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MSK Final > Contractile Proteins > Flashcards

Contractile Proteins Flashcards

1
Q

What are the main cytoskeletal proteins?

A

Actin, actin binding proteins, and myosin

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2
Q

What determines the shape of the cell, its locomotion, and its ability to divide into two?

A

actin and actin binding proteins

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3
Q

What is the molecular machine that converts biochemical energy from ATP hydrolysis to mechanical energy that can move filaments on proteins or move organelles along filaments?

A

Myosin

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4
Q

What is each actin subunit referred to as?

A

g-actin

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5
Q

the polymerization of G actin forms what?

A

F actin

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6
Q

Why is the polarity of actin filaments important?

A

for their assembly and in establishing a unique direction of myosin movement relative to actin

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7
Q

the lag phase is also known as?

A

nucleation

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8
Q

the growth phase is also known as?

A

elongation

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9
Q

the equilibrium phase is also known as?

A

steady state

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10
Q

For a new actin filament to form, what is required?

A

subunits must assemble into an initial aggregate, where the nucleus is made up of 3 actin monomers

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11
Q

Process where subunits assemble into an initial aggregate, where the nucleus is made up of 3 actin monomers

A

nucleation

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12
Q

What do actin monomers have bound to them?

A

ATP

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13
Q

When actin filaments are assembled, what happens to the bound ATP?

A

it is hydrolyzed to ADP and Pi

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14
Q

Critical concentration

A

monomers and filaments of actin are in apparent equilibrium

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15
Q

Where are actin filaments particularly abundant?

A

beneath the plasma membrane

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16
Q

How is cross-linking of F-actin achieved?

A

accessory proteins

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17
Q

How is the nature of association of actin filaments determined?

A

by the size and shape of cross-linking proteins

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18
Q

What are the two general types of structures that actin filaments are assembled into?

A

Actin bundles and actin networks

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19
Q

cross-linked into closely packed parallel rays

A

actin bundles

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20
Q

loosely cross-linked in orthogonal arrays that form three-dimensional meshwork with more flexible gel-like properties

A

actin networks

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21
Q

Which general structure has the polarity of actin filaments different?

A

actin networks

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22
Q

what are parallel bundles made up of?

A

actin filaments and fimbrin monomer

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23
Q

what are contractile bundles made up of?

A

actin filaments and alpha-actin

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24
Q

Which actin bundle allows myosin II to enter the bundle?

A

contractile bundle

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25
Q

Which actin bundle supports projections of plasma membrane (e.g. microvilli)

A

parallel bundles

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26
Q

How many actin binding domains does fibrin have?

A

2

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27
Q

How does alpha-actinin bind?

A

as a dimer

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28
Q

What is an example of contractile bundles?

A

contractile ring used in mitosis

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29
Q

What is an example of parallel bundles?

A

microvilli.

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30
Q

What are two examples of actin bundles?

A

parallel bundles and contractile bundles

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31
Q

What is the large actin binding protein that holds actin filaments together in networks?

A

filamin

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32
Q

Which structure of actin filaments creates a #D meshwork?

A

actin-networks

33
Q

Erythrocytes contain what actin binding protein?

A

spectrin

34
Q

How does the spectrin-actin network interact with membrane proteins?

A

via interactions with ankyrin and protein 4.1

35
Q

How is hereditary spherocytosis caused?

A

caused by mutations in erythrocyte cortical cytoskeleton proteins (Spectrin, Ankyrin, and protein 4.1)

36
Q

How do myosin motor proteins move along actin filaments?

A

via ATP hydrolysis

37
Q

What part of the myosin contains the actin binding and ATP binding sites?

A

the head

38
Q

What part of the myosin is considered the flexible region and binds myosin light chain peptides?

A

the neck

39
Q

what part of the myosin binds membrane/organelles?

A

the tail

40
Q

Which myosin type has one heavy chain with a head domain and a neck domain?

