Contractile Proteins

Question 1

which type of actin has polarity: globular or filamentous?

Answer 1

filamentous

Question 2

actin bundles

Answer 2

cross-linked actin into closely packed parallel arrays

Question 3

actin networks

Answer 3

loosely cross-linked actin into orthogonal arrays that form 3D meshworks with gel-like properties
- more flexible

Question 4

actin-bundling proteins

Answer 4

small, ridged proteins that force the filaments to align closely with each other

• cross-links actin
• determines the nature of association of filaments

Question 5

fimbrin

Answer 5

actin-bundling protein; binds to actin filaments as a monomer; holds two parallel filaments closely together
- ex: microvilli

Question 6

contractile bundles of actin

Answer 6

loosely bundled actin

- ex: contractile ring used in mitosis

Question 7

alpha-actinin

Answer 7

actin bundling protein; allows motor protein (myosin) to interact during contraction; binds as a dimer; filaments of actin are separated by a greater distance which allows myosin to interact during contraction

Question 8

filamin

Answer 8

actin bundling protein; binds actin as a dimer; can create 3D meshwork

Question 9

spectrin

Answer 9

actin binding protein in RBCs; forms actin network that forms a cortical cytoskeleton; this network interacts with membrane proteins via interactions with ankyrin, protein 4.1

Question 10

hereditary spherocytosis

Answer 10

decrease flexibility and stability of RBCs; caused by mutations in the cortical cytoskeleton proteins in RBCs (spectrin, ankyrin, 4.1)
- Sx: jaundice, anemia, splenomegaly

Question 11

pseudopodia

Answer 11

type of actin projection that is responsible for phagocytosis

Question 12

lamellipodia

Answer 12

broad, sheet like extensions of actin at the leading edge of a moving cell

Question 13

filopodia

Answer 13

thin projections of plasma membrane supported by actin bundles; formation and retraction of filopodia is based on regulated assembly and disassembly of actin filaments

Question 14

what driving force allows myosin to move along actin filaments

Answer 14

ATP hydrolysis

Question 15

head domain of myosin

- two parts

Answer 15

contains actin binding and ATP binding sites; ATPase activity

Question 16

neck domain of myosin

Answer 16

the flexible region; binds myosin light chain peptides

Question 17

tail domain of myosin

Answer 17

intertwines to bring myosin head regions in close proximity; binds membranes and organelles

Question 18

skeletal muscle myosin I

• neck size
• function

Answer 18

• 10-14 (small)

- interacting with membranes, endocytosis

Question 19

skeletal muscle myosin II

• neck size
• function

Answer 19

• 8 nm (v small)

- skeletal muscle contraction

Question 20

skeletal muscle myosin V

• neck size
• function

Answer 20

• 36 nm (v long)

- organelle transport

Question 21

how does rigor mortis occur

Answer 21

absence of ATP in the muscle –> myosin attaches to actin filaments and contracts and cannot relax

Question 22

what happens when ATP binds to myosin

Answer 22

a conformational change occurs causing release of actin; myosin then remains in “cocked state” –> binds to actin causing release of Pi (energy) –> “power stroke”

Question 23

“power stroke” of myosin bound to actin

Answer 23

release of P and i elastic energy which straightens myosin; moves actin filaments to the left

Question 24

as length of neck domain of myosin increases, ____

Answer 24

rate of movement increases

Question 25

what form is myosin in during low Ca2+ environements

Answer 25

folded

Question 26

what phosphorylates myosin

Answer 26

MLC (myosin light chain) kinase

Question 27

phosphorylation of myosin by MLC kinase causes ___

Answer 27

unfolding and activation of myosin

Question 28

what activates MLC kinase

Answer 28

calcium

Question 29

what dephosphorylates myosin

Answer 29

MLC (myosin light chain) phosphatase

Question 30

dephosphorylation of myosin causes

Answer 30

folding and relaxation of myosin (inactive)

Question 31

what causes the cleavage furrow in cytokinesis

Answer 31

myosin movement along actin filaments

Question 32

difference between myosin VI and myosin V in moving across filamentous actin

Answer 32

myosin VI moves towards the (-) end | myosin V moves towards the (+) end

Question 33

difference between dynein and kinesin in moving across filamentous actin

Answer 33

dynein moves toward (-) end | kinesin moves toward (+) end

Question 34

Duchenne Muscular Dystrophy - type of disorder - what is it

Answer 34

- X-linked recessive | - progressive muscle wasting due to mutations within dystrophin gene

Question 35

in-frame mutations in the dystrophin gene cause

Answer 35

becker muscular dystrophy

Question 36

out of frame mutations in the dystrophin gene cause

Answer 36

duchenne muscular dystrophy

Question 37

function of dystrophin

Answer 37

connects cytoskeleton to basal lamina; stabilizes the membrane of muscle cells