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Cell and Molecular Biology > Module 6: The Cytoskeleton (Myosin and Actin, Microtubules) > Flashcards

Module 6: The Cytoskeleton (Myosin and Actin, Microtubules) Flashcards

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1
Q

What enables the formation of contractile structures through the action of myosin motor proteins?

A

myosin and actin

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2
Q

What was the first motor protein identified? What does it generate?

A
  • Skeletal muscle myosin
  • Force for muscle contraction
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3
Q
  • A globular head domain containing the force-generating machine.
  • Composed of two heavy chains and two copies of each light chain.
A

Myosin II

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4
Q

This mediates an amino acid sequence forming an extended coiled-coil.

Myosin II; a process

A

heavy-chain dimerization

dimerization-joining two identical/similar molecular entities by bonds

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5
Q

Where do the light chains bind in myosin II?

A

Close to the N-terminal head

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6
Q

How are myosin heads oriented?

A

In opposite directions

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7
Q

Bind and hydrolyze ATP to walk toward the plus end of an actin filament.

A

myosin head

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8
Q

What makes the filament efficient at sliding?

A

opposing orientation of the myosin heads

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9
Q

What results from ATP-driven sliding of highly
organized arrays of actin filaments against arrays of myosin II?

A

muscle contraction

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10
Q

What uses structural changes in their ATP-binding sites to produce cyclic interactions with a cytoskeletal filament?

A

motor proteins

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11
Q

Propels motor proteins forward in a single direction to a new binding site along the filament (3)

processes

A

ATP binding, hydrolysis, and release

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12
Q

What generates each step of movement along actin which generated by swinging it?

it is 8.5 nm-long

A

lever arm

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13
Q

a piston-like helix which connects movements at the ATP-binding cleft in the head to small rotations

A

converter domain

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14
Q

Changes in the __ of the myosin are coupled to changes in its __ for actin. Allowing the __ to release its grip on the __ at one point and snatch hold of it again at another

A
  • conformation
  • binding affinity
  • myosin head
  • actin filament
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15
Q

What produces a single step of movement during the mechanochemical cycle? (3)

A
  1. Nucleotide binding
  2. nucleotide hydrolysis
  3. phosphate release
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16
Q
  1. ATTACHED: The __ is tightly locked onto an __ in a rigor configuration, which is short-lived in active muscles.
  2. RELEASED: ATP binds to the __, reducing its affinity for __ and causing it to detach.
  3. COCKED: ATP binding causes a conformational change, swinging the __ outward. ATP is hydrolyzed, but __ and __ remain bound.
  4. RE-BINDING AND POWER STROKE: The __ binds weakly to __, releases __, and undergoes a power stroke, losing its bound __.
  5. FORCE GENERATING: The cycle ends with the __ locked onto a new position in a __ configuration.

The cycle of structural changes used by myosin II to walk along an actin filament.

A
  1. myosin head; actin filament
  2. myosin head; actin
  3. lever arm; ADP; inorganic phosphate (Pi)
  4. myosin head; actin; inorganic phosphate (Pi); ADP
  5. myosin head; rigor

rigor means accurate

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17
Q

What are the steps in the cycle of structural changes used by myosin II to walk along an actin filament? (5)

A
  1. Attached
  2. Released
  3. Cocked
  4. Re-binding and Power Stroke
  5. Force Generating
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18
Q
  • are highly specialized for rapid and efficient contraction
  • form by the fusion of many separate cells into huge single cells

what type of cells?

A

muscle cells

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19
Q

What makes up the bulk of the cytoplasm inside muscle cells?
- It is a cylindrical structure 1–2 μm in diameter that is often as long as the muscle cell itself.

A

Myofibrils

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20
Q

What do myofibrils consist of?
- It is a long, repeated chain of tiny contractile units.
- About 2.2 μm long; gives the vertebrate myofibril its striated appearance

A

Sarcomeres

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21
Q

Consists of parallel and partly overlapping thin and thick filaments

A

Sarcomeres

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22
Q
  • actin and associated proteins
  • attached at their plus ends to a Z disc
  • minus ends overlapped with the thick filaments
A

thin filaments

composed of actin

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23
Q
  1. To what are the plus ends of thin filaments attached?
  2. Where do the minus ends of thin filaments overlap?
A
  1. Z-disc
  2. thick filaments

2) myosin

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24
Q

What are thick filaments composed of?

