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MCB1 Block 3 > Muscle Contraction > Flashcards

Muscle Contraction Flashcards

1
Q

What is the contractile unit of a muscle cell?

A

sarcomere

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2
Q

Hundreds of what form the thick filament of the myofibril

A

myosin II (motor protein)

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3
Q

Describe the structure of myosin II

A

2 ATPase heads

heavy chain tail

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4
Q

Describe how the myosin II arrange themselves on the actin filaments

A

tails face the middle (bare zone or M line), heads protrude out in both directions

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5
Q

What covers up the myosin binding sites on actin thin filaments?

A

tropomyosin (with troponin bound to it)

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6
Q

When calcium is released, where does it bind to initiate muscle contraction?

A

troponin

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7
Q

The location where tails of thick filaments are embedded is called:

A

M line

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8
Q

What is a sarcomere?

A

One Z line to next Z line

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9
Q

What is brought closer together during muscle contraction?

A

Z lines

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10
Q

What is the structure of a thin filament?

A

double helix of actin monomers, tropomyosin wound around it.

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11
Q

In an electron micrograph the dark line in the middle of the white section is what?

A

Z disk

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12
Q

What contracting in muscle cell?

A

myofibril

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13
Q

In the sarcomere, F-actin is often ____

A

capped

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14
Q

What caps the positive end of F-actin in sarcomere?

A

Cap Z

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15
Q

What caps the - end of F-actin in sarcomere?

A

Tropomodulin

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16
Q

Describe muscle contraction

A

Nerve signal triggers action potential in muscle cell membrane, spreads into T-tubules (membrane invaginations), then across gap junctions to sarcoplasmic reticulum
→ release of Ca2+

Ca2+ binds troponin C, lifts troponin I from actin
→ displaces tropomyosin

Myosin head can now bind

“walks” forward. Sliding model. POWER STROKE

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17
Q

What is the sarcolemma?

A

plasma membrane of muscle cell

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18
Q

What is the sarcoplasmic reticulum?

A

specialized sER for calicium storage in muscle cells

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19
Q

Myofibrils are made of overlapping:

A

thick and thin filaments

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20
Q

What two things are needed for contraction of muscle cell

A

calcium, ATP

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21
Q

What is required to release the myosin head from actin thin filament?

A

ATP

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22
Q

Describe the power stroke, or the steps involved in myosin heads walking along actin in muscle contraction

A

calcium - troponin leaves trypomyosin so myosin heads can bind
ATP causes release of a head
hydrolysis - ADP
myosin head moves forward and binds, pulling sarcomere closer together

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23
Q

What is the driving force behind the myosin power stroke?

A

ATP hydrolysis

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24
Q

Myosin walks toward where?

A

+ end of actin

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25
Q

Explain rigor mortis

A

No ATP so myosin can’t release from actin

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26
Q

Key words: mutation where actin binds Z disk, early heart failure is what disease?

A

Dilated cardiomyopathy

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27
Q

Symptoms of CHF develop gradually; dyspnea, weakness, fatigue, palpitations, ankle edema; risk of PE and sudden death is what disease?

A

Dilated cardiomyopthy

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28
Q

What is the mode of inheritance for dilated cardiomyopathy?

A

30% is hereditary

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29
Q

Describe the mechanism for dilated cardiomyopthy

A

Mutated actin where it binds to Z disk → defective transmission of force in cardiac myocytes → early heart failure

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30
Q

Where is the defect in dilated cardiomyopthy?

A

Mutated cardiac isoform of actin where binds to Z disk

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31
Q

What is the spring like protein that anchors thick filaments into z disk?

A

titin

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32
Q

What is the most commonly mutated protein found in dilated cardiomyopthy?

A

Titin

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33
Q

Key words: angina, fatigue, main cause for sudden cardiac death in athletes is what disease?

A

Familial Hypertrophic Cardiomyopathy

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34
Q

Characteristics: asymptomatic/mild symptomatic; dynspnea, angina, palpitation, syncope, fatigue, fatal cardiac arrest (5-10%); #1 cause for sudden cardiac death in athletes is what disease?

A

Familial Hypertrophic Cardiomyopathy

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35
Q

What is the mechanism for Familial hypertrophic cardiomyopathy?

A

Defective cell migration

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36
Q

What is the mode of inheritance for familial hypertophic cardiomyopathy?

A

AD

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37
Q

Where is the defect in familial hypertrophic cardiomyopathy?

A

Myosin II motor protein (70%), tropomyosin, troponin

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38
Q

What is the name of one muscle cell?

