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Cellular and Molecular Biology > Final: Ch 17 Myosin > Flashcards

Final: Ch 17 Myosin Flashcards

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1
Q

what are myosins

A

actin-based motor proteins that move along actin filaments

convert energy from ATP hydrolysis into movement along actin

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2
Q

myosin II

A

found in skeletal muscle

hundreds of molecules assemble into bundles

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3
Q

myosin V

A

binds vesicular cargo to transport it along actin filaments

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4
Q

domains of myosins

A

head

neck

tail

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5
Q

how to dissolve a myosin thick filament

A

solution of ATP and high salt

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6
Q

myosin II domains

A

2 heads and long tail connected by a flexible neck

tails intertwine and heads close together

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7
Q

myosin II has what type of activity

A

ATP hydrolysis (ATPase) in the S1 fragment

S1 also has F-actin binding site

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8
Q

all myosins have ___-_______ ATPase activity

A

actin-activated ATPase activity

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9
Q

sliding-filament assay

A

myosin attached to glass slide

actin filaments stained with phalloidin and ATP added

myosin heads walk toward + end, so looks like - end movement leads

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10
Q

tail domain

A

tailored to bind specific cargo

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11
Q

which domains of myosins are responsible for motor activity

A

head and neck (S1)

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12
Q

all myosin head domains convert what

A

ATP hydrolysis into mechanical work

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13
Q

myosin II assembles into _____ filaments

A

bipolar filaments

opposite orientations in each half so theres a cluster of head domains at each end

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14
Q

does myosin II have a short or long neck

A

short

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15
Q

myosin I

A

single headed

many functions

ex. connect actin filaments to membranes, endocytosis

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16
Q

myosin V domains

A

two heads and a long neck

tails dimerize

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17
Q

the length of the neck region affects the rate of myosin __________

A

movement

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18
Q

myosins move toward which end of the actin filament, except 1 myosin which moves toward the other end

A

+ end

myosin VI moves toward the - end

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19
Q

membrane-associated actin has their + end toward what?

A

the membrane

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20
Q

function of multinucleated skeletal muscle

A

produce gene products all along the cell

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21
Q

myosin heads do what along actin filaments

A

slide/”walk”

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22
Q

the hydrolysis of a single ATP molecule is coupled to each _____ taken by a myosin molecule along an actin filament

A

step

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23
Q

process of ATP-driven myosin movement along actin filaments

A

without ATP, the head is attached to F-actin

ATP binds the head, which releases the filament and hydrolyzes ATP –> ADP + Pi causing rocking

the myosin head binds actin

release of Pi is coupled to moving the actin filament forward (left) “power stroke”