A

myosin

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25
Q

The arrangement of actin and myosin filaments within the sarcomere is __ with __ filaments evenly spaced between the __ filaments.

A
  • hexagonal lattice
  • actin
  • myosin
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26
Q

Myosin filaments sliding past the actin thin filaments causes…

A

sarcomere shortening

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27
Q

Does sarcomere shortening involve changes in the length of the filaments?

A

No, the length of the thin and thick filaments does not change.

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28
Q

Rise in cytosolic Ca²⁺ concentration initiates…

A

muscle contraction

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29
Q

What passes the signal to skeletal muscle?

muscle contraction and signaling

A

The nerve that stimulates it

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30
Q

What are the two features of muscle cells enabling rapid contraction? (2)

add short description

A
  1. Myosin motor heads coupled to ATP binding and hydrolysis
  2. Specialized membrane system for rapid signal relay
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31
Q

What specialized structures are involved in relaying the signal from the nerves to trigger an action potential in muscle cells? (2)

muscle contraction and signaling

A
  • T tubules (transverse tubules)
  • sarcoplasmic reticulum
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32
Q

What does the nerve signal trigger in the muscle cell?

muscle contraction

A

action potential

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33
Q

Where does the action potential travel in muscle cells?

muscle contraction

A

T (transverse) tubules

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34
Q
  • Ca2+ __ triggers the opening of __ in the __
  • Ca2+ flooding into the __ then initiates the contraction

muscle contraction and signaling

A
  • Ca2+ influx
  • Ca2+ release channels
  • sarcoplasmic reticulum
  • cytosol
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35
Q

Ca2+ dependence on muscle contraction is due entirely to a set of __.

A

specialized accessory proteins

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36
Q

An elongated protein that binds along the groove of the actin filament helix

muscle contraction

A

tropomyosin

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37
Q

A complex of three polypeptides: T, I, and C

muscle contraction

A

troponin

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38
Q

Pulls tropomyosin out of its normal binding groove, interfering with myosin head binding

muscle contraction

A

troponin I-T complex

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39
Q

When Ca²⁺ levels rise,
1. __ binds up to four molecules of Ca²⁺
2. __ releases its hold on actin

muscle contraction

A
  • Troponin C
  • Troponin I
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40
Q

What triggers contraction in smooth muscle cells?

A

Influx of calcium ions (Ca²⁺)

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41
Q

What kind of contractions do smooth muscle cells require? (2)

A

Slow and sustained contractions

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42
Q

Highly elongated spindle-shaped cells with a single nucleus

muscle contraction

A

smooth muscle cells

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43
Q

elevated intracellular Ca2+ levels regulate contraction by a mechanism that depends on…

A

calmodulin

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44
Q

What does Ca²⁺-bound calmodulin activate?

A

Myosin light-chain kinase (MLCK)

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45
Q

Induces phosphorylation of smooth muscle myosin on one of its two light chains

muscle contraction

A

Myosin light-chain kinase (MLCK)

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46
Q
  • What happens when light chains are phosphorylated?
  • What happens when light chains are dephosphorylated?

smooth muscle contraction

A
  • Smooth muscle contracts
  • Smooth muscle becomes inactive
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47
Q

Which muscle is the most heavily worked in the body?

A

heart

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48
Q

What specific isoforms do cardiac muscles express? (2)

A
  • cardiac muscle myosin
  • cardiac muscle actin
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49
Q

What condition is a common cause of sudden death in young athletes?
- genetically dominant inherited condition
- heart enlargement, abnormally small coronary vessels, disturbances in heart rhythm

A

Familial hypertrophic cardiomyopathy

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50
Q

At the molecular level, point mutations in the genes encoding __ or mutations in other genes encoding __

Familial hypertrophic cardiomyopathy

A
  • cardiac β myosin heavy chain
  • contractile proteins
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51
Q

Associated with minor missense mutations in the cardiac actin gene

A

dilated cardiomyopathy

myopathy-diseases affecting muscles that control voluntary movement.

