Cytoskeleton and Motor Proteins (Sayner)

Question 1

actin microfilaments

Answer 1

rigid, least deformable
can withstand some force then rupture

Question 2

actin functions

Answer 2

beneath plasma membrane: give shape to lipid bilayer
muscle contraction
cytokinetic ring
cell surface projections: motility

Question 3

actin monomers and polymers

Answer 3

G-actin monomers (globular) –> F-actin polymers (filamentous)

Question 4

Synthesis of actin

Answer 4

G-actin + ATP –> hydrolysis, binds F-actin –> F-actin + ADP

Question 5

F-actin is (polar/nonpolar)

Answer 5

Polar

Question 6

Treadmilling

Answer 6

F-actin
minus end: slow growing, subunit disassembly
plus end: fast growing, subunit addition

Question 7

actin inhibitors/toxins

Answer 7

cytochalasins
phalloidin
latrunculins

Question 8

cytochalasins

Answer 8

cause depolymerization of F-actin
bind plus end –> prevent addition

cy+ochalasin binds the plus end

Question 9

phalloidin

Answer 9

stabilize F-actin
bind to F-actin –> prevent depolymerization (impeding treadmilling)

Question 10

latrunculins

Answer 10

cause depolymerization of F-actin
bind G-actin –> prevent reincorporation (during treadmilling)

Question 11

Actin binding proteins (5)

Answer 11

profilin
thymosin
fimbrin
actin-related proteins (ARPs)
cofilin

Mnemonic: Proteins That Find Actin Cool

Question 12

profilin competes with…

Answer 12

thymosin

Question 13

profilin

Answer 13

binds G-actin at plus end –> allows minus end to polymerize
*promotes exchange of ADP for ATP –> accelerates assembly

ACIDIC membrane phospholipids promote

mnemonic: PROfilin PROmotes exchange

Question 14

thymosin

Answer 14

binds G-actin and prevents incorporation into filaments

mnemonic: reach between the THYs (thighs) to find the G (-actin)

Question 15

Fimbrin

Answer 15

cross links actin; forms tightly packed parallel bundles/arrays

Question 16

Actin-related proteins

Answer 16

ARP2 and ARP3

favor polymerization
activated by Rac

acts as seed/stabilizing platform for actin and minus end

builds a tree like web

Question 17

cofilin

Answer 17

mnemonic: coFilin binds F-actin

binds F-actin –> twists/applies mechanical stress –> breakage –> rapid disassembly

actin DEPOLYMERIZING factor

Question 18

cofilin is inactivated/phosphorylated by…

Answer 18

Rho A

Question 19

ARPs are activated by…

Answer 19

Rac

Question 20

protrusion

Answer 20

occurs at leading edge

chemokines –> Rac activation –> activates ARP 2/3 (polymerization) –> lamellipodia extension

cofilin –> disassembly behind leading edge

Question 21

attachment

Answer 21

integrins –> bind fibronectins –> link into actin cytoskeleton

Question 22

contraction

Answer 22

occurs at trailing edge

Rho –> activates myosine contractile machinery

Question 23

microtubules

Answer 23

train tracks
mitotic spindles

Question 24

microtubule synthesis

Answer 24

Question 25

polarity of microtubules

Answer 25

alpha: minus end beta: plus end (faster addition) mnemonic: be**t**a +

Question 26

T-form

Answer 26

microtubule stable form beta + G**T**P → **T**-form → strong, lateral contacts

Question 27

D-form

Answer 27

microtuble rapid depolymerization form hydrolysis → beta + G**D**P → **D**-form → curve/rapid depolymerization

Question 28

Microtubule orientation

Answer 28

**n**egative (minus end): toward **n**ucleus **p**ositive (plus end): toward **p**eriphery

Question 29

dynein

Answer 29

minus end directed toward nucleus

Question 30

kinesin

Answer 30

plus end directed toward periphery

Question 31

flagella arrangement

Answer 31

9 + 2 microtubule arrangement outer and inner dynein arms

Question 32

cilia are found:

Answer 32

in *sperm tails* and lining the: respiratory tract fallopian tubes urinary tract

Question 33

keratins

Answer 33

Types I and II intermediate filaments anchor into cell membrane

Question 34

Lamins

Answer 34

type v intermediate filament found in inner nuclear membrane function: nuceleoskeletal support/DNA protection