Cytoskeleton

Question 1

main function of the cytoskeleton

Answer 1

cell shape, cell wall formation, intracellular movement, cell metabolism

Question 2

cytoskeleton is composes of what 2 parts mainly

Answer 2

microtubules and actin filaments

Question 3

Microtubules

structure of MTs (3 main pieces)

Answer 3

tubulin dimers, 13 protofilaments, polarity

Question 4

MTs are composed of 2 types tubulin dimers:

Answer 4

alpha-tubulin and beta-tubulin

Question 5

Microtubules are formed by 13 protofilaments that form [blank]

Answer 5

a hollow tube

Question 6

MTs exhibit polarity, at what end does growth occur

Answer 6

growth at the (+) end, it also has a (-) end

Question 7

Are MTs dynamic?

Answer 7

Yes, constantly growing and shrinking, which makes them a bit unstable

Question 8

How is the instability of MTs regulated

Answer 8

regulated by the GTP/GDP state of the tubulin dimers

Question 9

MTs are approx how long

Answer 9

25nm tubes

Question 10

actin filaments are approx how long

Answer 10

7nm, aka microfilaments

Question 11

GTP bound beta tubulin’s form? straight or bent? assembly or dissasembly?

Answer 11

GTP bound beta tubulin is straight, assembly

Question 12

GDP bound beta tubulin is straight or bent? assembly or dissasembly?

Answer 12

GDP beta tubulin is bent, dissasembly

Question 13

MT Polymerization and Catastrophe

how does a MT grow

Answer 13

add GTP dimers at the (+) end

Question 14

how does MT catastrohpe happen

Answer 14

loss of GTP cap due to hydrolysis leads to rapid breakdown

Question 15

how does EBI (End Binding Protein) influence MT dynamics

Answer 15

• binds to (+) end to GTP cap
• stablize elongation, prevent catastrophe
• guides growth and speed

Question 16

where does MT nucleation happen

Answer 16

nuclear envelope and pre-existing MTs

Question 17

what does γ-Tubulin Ring Complex (γ-TuRC) do

Answer 17

acts as a template for forming new MTs, providin starting point and polarity for GTP cap to attach and begin elongation and polymerization

Question 18

cell wall structure and formation

[blank] MTs guide the movement of [blank], which lays cellulose fibers in the cell wall.

Answer 18

cortical, cellulose synthase

Question 19

MTs are crucial for organizing cellulose production, impacting cell wall [blank]

Answer 19

rigidity

Question 20

Actin filaments are composed of [blank] monomers, which polymerize into [blank]

Answer 20

G-actin (globular), F-actin (filamentous)

Question 21

Actin filaments are flexible and they can be strenghtened by [blank]. They do not form [blank] bonds

Answer 21

bundling, covalent

Question 22

how does actin filament polymerization happen

Answer 22

ATP binds to G actin monomers, profilin plays a key role

Question 23

how does profilin regulate polymerization in actin filaments

Answer 23

makes sure atp binds to g-actin at (+ end)

Question 24

apart from prolifin, what else regulates polymerization

Answer 24

actin binding proteins regulate by promoting or repressing polymerization

Question 25

two types of nucleation (formation) for actin filaments

Answer 25

formin-mediated, ARP 2-3 complex- mediated

Question 26

formin mediated nucleation involves

Answer 26

unbranched, linear actin filaments, which recruits G-actin at the (+) end.

Question 27

ARP 2-3 complex mediated nucleation involves

Answer 27

nucleation of branched AFs by growing (nucleating) off existing filaments, aiding in cell shape and motility.

Question 28

function of AFs in plant cells

Answer 28

-vesicle delivery -growth in pollen tubes -found in cortical and transvacuolar strands of cytoplasm

Question 29

what is treadmilling

Answer 29

MTs glide through the addition and loss of dimers at opposite ends, maintaining their structure while changing

Question 30

Real-time observations reveal that MTs add or lose up to 20 dimers per second at the (+) end. What does this tell us?

Answer 30

allows for flexibility in cell structure

Question 31

Actin filaments can form branches via the ARP 2/3 complex. Why is this important?

Answer 31

helps cells adapt shape to environment, especially in epidermal cells

Question 32

Phalloidin, a toxin that binds to [blank]? What does it do?

Answer 32

F-actin, used to stain and visualize actin filaments

Question 33

α-tubulin always binds [blank], while β-tubulin cycles between [blank]

Answer 33

GTP, GTP and GDP states