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52
Q

contain small amounts of contractile actin-myosin II bundles

A

non-muscle cells

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53
Q

How are actin-myosin II bundles regulated?

A

myosin phosphorylation

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54
Q

What are the functions of actin-myosin II bundles in non-muscle cells? (4)

A
  • Mechanical support
  • cytokinesis
  • adhesion
  • forward motion of migrating cells
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55
Q

Where is myosin I found?

an organism

A

Acanthamoeba castellanii

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56
Q

What types of myosin are included in the myosin family? (2)

A
  • One-headed myosin
  • two-headed myosin
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57
Q

How many distinct myosin families are there?

A

37

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58
Q

How many myosin genes are included in the human genome?

A

40

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59
Q

How many myosin genes are expressed in the hair cells of the inner ear? How many mutations are known to cause hereditary deafness?

A
  • 9
  • 5
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60
Q

What structure in the inner ear is associated with myosins?

A

Stereocilia

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61
Q

Intracellular organization, including microvilli and endocytosis

A

myosin I

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62
Q
  • A two-headed myosin with a large step size; used for organelle transport along actin filaments.
  • It moves processively along actin filaments without letting go
A

myosin V

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63
Q
  • In this organism, actin cables in the mother cell point toward the bud, where actin is concentrated in patches at sites of cell wall growth
  • myosin carry wide range of cargoes
  • correct partitioning of organelles between mother and daughter cells
A

Saccharomyces cerevisiae

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64
Q
  • Highly dynamic and play diverse and important roles in the cell
  • Polymers of tubulin
  • Found in all eukaryotic cells
A

Microtubules

65
Q

a heterodimer composed of α-tubulin and β-tubulin

A

tubulin

66
Q

What is the binding site in tubulin for?

A

One molecule of GTP

67
Q

What condition can result from mutations in the human β-tubulin gene?

condition and what function is lost?

A

Paralytic eye-movement disorder due to loss of ocular nerve function

68
Q
  • A hollow cylindrical structure built from 13 parallel protofilaments
  • Composed of αβ-tubulin heterodimers stacked head to tail and then folded into a tube
A

Microtubule

69
Q

A microtubule is a hollow cylindrical structure built from 13 __. It is composed of __ stacked head to tail and then folded into a tube.

A
  • parallel protofilaments
  • αβ-tubulin heterodimers
70
Q

Protein-protein contacts in microtubules occur along the __; the “top” of the __ molecule forms an interface with the “bottom” of the __ molecule in the adjacent heterodimer; lateral contacts include α–α and β–β.

A
  • longitudinal axis
  • β-tubulin
  • α-tubulin
71
Q

Where does the addition and loss of subunits occur in microtubules?

A

Almost exclusively at the ends

72
Q

The subunits in each protofilament point in the __ direction; α-tubulins are exposed at the __ end and β-tubulins are exposed at the __ end.

microtubules

A
  • same
  • minus
  • plus
73
Q

What influences microtubule dynamics?

A

binding and hydrolysis of GTP

74
Q

Where does GTP hydrolysis occur in microtubules?

A

Only within β-tubulin

75
Q

What are the two forms of tubulin? (2)

A
  • “T form” (bound GTP)
  • “D form” (bound GDP)
76
Q

In microtubule dynamics, GTP tubulin tends to __, while GDP-tubulin tends to __.

A
  • polymerize
  • depolymerize

polymerize-molecules combine to form larger molecules

77
Q

What determines whether tubulin subunits at the end of a microtubule are in the T or D form? (2)

A
  • relative rates of GTP hydrolysis
  • tubulin addition
78
Q

During a high rate of tubulin addition, the tip of the polymer remains in the __ form, creating a __.

microtubule dynamics

A
  • T
  • GTP cap
79
Q

A high rate of __ or a decrease in __ cause a sudden change from T form to D form in microtubules.