A

myofibril

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39
Q

Each myofibril is composed of many

A

sarcomeres

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40
Q

What is the function of dystrophin?

A

Helps keep shape of muscle cell membrane. Helps transport force from muscle contraction to ECM

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41
Q

Describe the shape of dystrophin

A

very long and straight

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42
Q

What is dystrophin attached to (GENERALLY)?

A

Actin-cytoskeleton & integral membrane glycoprotein complex

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43
Q

What does the integral membrane glycoprotein complex that dystrophin attaches to interact with?

A

ECM (laminin, collagen)

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44
Q

What specific things is dystrophin attached to?

A

actin, dystroglycans, synaptrohins, dystrobrevin

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45
Q

Dystrophin helps link the actin cytoskeleton to what?

A

laminin-2

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46
Q

Beta dystroglycan binds to what?

A

dystrophin & alpha dystroglycan, GRB2

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47
Q

What does alpha dystroglycan bind?

A

ECM, glycoprotein (laminin), proteoglycan (agrin)

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48
Q

What is the function of the sarcoglycan complex?

A

help with binding & recruitment of alpha dystroglycan, they are very important for structural stability of whole protein complex

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49
Q

Absence of dystrophin means what?

A

loss of DAP at sarcolemma (DAP is dystrophin associated protein) → absence of physical link → fragile sarcolemma

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50
Q

If a person doesn’t have dystrophin what happens with repeated movement?

A

muscle degeneration

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51
Q

What is the name of the cell that performs the majority of muscle repairs and regeneration?

A

satellite cells

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52
Q

Where are satellite cells located?

A

in basal lamina that surrounds every cell

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53
Q

What activates satellite cells?

A

stress or trauma

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54
Q

What kind of division do satellite cells undergo?

A

asymmetric division

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55
Q

Explain the asymmetric division that satellite cells do when they divide?

A

they divide into another satellite cell & into a myoblast

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56
Q

Stem cells (side population cells) differentiate into what?

A

haematopoetic cells & satellite cells

57
Q

What gives rise to a new myoblast?

A

satellite cell

58
Q

In MD, why is there CT and fat accumulation?

A

The stem cells cannot keep up with the demands of all the damaged muscle cells. Satellite cells have telomeres with a certain length so they only have so much dividing capability, MD wears them out

59
Q

List the 3 steps absence of dystrophin will do to a cell

A

↑ susceptibility to contraction-induced injury

Repeated degeneration-regeneration & ongoing inflammation & necrosis

Eventual muscle destruction

60
Q

The earlier the age of onset, the:

A

faster the progression

61
Q

What is an enzyme found inside muscle cells that is involved with storage of ATP in cells?

A

serum creatine kinase

62
Q

key words: onset of muscular weakness at 3-5 y/o, mild cognitive impairment, absence of dystrophin, pseudohypertrophy is what disease?

A

Duchenne Muscular Dystrophy

63
Q

what does DMD stand for?

A

Duchenne Muscular Dystrophy

64
Q

Characteristics: Most common & most severe MD; progressive; normal at birth, onset muscle weakness at 3-5 y/o, gower’s sign, calf psuedohypertrophy (insufficient repair response of satellite cells causes accumulation of CT & fat), lordosis & scoliosis, contractures, mild cognitive impairment, respiratory & cardiac musculature impairment; pelvic girdle muscles ! shoulder girdle muscles; wheelchair bound by 10-12 y/o; rare survival beyond 20-30 years; most death due to respiratory or cardiac failure is what disease?

A

Duchenne Muscular Dystrophy

65
Q

What is the mode of inheritance for Duchenne Muscular Dystrophy?

A

X linked (2/3 from carrier mother, 1/3 new mutation)

66
Q

What is mechanism for Duchenne Muscular Dystophy?

A

Mutation causes complete absence of dystrophin in muscle → loss of DAP at sarcolemma & fragile sarcolemma → increased susceptibility to contraction-induced injury → repeated degeneration-regeneration & ongoing inflammation & necrosis → eventual muscle destruction; progressive muscular weakness & atrophy → increase serum creatine kinase

67
Q

Where is the defect in Duchenne Muscular Dystrophy?

A

Xp21 dystrophin mutation – complete absence of dystrophin (frameshift insertion/deletion, partial deletion, point mutation)

68
Q

Most of the time the deletion in DMD is what kind?

A

frameshift

69
Q

Which is the most common and most severe degenerative skeletal & cardiac muscle disorder?