ADP is released

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24
Q

the neck acts as a _____ point

A

pivot point

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25
the myosin step size is proportional to what
neck length tested by manipulating the genes for neck length (altered step size) and optical trap
26
step length of myosin II compared to myosin V
myosin V step length is 10x longer b/c of a very long neck (like a tether)
27
optical trap of myosin II
myosin on beads interacts with an actin filament held between 2 optical traps when ATP is added, the myosin pulls the actin and a computer records the distance
28
what did the optical trap of myosin II show
that myosin II binds, moves, and releases the actin it doesn't bind continuously
29
processive movement
myosin V takes sequential steps without releasing from actin one head is always in contact with the actin
30
does myosin V walk hand over hand on an actin filament?
yes
31
can myosin V transport organelles?
yes
32
do microtubules have classes that move in opposite directions?
yes
33
what do the tail regions of myosins determine
what kind of cargo it carries
34
myosin ____ filaments and actin _____ filaments in skeletal muscle slide past one another during _______
myosin thick, actin thin, contraction
35
skeletal muscle fiber properties
long and multinucleated striated sarcomeres
36
smooth muscle fiber properties
no sarcomeres mononucleate non-striated
37
sarcomere
arrangement of actin/myosin shortens by 70% during contraction
38
thick filaments are composed of what
myosin II bipolar filaments move toward Z disk where + ends are, causing contraction of the muscle
39
skeletal muscle is structured by ________ and ________ proteins
stabilizing, scaffolding actin capped by CapZ on the + end, and tropomodulin on the - end nebulin goes from Z disk to tropomodulin (where it binds) tintin is elastic and prevents overstretching
40
skeletal muscle contraction is initiated by an increase in cytosolic __
Ca2+
41
in skeletal muscle, a low cytosolic Ca2+ level is maintained by...
an ATPase that pumps Ca from the cytosol and into the sarcoplasmic reticulum
42
an action potential opens what in skeletal muscle
voltage-gated Ca channels in the SR membrane to raise cytosolic Ca concentration and induce muscle contraction
43
what effect does Ca have on skeletal muscle (thin-filament regulation)
changes tropomyosin and troponin which normally block myosin binding allows myosin-actin interactions and therefore contraction
44
contractile bundle
bundles composed of actin and myosin that are found in nonmuscle cells less organized than skeletal muscle fibers
45
in epithelial cells, contractile bundles are found as an ______ _____
adherens belt
46
3 types of contractile bundle
adherens belt - epithelium stress fibers -ECM contractile ring - cell division
47
skeletal muscle contraction is regulated by the ________-_______ complex bound to thin actin filaments
tropomyosin-troponin complex switches between contraction inducing state in the presence of Ca, and the relaxed state without Ca
48
how is smooth muscle contraction regulated
cycling of myosin II in response to extracellular signaling molecules phosphorylation/dephosphorylation of myosin regulatory light chain by myosin LC kinase (thick-filament regulation)
49
myosin V bound vesicles are carried along _____ filaments
actin
50
myosin V in budding yeast
carries secretory vesicles along actin filaments into the bud distributes organelles
51
myosin V in giant green algae
cytoplasmic streaming myosin V carries ER, which also moves cytoplasm
52
cell migration results from what
coordinated motions generated in different parts of the cell integrated with an endocytic cycle
53
how is cell migration initiated
formation of a large membrane protrustion at the leading edge of the cell - lamellipodium
54
cell migration of a fibroblast
membrane extension occurs at the leading edge where the network of actin filaments is nucleated by Arp2/3 (forms lamellipodium) some lamellipodia anchor to the substratum via focal adhesions the cell body is translocated forward by myosin II cortical contraction at rear of cell focal adhesions at the back of the cell are broken and integrins recycled by endocytosis freed tail snaps forward
55
the cell-adhesion molecules that mediate most cell-matrix interactions are membrane proteins called ______
integrins external domain binds ECM (fibronectin and collagen) cytosolic domain links them to the actin cytoskeleton
56
2 importances of focal adhesion attachment
prevents leading lamella from retracting attaches cell to the substratum, allowing for forward movement
57
what 3 small GTP-binding proteins control actin organization
Rho Rac Cdc42
58
what do growth factors like epidermal growth factor and platelet-derived growth factor do
bind cell surface receptors and stimulate cells to move and then divide ex. in a wound, platelets become active and secrete PDGF to attract fibroplasts and epithelial cells to the wound
59
what effect does dominant negative Rac have on wound healing
wound fails to close b/c Rac is needed to activate the Arp2/3 complex to form a lamellipodium
60
Cdc42 is critical for regulating ________ of cells
polarity dominant negative results in formation of leading edge, but movement in random directions
61
migrating cells are steered by _______ molecules
chemotactic ex. WBC are guided toward an infection by a tripeptide secreted by bacterial cells
62
common mechanism of chemotaxis
binding cell surface receptors activate intracellular signaling pathways remodel cytoskeleton through activation or inhibition of actin binding proteins
63
chemotaxis and amoebas
when stressed, these amoebas secrete cAMP which causes them to move toward each other they them form a slug and make starvation-resistant spores
64
membrane recycling in cell migration
membrane needed to form lamellipodia is provided from internalization of adhesion molecules (including integrins) from old focal attachments to front of cell
65
dominant active protein
mutant small GTPase locked in the active state
66
dominant active Cdc42
appearance of filopodia through Arp2/3 activation via the NPF WASp
67
dominant active Rac
membrane ruffles/lamellipodium
68
dominant-active Rho
stress fibers that contract
69
general model of how cell migration is controlled via Rac, Rho, Cdc42
Cdc42 orients cell oriented cell has high Rac activity in front to form lamellipodium Rho activity is high in the rear to assemble contractile structures and activate myosin II

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