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Block 4 Week 1 Meg > Baker: Muscle Contraction and Regulation > Flashcards

Baker: Muscle Contraction and Regulation Flashcards

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1
Q

Levels of organization within a skeletal muscle

A 
myofilaments
myosin thick filaments and actin thin filaments
myofibril
muscle fiber
muscle fibers
muscle
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2
Q

There are many myosin (blank) and all have similar (blank) domains. They have differences in the (blank) that correspond to differences in cargo and regulation.

A

types; motor; tail

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3
Q

Which type of myosin is involved in cell division?

A

Myosin IIa

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4
Q

Which type of myosin is involved in melanosome transport and certain neurological functions?

A

Myosin V

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5
Q

What is the disease caused by a point mutation in myosin Va which leads to hypopigmentations and neurological defects?

A

Griscelli’s Syndrome

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6
Q

Which type of myosin is involved in maintaining organization of actin-filled stereocilia?

A

Myosin VI and Myosin VII

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7
Q

What are mutations in myosin VI and VII associated with? What are certain myosin VII mutations associated with?

A

hearing loss; Usher syndrome

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8
Q

Muscle myosin II is a (blank). Each heavy chain has what two components?

A

dimer; motor domain and a tail

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9
Q

All myosins are (blank)-based motors, and all but myosin VI are (blank)-end directed.

A

actin; plus

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10
Q

Sources for ATP in the muscle?

A
  1. ATP
  2. creatine phosphate
  3. anaerobic glycolysis
  4. aerobic glycolysis
  5. lipolysis
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11
Q

Under anaerobic conditions, what builds up from pyruvic acid? Does the Krebs cycle and ox phos occur?

A

lactic acid; no

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12
Q

When oxygen is present, the (blank) pathway will proceed. What are the end products?

A

aerobic; CO2, water, 36 ATP

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13
Q

At the start of muscle contraction, a myosin head lacking a bound nucleotide is locked tightly onto an actin filament in a (blank) confirmation. In an actively contracting muscle, this state is short-lived, because it is terminated when ATP binds. This is the (blank) state.

A

rigor; attached

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14
Q

In the (blank) state, a molecule of ATP binds to the back of the myosin head, this causes a change in conformation of the domains that make up the actin binding site. This reduces the affinity of the head for (blank) and allows it to move along the filament.

A

released; actin

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15
Q

In the (blank) state, the cleft closes like a clam shell around the ATP and causes the head to be displaced from the actin filament. ATP is hydrolyzed, but ADP and Pi remain tightly bound to the protein.

A

cocked

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16
Q

In the (blank) state, a weak binding of the myosin head to a new site on the actin filament causes release of Pi. This occurs with a tight binding of the head to actin.

A

force-generating

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17
Q

What is this: the force-generating change in shape during which the head regains its original confirmation. During this time, the head loses its bound ADP, and returns to the start of a new cycle.

A

power-stroke

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18
Q

At the end of a cycle of muscle contraction, the myosin head is again locked tightly to (blank) in a rigor configuration. *Note that the head has moved to a new position on the actin filament.

A

the actin filament

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19
Q

Myosin V has a much (blank) lever arm than Myosin II, so it can move across the actin filament in less cycles.

A

larger

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20
Q

Myosin V is a (blank) dute ratio motor. What is Myosin V’s duty ratio? What does Myosin V do?

A

high; >50% (one head of the myosin molecule must be bound to the actin filament for about 50% of the ATPase cycle); myosin V transports vesicles in cells

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21
Q

Myosin II is a (blank) duty ratio motor. What is Myosin II’s duty ratio?

A

low; 10% (one head of the myosin molecule is only bound for about 10% of the ATPase cycle)

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22
Q

How many heads does myosin II have? How many heads does myosin V have?

A

20 heads; 2 heads

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23
Q

myosin V is an (blank) motor, while myosin II drives (blank)

A

organelle; muscle contraction

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24
Q

It takes (blank) myosin II molecules to propel an actin filament

A

many

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25
Q

In muscle, how are myosin II molecules assembled? The filaments form by association of (blank) regions of the tail. What is the area called where the tails overlap?

A

In muscle, myosin II molecules are assembled into a thick filament; hydrophobic; bare zone

26
Q

What is the fundamental contractile unit in muscle?

A

muscle sarcomere

27
Q

When does the sarcomere contract?

A

when myosin thick filaments and actin thin filaments slide past each other

28
Q

What accessory proteins of actin keep the actin filament a constant length?

A

Cap Z and tropomodulin

29
Q

What accessory proteins does the Z disc contain to stably join sarcomeres?

A

alpha-actinin and other proteins

30
Q

What accessory protein maintains thick filament position in the sarcomere?

A

titin

31
Q

What accessory protein sets the length of the thin filaments?

A

nebulin

32
Q

What types of muscles are regulated via the thin filament? What types of muscles are regulated via the thick filament?

