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Molecular Biology > Cytoskeleton exam 3 > Flashcards

Cytoskeleton exam 3 Flashcards

0
Q

This named structure provides support for the plasma membrane, provides mechanical strength and resistance to stress, changes shape of the cell, motility of the cell, and has a key role in cell division.

A

Cytoskeleton

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1
Q

What are the three families of Cytoskeletal proteins?

A

Actin filaments, microtubules, and intermediate filaments

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2
Q

This family of cytoskeletal proteins determines shape of the cells surface and are necessary for whole cell locomotion, secretion, and endocytosis

A

Actin filaments.

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3
Q

What is the function of Intermediate filaments?

A

provide mechanical strength and resist stress

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4
Q

cilia, flagella, centrioles, mitotic spindle, and the highways that direct intracellular transport are all examples of?

A

Microtubules.

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5
Q

Motor proteins are machines that convert energy of ATP hydrolysis into mechanical movement. They are called?

A

Accessory proteins

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6
Q

What are the two types of Actin?

A

G-actin (globular) and F-Actin (filamentous)

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7
Q

Microtubules are made up of?

A

Tubulin subunits

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8
Q

Keratin is a type of?

A

intermediate filament

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9
Q

during cell division, microtubules rearrange to form a?

A

bi-polar mitotic spindle

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10
Q

Actin filaments are replaced every?

A

48 hours

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11
Q

Polarity of the cytoskeleton infers there is a?

A

Apical surface and basolateral domain

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12
Q

Polarity of the cytoskeleton is maintained by?

A

the three families of cytoskeletal proteins (actin, microtubules,and intermediate filaments)

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13
Q

cytoskeletal filaments or polymers are held together by weak non covalent interactions, which allows for rapid?

A

assembly and disassembly

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14
Q

long linear strings of protein subunits joined end to end are called?

A

protofilaments

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15
Q

single protofilaments are thermally unstable and thus easier to?

A

break

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16
Q

multiple protofilaments are considered thermally stable therefore they can?

A

resist breakage by ambient thermal conditions. requires several bonds in the middle to be broken.

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17
Q

intermediate filaments are staggered side by side in order to tolerate?

A

bending and stretching. much like yarn

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18
Q

Nucleation refers to?

A

the assembly of small subunits into aggregation to form a larger filament. through the process of polymerization and depolymerization

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19
Q

whats the rate limiting step in filament nucleation?

A

the LAG phase- process of forming the initial aggregate

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20
Q

filament elongation or the growth phase are when?

A

subunits are quickly added onto the ends of nucleated filaments

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21
Q

the rate of addition of new subunits equal the rate of dissociation of subunits is defined in this stage?

A

Steady state of equilibrium

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22
Q

this heterodimer of the Alpha and Beta type form microtubules

A

Tubulin

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23
Q

Intermediate filaments are attached to which adhesive structures?

A

desmosomes (lateral-intercellular) and hemidesmosomes (basal lamina)

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24
Q

the critical concentration refers to?

A

the concentration of free subunits in the equilibrium phase

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25
Q

structural polarity of the microtubule is created in part by the?

A

arrangement of alpha and beta tubulins in a hollow, cylindrical structure consisting of 13 proto-filaments aligned in parallel.

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26
Q

Do microtubules have binding sites for ATP or GTP?

A

GTP

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27
Q

Actin monomers contain binding sites for this molecule

A

ATP

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28
Q

the “barbed end” has this type of tubulin and is also the fast growing end.

A

Beta tubulin- the Plus end

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29
Q

alpha tubulin associates with which end? also called the pointed end.

A

minus end

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30
Q

what proceeds spontaneously when delta G for addition of the monomer is less than zero, due to the monomer exceeding the critical concentration

A

Elongation

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31
Q

what are the two subunit types of Nucleotide hydrolysis?

A

T form- ATP/GTP bound

D form-ADP/GDP bound

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32
Q

if rate of polymerization is faster than the rate of hydrolysis of the bound nucleotide, the tip of the polymer remains in this form

A

T form. as an ATP or GTP cap.

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33
Q

hydrolysis lags behind on this side of the actin filament

A

plus end-fast addition

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34
Q

Treadmilling refers to this mechanism

A

the plus end growing while the minus end shrinks. this predominates Actin filaments!!! ** the plus end remains in the T form while the minus end adopts the D form.

