-)

Answer 15

Tubulins are added and removed from + (active) end

Question 16

Tubulin heterodimer (microtubule subunit) are made up of

Answer 16

Alpha-tubulin and Beta-tubulin

Question 17

Some microtubules could be growing and some could be shrinking at the same time

TRUE or FALSE

Answer 17

True

Question 18

What allows one MT to grow and one to shrink even if they’re side by side?
What regulates this?

Answer 18

Regulated by GTP

Question 19

Going from T Form (straight protofilament to T form which occurs?

A. Addition
B. Hydrolysis
C. Removal
D. Nucleotide replacement

Answer 19

Addition

Question 20

In going from T form (straight protofilament) to D form (curved protofilament) what happens?

A. addition
B. Hydrolysis
C. Removal
D. Nucleotide replacement

Answer 20

Hydrolysis

Question 21

In going from D form (curved protofilament) to D form what happens?

A. Addition
B. Hydrolysis
C. Removal
D. Nucleotide replacement

Answer 21

Removal

Question 22

In going from D form (curved protofilament) to T form (straight protofilament what happens?

A. Addition
B. Hydrolysis
C. Removal
D. Nucleotide replacement

Answer 22

Nucleotide replacement

Question 23

_____ ______ occurs when free in cytosol
(D -> T)

Answer 23

Nucleotide replacement

Question 24

____ occurs when part of a microtubule
(T -> D)

Answer 24

Hydrolysis

Question 25

As long as the MT keep growing, it will be on the ___ - form

Answer 25

T- form

Question 26

When tubulin heterodimers are in the __ form, they fall off and MT keep shrinking and shrinking

Answer 26

D form

Question 27

What is a catastrophe and how is it related to the growth of MT?

Answer 27

If MT grow into a region of the cell that doesn’t have any tubulin heterodimers available, it will catastrophe and then start shrinking.

Question 28

What is a rescue and how is it related to the growth of MT?

Answer 28

IF MT shrinks into a region where there’s a lot of tubulin heterodimers floating around, there will be rescue and then they will start growing again.

(Regain of GTP cap)

Question 29

Why is dynamic instability desirable?
WHy do want MTS growing and shrinking?

Answer 29

1. Cell support- it supports the cells by pushing outwards in all directions MTs help resist compression.
2. We want dynamic stability in early prophase- MTs extend and contract as they search for chromosomes.

Question 30

What are the two main forces acting on a cell?

Answer 30

Compression - trying to crush the cell
Tension- trying to rip the cell

Question 31

Why is dynamic stability desirable?
(When is it desirable)

Answer 31

1. Prophase- Successful MTs are stabilized when they contact chromosomes (once the MT has made successful contact with the chromosome, we want to stabilize that and that is stabilized by kinetochore proteins)
2. RBCs- ring of RBC that give its characteristic shape is due to a ring of MTs inside the surface
3. Neurons- axons have their own MTs since axons are too long to have their MTs connected to centrosome

Question 32

What proteins stabilize MTs in axons?

Answer 32

Tau proteins

Question 33

What are microtubules mad of?

Answer 33

Made of tubulin heterodimers formed in protofilaments

Question 34

Where are microtubules mostly found in animal cells?

Answer 34

Connected to centrosomes but they are also found in RBC and neuron axon