Lecture 13

Question 1

Define Microfilaments

Answer 1

Smallest of the cytoskeletal filaments

Question 2

What are microfilaments involved in?

Answer 2

cell migration
amoeboid movement
cytoplasmic streaming

Question 3

Define actin

Answer 3

Very abundant protein in all eukaryotic cells

Question 4

Once synthesized actin

Answer 4

folds into globular shaped molecule that can bind atp or adp (G-actin)

Question 5

G actin molecules polymerize to form

Answer 5

microfilaments, f-actin

Question 6

Actins can be divided into

Answer 6

muscle-specific (alpha actins)

nonmuscle (beta actins)

Question 7

____ filaments are composed of two linear strands of polymerized G-actin wound into a helix

Answer 7

F-actin

Question 8

True or false: all actin monomers in a filament have the same orientation

Answer 8

true

Question 9

What type of monomers polymerize reversibly similar to tubulin assembly and how?

Answer 9

G-actin monomers

Lag phase and elongation phase

Question 10

Describe the plus end of a microfilament

Answer 10

barbed end

Question 11

Describe the minus end of a microfilament

Answer 11

Pointed end

Question 12

Polarity of microfilaments is reflected in more rapid addition or loss of

Answer 12

G-actin at the plus end than the minus end

Question 13

Growing microfilaments have ends that have

Answer 13

ATP actin

Question 14

Most of a microfilament is composed of

Answer 14

ADP actin

Question 15

After G-actin monomers assemble onto a microfilament

Answer 15

ATP bound to them is slowly hydrolyzed

Question 16

Define cytochalasins

Answer 16

Fungal metabolites that prevent the addition of new monomers to existing microfilaments

Question 17

Define Phalloidin

Answer 17

Stabilizes microfilaments and prevents their depolymerization

Question 18

What are stressed fibers?

Answer 18

Organized bundles in cells that adhere tightly to underlying substratum

Question 19

Describe the cell cortex

Answer 19

beneath plasma membrane, has actin cross-linked into a gel of microfilaments

Question 20

___ have a branched network of actin

Answer 20

Lamellipodia

Question 21

_____ microfilaments form highly oriented, polarized cables with plus ends toward tip of protrusion

Answer 21

Filopodia

Question 22

What do cells use actin-binding proteins for?

Answer 22

To precisely control where actin assembles and the structure of the resulting network

Question 23

If concentration of ATP-bound G-actin is high

Answer 23

Microfilaments will assemble until the G-actin is limiting

Question 24

Why is a large amount of free G-actin unavailable?

Answer 24

It is bound by thymosin Beta4

Question 25

When profilin concentration is high

Answer 25

polymerization is favored

Question 26

What competes with thymosin Beta 4 for G-actin binding?

Answer 26

Profilin

Question 27

What does ADF/ cofilin do?

Answer 27

Increase turnover of ADP actin at the minus end of microfilaments
Severs filaments and create new plus ends

Question 28

Whether microfilaments can grow depends on whether

Answer 28

their filament ends are capped

Question 29

___ binds to plus ends to prevent addition of subunits (via capping)

Answer 29

CapZ

Question 30

What is filamin’s function?

Answer 30

Filamin acts to “splice” joining two Microfilaments together where they intersect

Question 31

What is Gelsolin’s function?

Answer 31

Breaks actin microfilaments and caps the newly exposed plus ends, preventing further polymerization

Question 32

Define focal contacts/adhesions

Answer 32

Actin bundled into tightly organized arrays, needed for cells to make connections to ECM as they migrate

Question 33

What protein is prominent in focal adhesions?

Answer 33

alpha- actinin

Question 34

During cytokinesis

Answer 34

Microfilaments are connected to plasma membrane and exert force on it

Question 35

Actin forms a

Answer 35

treelike network