A

Myosin I

41
Q

Which myosin head has two heavy chains-each with head and neck domain that binds two different light chains?

A

Myosin II

42
Q

Which myosin head has two heavy chains and six light chains per neck?

A

Myosin V

43
Q

Which myosin head is used in muscle contraction?

A

Myosin II

44
Q

Which Myosin head is used in transport?

A

Myosin V

45
Q

What causes the released myosin head to rotate into “cocked” state?

A

hydrolysis of ATP to ADP and Pi

46
Q

What causes the “powerstroke”

A

release of Pi and the elastic energy straightens myosin and moves the actin filament left

47
Q

Myosin will remain in the “cocked” state until when?

A

until it binds to actin filament

48
Q

What does the binding of actin cause the myosin to do?

A

release Pi, which will cause the power stroke

49
Q

The head remains tightly bound to the actin filament until when?

A

ADP is released, and fresh ATP is bound by the head

50
Q

What is the velocity of the powerstroke dependent on?

A

the length of the neck

51
Q

A longer myosin neck domain will cause?

A

An increase in the rate of movement

52
Q

What are thick filaments made up of?

A

6 myosin polypeptide chains

53
Q

When muscle fiber is at rest, what is the state of the myosin binding sites on actin?

A

they are covered by tropomyosin so that actin and myosin cannot interact

54
Q

How is the sarcomere structure stabilized?

A

by capping and scaffolding proteins

55
Q

How are actin filaments stabilized on their + ends?

A

by CapZ

56
Q

How are actin filaments stabilized on their - ends?

A

by tropmodulin

57
Q

a giant protein that extends along the actin filament all the way from the Z disk to tropomodulin

A

Nebulin

58
Q

Where does nebulin bind?

A

to tropomodulin

59
Q

What determines the length of the thin filaments?

A

the length of nebulin

60
Q

Has its head associated with the Z disk and extends to the middle of the thick filament

A

titin

61
Q

What is the purpose of titin?

A

its an elastic molecule that holds the thick filaments in the middle of the sarcomere and prevents overstretching

62
Q

What do titan mutations cause?

A

cardiomyopathies

63
Q

Under resting conditions, is the cytosolic calcium level high or low?

A

low

64
Q

What is the SERCA

A

Sarcoplasmic reticulum Ca2+ ATPase

65
Q

What does SERCA activity establish?

A

a reservoir of Ca2+ in the sarcoplasmic reticulum

66
Q

What is calcium induced calcium release?

A

depolarization stimulates the opening of voltage-gated Ca2+ channels in the sarcoplasmic reticulum. This brings in extracellular Ca2+, which then causes release of Ca2+ for the SR

67
Q

What happens after Ca2+ is released from the SR?

A

there is an elevation of cytosolic Ca2+ concentration in the myofibrils

68
Q

Elevated Ca2+ concentration in the myofibrils causes what?

A

conformation change in tropomyosin and troponin

69
Q

What activates contraction of smooth muscle?

A

phosphorylation of the myosin regulatory light chain

70
Q

A contractile ring is formed by what?

A

Bundles of F actin and Myosin II

71
Q

part of a protein complex that links the cytoskeleton of muscle fibers to the surrounding connective tissue (basal lamina)

A

dystrophin

72
Q

2 functions of dystrophin?

A

Shock absorber and stabilizes the sarcolemma

73
Q

Loss of dystrophin would lead to what?

A

duchenne’s muscular dystrophy

74
Q

What type of disorder is duchenne’s muscular dystrophy?

A

x-linked recessive

75
Q

who are DMD carriers?

A

females

76
Q

what is the milder form of DMD?

A

Becker muscular dystrophy

77
Q

2/3 of mutations in dystrophin result in what?

A

large internal deletions

78
Q

out-of-frame mutants?

A

DMD

79
Q

in frame mutants leads to what?

A

BMD

MSK Final (16 decks)

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