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템 > Contractile Proteins and Muscle Diseases > Flashcards

Contractile Proteins and Muscle Diseases Flashcards

1
Q

Describe the electron micrograph of a single myosin molecule

A

Two-headed structure with a long, thin tail

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2
Q

What are the thick and thin filaments associated with the contractile apparatus in skeletal muscle?

A

Thin filaments = actin

Thick filaments = myosin

Actin are anchored by Z-discs; 6 thin filaments surround each end of 1 thin filament

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3
Q

Describe the bipolar assembly of myosin

A

Bipolar assembly refers to self-assembly at the tails.

Myosin filaments arranged with tails facing each other (middle = bare zone), tails are coiled coil of 2 alpha helices, light chains and N terminus located near heads at hinge region

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4
Q

_______ makes up 35% of total protein in muscle cells

A

Myosin

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5
Q

Myosin is made up of ____ polypeptide chains:

_____ heavy chains + ______ light chains

It has a _______ rod domain and _____ globular heads

A

6

2; 4

Helical; 2

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6
Q

Which region of myosin hydrolyzes ATP

A

Head region

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7
Q

The myosin heads are at _____ degrees rotational symmetry and the surrounding thin filaments are at _____ degrees rotational symmetry

A

30; 60

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8
Q

Treatment of muscle myosin with proteases like _______ or ________ creates stable fragments

A

Papain; trypsin

[papain cleaves at hinge region, trypsin further down the tail]

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9
Q

The myosin tails are arranged in a coiled-coil formation, and with every turn you have _________ residues interacting

A

Hydrophobic

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10
Q

The structure of the S1 fragment (head and neck region) of myosin exhibits a _______ ______ domain

A

P-loop ATPase

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11
Q

The structure of the S1 fragment (head and neck region) of myosin exhibits a P-loop ATPase domain. The P-loop serves as the ______ binding site, while the _______ binding site is closer to the head

A

Nucleotide; actin

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12
Q

The structure of the S1 fragment (head and neck region) of myosin exhibits a P-loop ATPase domain. What 2 types of light chains are associated with the neck region?

A

Essential light chain

Regulatory light chain

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13
Q

Part of the myosin molecule moves dramatically (essential light chain and regulatory light chain in neck region) in response to what?

What is the significance of this?

A

ATP binding, hydrolysis, and product release

This is what propels myosin along an actin filament!

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14
Q

What region of the sarcomere corresponds to actin filaments only?

A

I band

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15
Q

What region of the sarcomere contains both myosin and actin?

A

A band

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16
Q

What protein is responsible for anchoring actin filaments at the ends of each sarcomere?

A

Z-disc

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17
Q

What protein is responsible for anchoring myosin to portions of the z disc?

A

Titin

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18
Q

What protein links the bipolar assembly of myosin together?

A

Myomesin 1 (aka M protein)

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19
Q

Characterize the directionality of actin

A

Minus end = pointed end

Plus end = barbed end - this is what sticks to the z-disc

20
Q

_______-actin assembles into _______-actin (or filamentous actin), which exists in a ______ ______ arrangement with 2 parallel strands that twist around each other.

A

G; F; double helical

21
Q

Each G-actin monomer interacts with ____ neighbors. The growing and the final filament exhibits directionality (plus and minus end).

ATP binds ____ G-actin first. The mature filament contains _______ bound to the monomeric G-actin units

A

Four

Free; ADP

22
Q

Which end of actin attaches to the z-disc?

A

Plus end (barbed end)

23
Q

The size and position of the actin filament is controlled by several proteins.

_______ caps the minus end (not at Z-disc), preventing further polymerization

A

Tropomodulin

24
Q

The size and position of the actin filament is controlled by several proteins.

_________ (or beta-actinin, a heterodimer), which associates with alpha-actinin, caps at the plus end

A

CapZ

25
Q

The size and position of the actin filament is controlled by several proteins.

_______ (6,669 residues): “ruler” and template for actin polymerization

A

Nebulin

26
Q

____________ binds tropomyosin; positions the complex on the filament

A

Troponin T

27
Q

__________ binds actin; inhibits myosin binding

A

Troponin I

28
Q

_________ binds Ca and relieves inhibition

A

Troponin C

29
Q

What protein assists in formation of contractile bundle at Z disc - forming bridges between adjacent thin filaments?

