lecture 14 (cytoskeleton)

Question 1

What is the function of Actin filaments?

Answer 1

provides mechanical support, determines cell shape, and allows movement of the cell surface, thereby enabling cells to migrate, engulf particles, and divide.

Question 2

True or False: actin filaments are always stable

Answer 2

False, they are unstable but can be stable when associated with other proteins.

Question 3

What are actin binding proteins?

Answer 3

They are proteins that interacts with actin filaments to enable it to function

Question 4

What is the difference in length in microtubules and microfilaments?

Answer 4

Microfilaments is Shorter than microtubules but the total length of microfilaments is greater than microtubules

Question 5

what is polymerization of actin?

Answer 5

it is t a process, in which actin monomers both associate with and dissociate from the ends of actin filaments.

Question 6

the actin filaments grow by the addition of actin in both ends however the —– end will grow faster

Answer 6

plus end

Question 7

the rate of actin addition on both ends are proportional to:

Answer 7

the concentration of G-actin (unpolymerized actin)

Question 8

the rate of disassemble of actin is:

Answer 8

independent of G-actin (nearly constant)

Question 9

which type of nucleoside triphosphate does the actin monomers carry?

Answer 9

ATP

Question 10

what is the consequences of ATP hydrolysis in actin filament?

Answer 10

it reduces the strength of binding between the monomers and decreases the overall stability

Question 11

when the concentration of free actin is very high actin filament will —— at both ends.

Answer 11

will grow rapidly adding monomers at both ends

Question 12

what happens to the actin filments when the concentration of free actin is intermediate?

Answer 12

the filament will lose the subunit from the - end and at the same time adds them to the + end (treadmilling) a stable overall length

Question 13

what happens to the actin filments when the concentration of free actin is low?

Answer 13

lead to filament depolymerization.

Question 14

what happens to the actin filments when the concentration of free actin is high?

Answer 14

actin filaments will grow rapidly adding to both ends (polymerization)

Question 15

what are the three phases of G-actin polymerization?

Answer 15

1) nucleation
2) elongation
3) steady state

Question 16

nucleation:

Answer 16

when G-actin combine needs specifc concentration to start elongation

Question 17

elongation:

Answer 17

addition of actin to both ends and rate of loss is constant

Question 18

steady state:

Answer 18

the balance in addition and leaving rate (treadmilling)

Question 19

the rate of addition is —— greater than the negative end

Answer 19

12x

Question 20

if the concentration is less than —- it will shrink

Answer 20

0.12 micrometer

Question 21

if the concentration is more than —– it will grow

Answer 21

0.6 micrometer

Question 22

what is the name of the two protein that bind to actin monomers to prevent polymerization?

Answer 22

1) thymosin
2) profilin

Question 23

what is the name of the two protein that bind to actin monomers to promote polymerization?

Answer 23

1) formins
2) actin-related proteins (ARPs)

Question 24

types of actin-related proteins:

Answer 24

1) Actin-bundling proteins
2) cross linking protein
3) severing protein
4) capping protein (plus end blocking)

Question 25

when actin filaments associate with myosin motor protein it forms:

Answer 25

contractile bundles

Question 26

True or False: actin at cell cortex helps govern the shape of the plasma membrane

Answer 26

True

Question 27

how is the actin filaments linked in the plasma membrane?

Answer 27

by actin binding proteins

Question 28

cell crawling depends on

Answer 28

cortical actin

Question 29

how is lamellipodia and filopodia generated?

Answer 29

by actin polymerisation