A

skeletal and cardiac; smooth

33
Q

How is smooth muscle regulated?

A

Myosin (thick filament) becomes phosphorylated by myosin light chain kinase and becomes activated. MLCK is activated by calcium binding to calmodulin

34
Q

How are skeletal and cardiac muscle regulated?

A

Tropomyosin wraps around the actin filament and blocks the myosin binding sites. When Ca+ binds to Troponin C, it moves tropomyosin out of the way of the myosin binding sites.

35
Q

What wraps around actin filaments blocking myosin binding sites on actin?
What does Calcium bind to in order for tropomyosin movement away from myosin binding sites.

A

tropomyosin; troponin C

36
Q

With an increase in myoplasmic Ca+, what happens to the force of ATPase activity?

A

more Ca+ leads to more binding to troponin C, which moves the tropomyosin and allows for binding of myosin and more contraction

37
Q

Five factors that affect muscles ability to generate force and contract

A

Myosin isoforms
Frequency of stimulation
Number of motor units stimulated.
Degree of stretch (Frank-Starling relationship).
Whether muscle is allowed to shorten (Force-velocity relationship)

38
Q

What are the three phases of a muscle twitch?

A

latent period; contraction; relaxation

39
Q

How does decreasing the interval between stimuli affect the height of the second contraction? Why?

A

second peak will be higher than the first; additional influx of Ca+

40
Q

What are three things that will occur if you increase the frequency of stimulation of a muscle.

A

temporal summation –> complete tetanus –> fatigue

41
Q

What is this: When more stimuli are applied, more calcium is released

A

temporal summation

42
Q

What is this: When muscle is generating maximal force, and all sites on troponin C are occupied.

A

complete tetanus

43
Q

Asynchronous motor-unit activity (motor unit A, motor unit B, motor unit C) maintains a nearly constant tension in the total muscle. What does this mean?

A

Different motor units are firing at different times, but when you add them up, they result in a fairly constant muscle tension.

44
Q

What is this: a motor neuron and all of the muscle cells it stimulates

A

motor unit

45
Q

When a stronger contraction is needed, the nervous system stimulates more (blank)

A

motor units

46
Q

What is this: the stimulation of additional motor units for increased strength of contraction

A

recruitment

47
Q

The number of motor units that are recruited is determined by the number of (blank) that are stimulated by the central nervous system

A

motor neurons

48
Q

By varying the number and size of recruited (blank), the nervous system can control the degree of contraction of a particular muscle

A

motor units

49
Q

In addition to the frequency of stimulation and the number of motor units recruited, the strength of a muscle contraction can also be altered by changing the starting length of a muscle. What is this called?

A

length-tension relationship

50
Q

There is an “optimal” stretching length in a sarcomere that provides the greatest tension and thus the greatest force of contraction. What is this mechanism?

A

Frank-Starling

51
Q

There is a change in the isotonic twitch response of a muscle fiber with different loads. Does the muscle shorten a greater distance with a light load or a heavy load? Does it shorten quicker with a light load or a heavy load?

A

light load; light load

52
Q

How are shortening velocity and load related?

A

With a lighter load, greater shortening velocity

53
Q

What percentage of proteins in the body are myosins? What to myosin mutations lead to?

A

10-15%; muscle disorders

54
Q

What does a mutation in myosin heavy chain IIa cause?

A

muscle myopathy

55
Q

What’s this?
Clinical Features: Muscle Weakness. Atrophy near shoulders, back, hand and thigh muscles
Pathogenesis: Mutations primarily to SH1 Helix in myosin. Thought to alter actin-myosin ATPase activity

A

muscle myopathy

56
Q

What is this caused by?
Disease: Distal arthrogryposis. Freeman-Sheldon Syndrome, Sheldon-Hall Syndrome.

Clinical Features: Joint contractures with predominant distal involvement.

Pathogenesis: Mutations in troponin I, troponin T, tropomyosin, perinatal myosin and embryonic myosin. Thought to disrupt sarcomere development.

A

mutations to embryonic MyHC

57
Q

What is this caused by?
Disease: Laing myopathy.

Clinical Features: Weakness of ankle dorsiflexion and “hanging big toe”.

Pathogenesis: Mutations are in the LMM region of
Myosin. Thought to disrupt myosin filament formation or disrupt interactions with myosin binding proteins like titin.

A

mutations to B-Cardiac myosin

58
Q

What are point mutations to B-cardiac myosin, actin, troponin, and tropomyosin linked to?

A

familial hypertrophic cardiomyopathy (FHC) and dilated cardiomyopathy (DCM)

59
Q

Mutations in myosin can cause (blank) and sudden death

A

familial hypertrophic cardiomyopathy

60
Q

(blank) mutations enhance myosin force generation

(blank) mutations decrease myosin force generation

A

FHC; DCM

Block 4 Week 1 Meg (13 decks)

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