Lecture 18- Microtubules Flashcards
Microtubules are made of ____ _____ formed in protofilaments
tubulin heterodimers
Where are Microtubules found in animal cells?
They are connected to centrosomes (MOSTLY) but they’re also found in RBC and neuron axon
Why are most Microtubules dynamically unstable?
What are the functions of these microtubules?
It supports the cell- help resist compression and they’re good in early prophase (MTs extend and contract as they search for chromosomes)
Why are Microtubules stable?
What are the functions of these Microtubules?
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).
What is a cytoskeleton?
enormous protein filaments
protein filaments= made from many little proteins
Proteins of cells are small but can make larger structures if we make chains of ___ proteins or bundles of ___ proteins
globular proteins and fibrous proteins
What is the building block or protein subunit of Microtubule (protein filament)?
Tubulin
Tubulin polypeptides are made by different genes on different chromosomes
True or False
True
Can microtubules be organized into bundles?
Yes
When we move tubulin heterodimer and add them, will it make microtubule longer or shorter?
it will make microtubule longer
If we remove tubulin heterodimer from the (+) end, will it make microtubule longer or shorter?
Shorter
Most MT are connected to ____ (which is located in the middle of the cell)
Centrosomes
What happens if we take the centrosome and the MTs and remove them from the cell? Will they remain active?
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).
Dynamic instability
When MT stop growing and shrink rapidly.
MT grow and shrink independently of their neighbors
At what end are tubulins added and removed? (+) or (-)
Tubulins are added and removed from + (active) end
Tubulin heterodimer (microtubule subunit) are made up of
Alpha-tubulin and Beta-tubulin
Some microtubules could be growing and some could be shrinking at the same time
TRUE or FALSE
True
What allows one MT to grow and one to shrink even if they’re side by side?
What regulates this?
Regulated by GTP
Going from T Form (straight protofilament to T form which occurs?
A. Addition
B. Hydrolysis
C. Removal
D. Nucleotide replacement
Addition
In going from T form (straight protofilament) to D form (curved protofilament) what happens?
A. addition
B. Hydrolysis
C. Removal
D. Nucleotide replacement
Hydrolysis
In going from D form (curved protofilament) to D form what happens?
A. Addition
B. Hydrolysis
C. Removal
D. Nucleotide replacement
Removal
In going from D form (curved protofilament) to T form (straight protofilament what happens?
A. Addition
B. Hydrolysis
C. Removal
D. Nucleotide replacement
Nucleotide replacement
_____ ______ occurs when free in cytosol
(D -> T)
Nucleotide replacement
____ occurs when part of a microtubule
(T -> D)
Hydrolysis
As long as the MT keep growing, it will be on the ___ - form
T- form
When tubulin heterodimers are in the __ form, they fall off and MT keep shrinking and shrinking
D form
What is a catastrophe and how is it related to the growth of MT?
If MT grow into a region of the cell that doesn’t have any tubulin heterodimers available, it will catastrophe and then start shrinking.
What is a rescue and how is it related to the growth of MT?
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)
Why is dynamic instability desirable?
WHy do want MTS growing and shrinking?
- Cell support- it supports the cells by pushing outwards in all directions MTs help resist compression.
- We want dynamic stability in early prophase- MTs extend and contract as they search for chromosomes.
What are the two main forces acting on a cell?
Compression - trying to crush the cell
Tension- trying to rip the cell
Why is dynamic stability desirable?
(When is it desirable)
- 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)
- RBCs- ring of RBC that give its characteristic shape is due to a ring of MTs inside the surface
- Neurons- axons have their own MTs since axons are too long to have their MTs connected to centrosome
What proteins stabilize MTs in axons?
Tau proteins
What are microtubules mad of?
Made of tubulin heterodimers formed in protofilaments
Where are microtubules mostly found in animal cells?
Connected to centrosomes but they are also found in RBC and neuron axon