A

Alpha-actinin

30
Q

Indirect immunofluorescence micrographs of isolated sheets of skeletal muscle Z discs using antibodies to alpha-actinin show that it occurs at the _______ of the Z disc

_______ protein is distributed about the Z-disc periphery

A

Interior

Desmin

31
Q

Dystrophin is a 2400 kb gene with 3685 amino acid residues and 79 exons. There are numerous isoforms. What accounts for C-termini vs. N-termini variability?

A

C-termini variability: Alternative exon splicing

N-termini variability: Alternative transcription initiation sites

32
Q

Dystrophin is in the same protein family as what other 2 important proteins?

A

Alpha-actinin

Spectrin

33
Q

Duchenne Muscular Dystrophy and Becker Muscular Dystrophy result from what genetic event?

A

Exon deletions (may also be exon duplications but that is less common)

34
Q

What is the difference between DMD and BMD?

A

Duchenne muscular dystrophy - no detectable dystrophin

Becker muscular dystrophy - dystrophins of various sizes

35
Q

What is the inheritance pattern for DMD?

A

X-linked recessive

36
Q

What is the role of dystrophin in the musculoskeletal system?

A

Dystrophin is a 427 kDa rod-like protein that connects the cytoskeleton to the basal lamina and stabilizes the membranes and participates in calcium handling

It is the largest human gene known

37
Q

What mediates the conversion of glycogen to glucose in muscle cells?

A

Glycogen phosphorylase

38
Q

What mediates the conversion of glucose to pyruvate in muscle cells?

A

AMP

39
Q

Activation of muscle glycogen phosphorylase occurs by ______ and by phosphorylation. Muscle glycogen phosphorylase is composed of _____ identical subunits.

AMP binds to the ________ site, a site separate from the active catalytic site.

_________ ________ can phosphorylate a specific serine residue on each subunit. Either phosphorylation or binding of AMP causes a change in the active site that increases the activity of the enzyme

A

AMP; two

Allosteric

Phosphorylase kinase

40
Q

In Tarui disease (glycogen storage disease VII), the muscle isoform of the rate limiting enzyme of glycolysis is defective. This enzyme is subject to allosteric control; it is activated by some and inhibited by other modulatos. To make a definitive diagnosis of Tarui disease, the activity of this enzyme in muscle biopsies needs to be measured. Because the amount of tissue in a biopsy is very small, the assay needs to be as sensitive as possible (i.e., all activating), but none of the inhibiting modulators should be present. Which of the following inhibits the enzyme and should be left out of the assay mixture?

A. ADP
B. AMP
C. Citrate
D. Fructose-6-Phosphate

A

C. Citrate

41
Q

What enzyme is deficient in Tarui disease? What tissue does this disease affect?

A

PFK

Affects muscle tissue

42
Q

What are the clinical features of Tarui disease, and what disease are its symptoms similar to?

A

Clinical features: exercise intolerance, muscle cramping, exertional myopathy, compensated hemolysis, and myoglobinuria

Symptoms can be similar to McArdle’s Glycogen Storage Disease, but more severe

43
Q

A 25 y/o african american male notices increased fatigue and decreased performance when playing outfield for his office softball team. After a game in hot weather with many fielding chances, he has severe muscle pains and cramps that keep him awake and he notices that his urine is dark that night. His physician suspects McArdle disease (type V glycogen storage disease) and has him run on a treadmill breathing air with reduced oxygen. The man develops severe cramps after this ischemic exercise, further supporting the presumptive diagnosis. A diagnostic muscle biopsy is likely to show which of the following?

A. Increased normal glycogen with a deficient hexokinase
B. Increased normal glycogen with a deficient glycogen synthase
C. Increased normal glycogen with a deficient phosphorylase
D. Decreased muscle glycogen with decreased glycogen synthase
E. Decreased muscle glycogen with decreased debranching enzyme

A

C. Increased normal glycogen with deficient phosphorylase

44
Q

What are the 3 possible fates of glucose 6-phosphate?

A
  1. Used as fuel for anaerobic or aerobic metabolism (fed into glycolysis)
  2. Converted into free glucose in the liver and then released into blood (using glucose 6 phosphatase)
  3. Processed by pentose phosphate pathway to generate NADPH or ribose
45
Q

__________ from the adrenal medulla enhances glycogen breakdown in muscle and liver to provide fuel for muscle contraction

A

Epinephrine

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