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35
Q

if the nucleotide hydrolysis proceeds more rapidly than the subunit addition, the cap is lost and the microtubule will begin to shrink in which unstable state?

A

a catastrophic state

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36
Q

if GTP containing subunits are still adding to the shrinking end and there is enough to form a cap, then the microtubule growth can resume in this state?

A

the Rescue state!

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37
Q

hydrolysis of GTP after assembly changes confirmation of subunits making the protofilaments have weak bonds and they start to?

A

curve

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38
Q

Dynamic instability predominates in which cytoskeletal family of proteins?

A

microtubules

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39
Q

a staggered tetramer of two coiled-coil dimers is otherwise known as a ?

A

Proto-filament

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40
Q

eight parallel protofilaments pack together laterally to form this type of filament

A

an intermediate filament

41
Q

desmosomes and hemidesmosomes anchor which filaments?

A

intermediate filaments

42
Q

Listeria monocytogenes are pathogenic bacteria that invade enterocytes (intestinal) and affect which protein that shoots them around the cell like Comets?

A

Actin

43
Q

This actin subunit binds to actin and prevents assembly

A

Thymosin

44
Q

Profilin functions to?

A

speed up elongation

45
Q

this protein nucleates assembly to form a web and remains associated with the minus end

A

ARP 2/3 complex

46
Q

this protein nucleates assembly and remains associated with the growing plus end

A

Formin

47
Q

this actin protein binds ADP actin filaments to asscelerate disassembly in the minus end.

A

Cofilin

48
Q

Tropomyosin functions in?

A

stabilizing the actin filament

49
Q

which protein severs the actin filament and caps the plus end to prevent from growing?

A

Gelsolin

50
Q

this type of tubulin dimer nucleates assembly/growth and remains associated with the minus end.

A

y-TuRC (gamma tubulin ring complex)

51
Q

Kinesin 13 is a mictrotubule that enhances…

A

catastrophic disassembly at the PLUS end

52
Q

which proteins helps stabilize microtubules by binding along the sides?

A

MAPS

53
Q

microtubules are nucleated from a specific location, called?

A

MTOC-microtubule organizing center

54
Q

what is the major MTOC of animal cells called?

A

Centrosome

55
Q

this pair of cylindrical structures are embedded in the centrosome and arranged at right angles.

A

Centrioles

56
Q

microtubules are nucleated at the centrosome at which end?

A

minus end. with plus ends pointing outward that grow toward the periphery

57
Q

actin filaments in a cell cortex determine which two features of the cell surface?

A

shape and movement

58
Q

cell movements are catalyzed by these two factors…

A

ARP complex and formins

59
Q

what is the rate-limiting protein involved in filament nucleation that nucleates the actin filament growth from the minus end allowing elongation to occur at the plus end?

A

ARP 2/3

60
Q

Listeria m. has a surface protein called, ActA that activates this complex to cause local nucleation of cross linked actin filaments?

A

ARP2/3

61
Q

ARP complex works efficiently when the filaments are?

A

cross linked with a preexisting actin filament at a 70 degree angle

62
Q

How is there a large pool of actin polymers always kept available with all the nucleation of actin filaments occurring in the cell?

A

Thymosin- keeps actin monomers soluble so they are readily available for generating filaments

63
Q

this protein recruits actin monomers to the actin filament for polymerization

A

Profilin

64
Q

what is the difference between MAP2 and Tau?

A

MAP2-long, projecting linear domain with a second microtubule binding domain at the other end to form a stable bundle. widely spaced.

Tau-binds to N and C termini of microtubule. short projecting LOOP with closely packed bundles of microtubules.

65
Q

Cofilin prefers to bind to?

A

ADP containing actin filaments

66
Q

binding of Cofilin forces the filament to twist a little more tightly which weaken the bound actin subunits making it more easily severed. True or False?

A

true

67
Q

What are the two actin filament cross-linking proteins?

A
  1. Bundling proteins (parallel links-ex: alpha-actinin, fimbrin, and villin)
  2. Gel-forming proteins (angled actin filaments to create loose meshwork)
68
Q

Alpha actinin associates with ? to make actin filaments contract?

