Actin And Cell Motility (Topic3)

Question 1

G actin

Answer 1

Monomer, can be added to polymer when bound to ATP

Question 2

F-actin

Answer 2

Polymer

-has polarity

Question 3

Formin

Answer 3

Assemble unbranded filaments

• Fh1 domain
• fh2 domain
• activated by Rho (binds RBD sequence)

Question 4

FH1 domain

Answer 4

Binds profilin and recruits g-actin ATP

Question 5

FH2 domain

Answer 5

2 of these domains associate into donut shape and bind 2 actin subunits

Question 6

Arp2/3

Answer 6

Nucleates branched filaments

-WCA protein WASp binds actin subunit

Question 7

Cdc42

Answer 7

Activates WASp

Also involved in formation of filopodia

Question 8

Thymosin

Answer 8

Decreases filament growth by binding g-actin ATP and preventing polymerization

Question 9

Profilin

Answer 9

Increases filament growth, binds g-actin ADP and enhances switch to ATP

• can bind (+) end of actin filament
• increased expression during cell growth

Question 10

Cofilin

Answer 10

Binds F-actin ADP bound subunits, causes filament to destabilize and break down
-causes tread milling in conjunction with profilin

Question 11

CapZ

Answer 11

Binds (+) end and inhibits addition or loss

Question 12

Tropomodulin

Answer 12

Bind (-) end and inhibits addition or loss

Question 13

Gelsolin

Answer 13

May bind (+) end
-with increased calcium, binds sides of actin filaments, inserts between subunits and creates shorter filaments

Question 14

Cytochalasin D

Answer 14

Toxin, binds (+) end and blocks addition

Question 15

Latrunculin

Answer 15

Toxin, binds and sequesters g-actin, inhibits addition to filament

Question 16

Jasplakinolide

Answer 16

Toxin, enhances nucleation, binds actin diners, lowers critical concentration

Question 17

Phalloidin

Answer 17

Toxin (angel of death mushroom)

Binds between subunits of f-actin and prevents depolymerization

Question 18

ActA protein

Answer 18

Expressed on surface of Listeria, activates Arp2/3, forms branching complex that forms “comet tail” which propels listeria around the cell

Question 19

alpha-actinin

Answer 19

Involved in formation of filopodia and stress fibres

• contractile bundles of muscle cells
• filaments arranges in opposite polarity

Question 20

Fibrin, villin

Answer 20

• parallel bundles in filopodia and villi

- actin filaments close together, same polarity

Question 21

Spectrin

Answer 21

Tetramer with 2 actin binding domains

Forms networks of filaments

Question 22

Filamin

Answer 22

Flexible region with actin binding domain, creates cross links between filaments

Question 23

Myosin

Answer 23

Motor protein, uses ATP to stimulate motion

Question 24

Sarcomere

Answer 24

Structure with repeating myosin and actin filaments, slide against each other during contraction, stabilized by Tropomodulin, CapZ and nebulous

Question 25

Nebulin

Answer 25

Extends along thin actin fibres in sarcomeres, determines length

Question 26

Titin

Answer 26

Attaches thick filaments in Sarcomere to z-disk

Question 27

Filopodia

Answer 27

Parallel bundles or actin in epithelial cells and fibroblasts

Question 28

Lamellopodia

Answer 28

Flat network of actin in neural growth cones

Question 29

Pseudopodia

Answer 29

3D network of actin in amoeba movement and phagocytosis

Question 30

Rho

Answer 30

Helps form stress fibres

Activated Formin

Question 31

Rac

Answer 31

Forms membrane Ruffles on leading edge, involved in formation of Lamellopodia through WAVp and arp2/3

Question 32

Classes of intermediate filaments

Answer 32

Keratins (epithelial cells)
Desmin, vimentin (muscle, glia)
Neurofilaments
Lamins (nucleus)