A
  • GTP hydrolysis
  • tubulin addition
80
Q

The rapid interconversion between a growing and shrinking state

microtubule dynamics

A

dynamic instability

81
Q

A transition from growth to shrinkage

microtubule dynamics

A

catastrophe

82
Q

A transition from shrinkage to growth

microtubule dynamic

A

rescue

83
Q

Tubulin subunits with __ bound to the __ produces straight protofilaments that make strong and regular lateral contacts

A
  • GTP
  • β-monomer
84
Q

The hydrolysis of __ to __ in tubulin causes a subtle conformational change in the protein, resulting in __

A
  • GTP to GDP
  • curvature/curve
85
Q

In the microtubule structure, it constrains the curvature of the protofilaments, making the ends appear straight

A

GTP cap

86
Q

When the terminal subunits of tubulin have hydrolyzed GTP, the __ is removed, causing the protofilaments to __.

A
  • constraint (GTP cap)
  • spring apart
87
Q

What type of drugs inhibit microtubule functions? (2)

A
  • polymer-stabilizing drugs
  • polymer-destabilizing drugs
88
Q

They cause microtubule depolymerization (2)

Drugs

A
  • colchicine
  • nocodazole
89
Q
  • binds to and stabilizes microtubules, increasing tubulin polymerization
  • Used to treat cancers of the breast and lung

Drug

A

taxol

aka paclitaxel

90
Q

What is a common effect of microtubule-depolymerizing and polymerizing drugs?

A

kill dividing cells

91
Q

What is the concentration of tubulin subunits required for spontaneous nucleation of microtubules?

level

A

very high

92
Q

Involved in the nucleation of microtubule growth at smaller amounts

A

γ-tubulin

93
Q

A specific intracellular location where microtubule nucleation occurs

A

microtubule-organizing center (MTOC)

94
Q
  • What is the complex where γ-tubulin and two accessory proteins bind to create a spiral ring template for microtubule formation?
  • How many protofilaments does a microtubule have, as created by this template?
A
  • γ-tubulin ring complex (γ-TuRC)
  • 13
95
Q

A well-defined microtubule-organizing center (MTOC) located near the nucleus

A

centrioles

96
Q

Microtubules are nucleated at their __ ends; __ ends point outward and continuously grow and shrink

centrosomes

A
  • minus
  • plus
97
Q

A pair of cylindrical structures embedded in the centrosome, arranged at right angles in an L-shaped configuration; barrel shape with striking ninefold symmetry

A

Centrioles

98
Q

Where does microtubule nucleation take place in the centrosome?

A

pericentriolar material

99
Q

A microtubule-organizing center (MTOC) embedded in the nuclear envelope, found in budding yeast, fungi, and diatoms.

A

spindle pole body

100
Q

Do fungi or plants have centrioles?

A

No

101
Q

What do fungi and plants use to nucleate their microtubules?

A

γ-tubulin

102
Q

Dynamic plus ends point outward toward the cell periphery, and stable minus ends are collected near the nucleus.

what configuration is this?

A

aster-like configuration

103
Q

It has the ability to find the center of the cell, establishing a general coordinate system used to position many organelles within the cell.

A

microtubule cytoskeleton

104
Q

Microtubules in cells exhibit a much higher __ rate, a greater __ frequency, and extended pauses in microtubule growth.

A
  • polymerization
  • catastrophe
105
Q

modulate filament dynamics and organization.

microtubule

A

Microtubule-binding proteins

106
Q
  • proteins that bind to microtubules, stabilizing them against disassembly and mediating interactions with other cell components.
  • prominent in neurons, specifically in axons and dendrites extending from the cell body.
  • have at least one domain that binds to the microtubule surface and another that projects outward.
  • targets of several protein kinases
A

microtubule-associated proteins (MAPs)

107
Q

__ has a long projecting domain that forms bundles of stable microtubules that are widely spaced, while __ has a shorter projecting domain that forms bundles of more closely packed microtubules.

A
  • MAP2
  • tau
108
Q

Proteins that bind the __ of microtubules influence the stability and dynamics of microtubules.

A

ends

109
Q
  • The frequency of __ refers to the transition from a growing to a shrinking state.
  • The frequency of __ refers to the transition from a shrinking to a growing state.
A
  • catastrophe
  • rescues
110
Q

bind to microtubule ends and prying protofilaments apart, promoting disassembly.

A

Catastrophe factors (kinesin-13)

111
Q

protects microtubule minus ends from the effects of catastrophe factors.