A

Myosin II

69
Q

the tight, parallel packing of actin filaments and Fimbrin prevent which protein from entering the bundle?

A

myosin II

70
Q

Villin can be found where in the body?

A

microvilli of intestinal tissue

71
Q

cells require the actin gel formed by? in order to extend membrane projections which help cells crawl across a solid surface

A

Filamin

72
Q

this family of proteins mediate the attachments between actin and the plasma membrane

A

ERM (ezrin, radixin, moesin)

73
Q

what activates ERM proteins?

A

phosphorylation

74
Q

of the cytoskeletal motor proteins, what determines the direction of movement?

A

the motor domain head

75
Q

what was the first motor protein identified in skeletal muscle?

A

myosin II

76
Q

the structure of Myosin II consist of?

A

two globular head heavy chains attached to coiled coil alpha helices, and four light chains at the N terminus that bind to ATP

77
Q

what results in skeletal muscle contraction?

A

ATP driven sliding of actin filaments towards the plus end

78
Q

this protein uses ATP to walk along a microtubule track, in the PLUS + direction, to move cargo vesicles and carry a binding site in the tail for a membrane-enclosed organelle

A

Kinesis

79
Q

Dynein is a microtubule motor protein that is directed toward the?

A

minus end

80
Q

binding of ATP on the back of the myosin head reduces the affinity for?

A

the head of actin and allows it to move along the filament

81
Q

skeletal movement works by?

A

coupling ATP hydrolysis to conformational change that propels the motor protein forward in a single direction

82
Q

the release of a phosphate group through ATP hydrolysis causes the movement of the actin filament, called the?

A

Power Stroke

83
Q

Cell migration is a cyclic process involving three activities?

A

Polarization and protrusion- actin polymerization at the plus end protrudes the lamellipodium

Adhesion and traction- involve Integrins

Re-traction- adhesions disassembled at the rear allowing the bulk of the trailing cytoplasm to be drawn forward.

84
Q

this plasma membrane protrusion if formed by migrating fibroblasts that are one dimensional and contain a core of long, bundled actin filaments.

A

Filopodia

85
Q

this protrusion is formed by epithelial cells, fibroblasts and neurons. they are two dimensional and sheet-like cross links with a mesh of actin filaments.

A

Lamellipodia

86
Q

formed by amoeba and neutrophils. these 3D projections are filled with an actin-filament gel.

A

Pseudopodia

87
Q

ARP complex nucleates actin filament growth from the MINUS end allowing elongation at the PLUS end. ARP is highly concentrated near the front of these projections where actin nucleation is most active.

A

Lamellipodia

88
Q

what is the role of Cofilin in lamellipodia?

A

Cofilin binds ADP-actin filaments that accelerate disassembly leading to Treadmilling. this polarity is the driving force for membrane protrusion.

89
Q

Rac acitivation promotes actin polymerization at the cell periphery leading to the formation of?

A

lamellipodia

90
Q

Cdc 42 activation triggers actin polymerization and bundling to form?

A

filopodia

91
Q

external signals (ex: antigenic peptides) trigger these GTPase monomer proteins to set up cell polarity by influencing the organization of the apparatus required for cell migration

A

Rho

92
Q

Rho activation promotes the bundling of actin filaments into?

A

stress fibers

93
Q

What are the major targets for Rac?

A

WASp (family of ARP nucleation activator proteins)

PAK (activates Filamin, inactivated Myosin light chain kinase-MLCK)
-decreased MLC phosphorylation leads to myosin II disassembly and decreased contractile activity

94
Q

activation of Rho leads to nucleation of actin filaments by ? and increases contraction by myosin II

A

formins

95
Q

where do Rac and Rho activation dominate?

A

Rac- is the front and Rho is in the back baby!!!

96
Q

microtubules are primarily nucleated at the centrosome which is mediated by?

A

y-tubulin

97
Q

actin filaments are nucleated near the plasma membrane and mediated by?

A

ARP complex and formin

98
Q

cell crawling, important in embryonic development and wound healing, requires the generation and maintenance of structure polarity influenced by?

A

external signals.

99
Q

during cell migration, protrusion is formed at the?

A

leading edge (assembly of new actin filaments)

100
Q

where does the newly protruded part adhere to?

A

substratum

Molecular Biology (3 decks)

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