Actin Filaments (Microfilament) - Cytoskeleton

Question 1

What is the most important components of Action that make microfillaments unique in the cytoskeleton?

Answer 1

Actin makes microfillaments:
The smallest
The most flexible

Question 2

What are microfilaments made up of?

Answer 2

monomers (G-actin)

Question 3

What is microfilaments plymerized to?

Answer 3

polymer (F-actin)

Question 4

What is the monomers of microfilaments?

Answer 4

G-actin

Question 5

What is the polymer of microfilaments?

Answer 5

F-actin

Question 6

What do two polymers of F-actin form in a microfilament?

Answer 6

double-helix

Question 7

What makes up a double- helix in a microfilament?

Answer 7

two polymers of F-actin

Question 8

Explain the formation of a microfilament.

Answer 8

A microfilament is made up of monomer G-actin, that polymerize to an F-actin, creating a polymer. Two F-actin polymers twisted together create a double-helix, creating a microfilament.

Question 9

What are the 3 main key functions of the cytoskeleton?

Answer 9

1) maintain cell shape
2) allow key movements
3) adapt to compressive forces

Question 10

How are microfilaments involved in cell migration?

Answer 10

microfilaments can polymerize, squeeze in, and changes morphology to fit through tiny spaces

Question 11

What is Diapedesis and actins associates?

Answer 11

white blood cells change shape through actins to squeeze through the tiny intracapillary clefts

Question 12

Why would a white blood cell want to perform cell migration?

Answer 12

to move out of the blood stream and into interstial spaces to fight pathogens

Question 13

What is microfilaments role in cell division?

Answer 13

microfilaments seperate one cell by forming a constriction ring, allowing actin to pinch the cell in half producing two daughter cells.

Question 14

What stage of mitosis does actin form a constriction ring?

Answer 14

during cytokinesis

Question 15

How are microfillaments related to cell extension?

Answer 15

Actin are involved in the formation of Microvilli and Stereocilia.

Question 16

What are the two main parts of the cell membrane in microvilli and stereocilia?

Answer 16

Apical: top portion
Basal: bottom portion

Question 17

What occurs on the Apical surface of microvilli and stereocilia?

Answer 17

Actin forms a core of fingerlike projections or extensions, allowing movement

Question 18

Which cell has a a smaller extension on apical surface?

Microvilli
Stereocilia

Answer 18

Microvilli

Question 19

Which cell has a larger extension on apical surface?

Microvilli
Stereocilia

Answer 19

Stereocilia

Question 20

What is Microvilli’s role in the gastrointestinal tract?

Answer 20

food passing through GI tract come into contact with microvilli, increasing surface area for digestion

Question 21

What is Stereocilias role in the inner ear?

Answer 21

the stereocilia movement opens up channels in the inner ear for balance (vestibular) and hearing (cochlear)

Question 22

What is microfilaments role in muscle contraction?

Answer 22

microfilaments in muscles are know as Myofilaments (Actin + Myosin). The mysion clicks on with action, pulling the actin strans closer to other actin strands, causing shortening of myofilaments. = muscle contraction and relaxation.
(heavily involved in ATP production)

Question 23

What is a myofilament?

Answer 23

the microfilament of a muscle cell, made up of actin and myosin

Question 24

What does mysosin do in a muscle cell?

Answer 24

clickes on actin to pull actin strands closer together (shortening myofilaments) to cause muscle contraction/ reflaxation

Question 25

What role does microfilaments play in cell junctions?

Answer 25

prevents cell seperation through tight junctions and adheren junctions

Question 26

Whar are actin filaments key in the cell function formation?

Answer 26

actin strands help stick cells together and prevents seperation.

Question 27

What role does microfilamanets play in membrane transport?

Answer 27

actin responsible for invagination/ fuses on cell membrane allowing endosomes to perform endocytosis or extocytosis.

Question 28

What is actin assembled into filaments called?

Answer 28

F-actin

Question 29

Which has an ATP inding site? G-actin F-actin

Answer 29

G-actin

Question 30

Where is the ATP binding site located in a monomer G-protein?

Answer 30

between domains II and IV

Question 31

Actin filaments are: non-polar polar

Answer 31

polar (-) end: ATP binding cleft (gobular heads of myosin) (+) end: Barbed end (gobular heads of myosin)

Question 32

What end of actin filaments is pointed, where ATP binding cleft is located?

Answer 32

(-) end

Question 33

What end of actin filaments is the barbed end?

Answer 33

(+) end

Question 34

G-actin has intrinsic ATPase activty, thus is usually bound to: ATP ADP both

Answer 34

both ATP and ADP

Question 35

Where does polymerization and depolymerization occur in microfilaments?

Answer 35

at the ends of the filaments (not the middle)

Question 36

What are the three phases of polymerization?

Answer 36

1) nucleation 2) elongation 3) steady-state

Question 37

Which phase of polymerization occurs slowly?

Answer 37

nucleation

Question 38

Which phase of polymerization occurs relatively rapidly?

Answer 38

elongation

Question 39

When does elongation occur?

Answer 39

Only when g-protein concentration is above a critical concentration. (Cc)

Question 40

What phase of actin polymerization does elongation occur?

Answer 40

when G-actin concentration in above a Cc