A

Nezha/Patronin

112
Q

enriched at microtubule plus ends, binds free tubulin subunits, and delivers them to the plus end, promoting polymerization and counteracting catastrophe factor activity.

A

XMAP215

113
Q

stabilized by association with a capping protein or the centrosome and serve as depolymerization sites.

microtubules

A

minus ends

114
Q

explore and probe the entire cell space.

microtubules

A

plus ends

115
Q

Accumulate at the active plus (+) ends of microtubules and appear to move around the cell as passengers on rapidly growing microtubules, dissociating when microtubules shrink.

A

plus-end tracking proteins (+TIPs)

116
Q

They modulate the growth and shrinkage of microtubules and control their positioning. (2)

A
  • kinesin-related catastrophe factors
  • XMAP215
117
Q

a small dimeric protein that attaches to the plus end of microtubules, allowing the cell to harness the energy of polymerization for positioning spindles, chromosomes, or organelles.

A

EB1

118
Q

Cells __ unpolymerized tubulin subunits to maintain a pool of active subunits.

A

sequester

isolate or hide away

119
Q
  • binds to two tubulin heterodimers and prevents their addition to the ends of microtubules, decreasing the effective concentration of tubulin subunits.
  • Phosphorylation of this inhibits its binding to tubulin.
  • expressed in the neurons of the amygdala.

microtubule dynamics

A

stathmin (Op18)

120
Q

For a microtubule to be severed, __ longitudinal bonds must be broken, __ for each protofilament.

how many

A
  • thirteen
  • one
121
Q

meaning “sword,” is made up of two subunits where the smaller one hydrolyzes ATP to perform the actual severing, while the larger subunit directs this to the centrosome.

microtubule dynamics

A

katanin

122
Q

transport cargo and perform various functions along microtubules.

A

Motor proteins

123
Q

What are the two main types of motor proteins associated with microtubules? (2)

A
  • Kinesins
  • Dyneins
124
Q
  • carries membrane-enclosed organelles away from the cell body toward the axon terminal by walking toward the plus end of the microtubule.
  • Similar to myosin II; both have two heavy chains per active motor, and the motor domain is the common element.
  • have 14 distinct families
  • uses ATP hydrolysis
  • have a binding site in the tail for another microtubule.
A

kinesin-1 (conventional kinesin)

125
Q

How many distinct families are there in the kinesin superfamily?

A

14

126
Q

Where is the motor domain located in kinesins, and what direction do they move? (2)

microtubule dynamics

A
  • motor domain - N-terminus of the heavy chain
  • kinesins move toward the plus end
127
Q

In kinesin-1 function, __ is used to facilitate the movement and depolymerization of microtubule ends.

a reaction

A

ATP hydrolysis

128
Q
  • In kinesin-1 function, small movements at the nucleotide-binding site regulate the (1)__ and (2)__ of the motor head domain to a long linker region.
  • Kinesins move 8 nm toward the (3)__ end, with cycles of linker (1)__ and (2)__ allowing for hand-over-hand stepwise movement.
A
  • docking
  • undocking
  • plus
129
Q

In kinesins, these cycles are closely coordinated to ensure efficient movement along the microtubule.

A

nucleotide-hydrolysis cycles

130
Q
  • minus-end directed motors
  • consists of one, two, or three heavy chains and a large variable number of associated intermediate, light-intermediate, and light chains.
  • the largest of known molecular motors and the fastest.

microtubule dynamics

A

Dyneins

131
Q

homodimers made up of two heavy chains.

microtubule dynamics

A

cytoplasmic dynein

132
Q

involved in organelle and mRNA trafficking, positioning the centrosome and nucleus during cell migration, and constructing the microtubule spindle.

microtubule dynamics

A

cytoplasmic dynein I

133
Q

transports material from the tip to the base of cilia.

microtubule dynamics

A

Cytoplasmic dynein II

134
Q

Specialized for rapid and efficient sliding movements of microtubules that drive the beating of cilia and flagella.

microtubule dynamics

A

Axonemal dyneins (ciliary dyneins)

135
Q

The general rule regarding nucleotide hydrolysis in __, there is a coupling of nucleotide hydrolysis to microtubule binding and unbinding, as well as to a force-generating conformational change.

microtubule dynamics

A

dyneins

136
Q

In the interphase of cells, they are responsible for the transport and positioning of membrane-enclosed organelles.

microtubule dynamics

A

cytoskeletal motors

137
Q
  • Kinesins are responsible for fast __, moving materials toward the cell’s periphery.
  • Cytoplasmic dyneins are responsible for __, moving materials toward the cell center.

microtubule dynamics

A
  • antegrade axonal transport
  • retrograde axonal transport

antegrade - forward; retrograde - backward

138
Q

What type of movements require the action of minus-end directed cytoplasmic dynein?

microtubule dynamics

A

Centripetal movements

139
Q

What type of movements require kinesin motors? (toward the periphery require plus-end directed kinesin motors)

microtubule dynamics

A

Centrifugal movements

centrifugal - moving away from the center

140
Q
  • The endoplasmic reticulum (ER) is located at the __ of the cell.
  • The Golgi apparatus is located near the __.
A
  • edge
  • cell center
141
Q
  • a large protein complex associated with cytoplasmic dynein that helps translocate organelles effectively.
  • a short, actin-like filament that forms the actin-related protein Arp1.

microtubule

A

Dynactin

142
Q

Defects in microtubule-based transport have been linked to neurological diseases such as __, where cells fail to migrate to the cerebral cortex.

A
  • smooth brain (lissencephaly)
143
Q

a dynein-binding protein required for nuclear migration in several species; its absence leads to nuclear-migration defects as migrating neurons fail to attach to dynein.

microtubule

A

Lis1

144
Q

regulate their activity, resulting in changes in the position of organelles or whole cell movements.

microtubule

A

motor proteins

145
Q

contain large pigment granules that can alter their location in response to neuronal or hormonal stimulation.

microtubule; a cell

A

Fish melanocytes

146
Q

a structure that forms during cell division, allowing the segregation of chromosomes; its assembly depends on the reorganization of the interphase array of microtubules to form a bipolar array.

A

mitotic spindle

147
Q

In __, microtubules have mixed polarities, while in __, the minus end points back toward the cell body, and the plus end points toward the axon terminals.

A
  • dendrites
  • axons
148
Q

What structures are filled with bundles of microtubules in neurons? (2)

A
  • Axons
  • dendrites
149
Q

specialized motility structures made from microtubules and dynein, with a bundle of microtubules at their core. (2)

A
  • Cilia
  • Flagella
150
Q

__ enable cells to swim through liquid media with an undulating motion, while __ beat with a whiplike motion resembling the breaststroke.

A
  • Flagella
  • Cilia

undulating-resembling the motion of waves

151
Q
  • the core structure of cilia and flagella, composed of microtubules and their associated proteins, arranged in a distinctive pattern.
  • consists of nine doublet microtubules arranged in a ring around a pair of single microtubules in the center.
A

axoneme

152
Q

forms bridges between neighboring doublet microtubules around the circumference of the axoneme, facilitating the bending motion necessary for ciliary and flagellar movement.

A

Axonemal dynein

153
Q

What condition is caused by hereditary defects in axonemal dynein?
- Symptoms include sinus inversus due to disrupted fluid flow in the embryo, male sterility due to immotile sperm, and a high susceptibility to lung infections due to paralyzed cilia.

sinus inversus-organs in chest & abdomen positioned in a mirror image

A

Kartagener’s syndrome (a type of primary ciliary dyskinesia (PCD))

154
Q

What protein is found in bacterial flagella?

A

flagellin

155
Q
  • nonmotile counterpart of cilia and flagella
  • specialized cellular compartments or organelles
  • shares structural features with motile cilia
A

primary cilium

155
Q

consists of nine groups of fused triplet microtubules arranged in a cartwheel structure.

A

centriole

156
Q

In the nasal epithelium, primary cilia are involved in __ and __.

A
  • odorant reception
  • signal amplification
157
Q

In rod and cone cells, primary cilia are responsible for converting __ signals into __ signals.

A
  • light
  • neural

Cell and Molecular Biology (20 decks)

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