A

DMD

70
Q

What is the second largest known gene?

A

dystrophin

71
Q

What disease does dystrophin partly function?

A

BMD

72
Q

How many exons are in the dystrophin gene?

A

79

73
Q

How many promoters are in the dystrophin gene?

A

7

74
Q

Why is there a high incidence of mutation in dystrophin gene?

A

There is a lot of Interspersed intronic repetitive sequences

75
Q

In BMD there can be variable what?

A

symptoms

76
Q

Why does a pt with DMD have calf pseudohypertrophy?

A

Looks like pt has massive calf muscle. Its enlarged b/c of repeated degeneration and accumulation of muscle tissue and fat.

77
Q

The majority of pts with DMD end up dying from what?

A

respiratory failure

78
Q

what percentage of pts with DMD die from repiratory failure?

A

70%

79
Q

If a pt with DMD doesn’t die from respiratory failure, they are probably going to die from what?

A

cardiac failure

80
Q

What is the purpose of checking the serum creatine kinase levels if you suspect a pt has MD?

A

will tell you if there’s cell rupture

81
Q

If you suspect pt has MD you can run western blot with what kind of antibody?

A

dystrophin

82
Q

Describe the western blot of a normal person vs. a pt with DMD or BMD

A

DMD won’t have any lines b/c they don’t have any dystrophin. BMB extra lines and in different location - they have abnormal dystrophin.

83
Q

Why is spectrin used when running a western blot for dystrophin?

A

It is used as a control to make sure protein has actually been extracted from the tissue.

84
Q

What can be used to confirm a pt has DMD?

A

PCR deletion screen

85
Q

Explain how PCR deletion screen can confirm DMD

A

Conformation of diagnosis, 18 exons out of 79 exons account for about 98% of deletions we find. So you will do PCR to flank the 18 exons that are usually deleted.

86
Q

If a women is carrier for DMD will she show symptoms?

A

Usually not

87
Q

What percentage of women carriers of DMD will show symptoms?

A

8%

88
Q

What are women carriers who show symptoms of DMD called?

A

manifesting heterozygotes

89
Q

Why will women who are carriers for DMD show symptoms?

A

random x-chromosome inactivation

90
Q

Key words: dystrophin mutation, late childhood onset, variability are what disease?

A

Becker Muscular Dystrophy

91
Q

What does BMD stand for?

A

Becker Muscular Dystrophy

92
Q

Characteristics: Onset late childhood/adolescence, slower progression than DMD, significant variability of symptoms determined by type of mutation in gene stand for what disease?

A

BMD

93
Q

What is the mechanism for Becker Muscular Dystrophy?

A

Mutated dystrophin → aberrant but partially function dystrophin protein (milder disease form); progressive muscular weakness & atrophy → increase serum creatine kinase

94
Q

What is the mode of inheritance for BMD?

A

X-linked

95
Q

Where is the defect in BMD?

A

Mutation in dystrophin – presence of protein but mutated (inframe insertion/deletion

96
Q

How has BMD helped find treatments for pts with DMD?

A

Has allowed us to see what deletions are survivable and what part of dystrophin gene is necessary. Has helped scientists find “important” dystrophin domains. Has allowed them to make a mini dystrophin that can be cloned into cells for gene therapy

97
Q

Key words: emerin, sudden cardiac or respiratory failure are what disease?

A

Emery-Dreifuss Muscular Dystrophy (EDMD)

98
Q

What does EDMD stand for?

A

Emery-Dreifuss Muscular Dystrophy

99
Q

Characteristics: Onset early childhood, early contractures (elbows, ankles, neck) – flexion deformity of elbows & reduced joint mobility; slowly progressive muscle weakness & atrophy; upper arms & lower legs ! shoulder & hips; cardiomyopathy, conduction defects, & arrhythmias are what disease?

A

EDMD

100
Q

What is the mechanism for Emery-dreifuss MD?

A

Defects in lamin (IF) assembly/attachment to nuclear envelope → fragile NE → affects physically stressed tissues, particularly muscle fibers

101
Q

What is the mode of inheritance for EDMD if defect is in emerin?

A

X-linked

102
Q

What is mode of inheritance for EDMD if defect is in lamin A/C?

A

AD or AR

103
Q

Where is the defect in EDMD?

A

Mutation in Emerin (X-linked); Lamin A/C (autosomal dominant/recessive, rare)

104
Q

Key words: myotonin protein kinase, CTG repeat disorder, anticipation, multisystemic, slowly progressive
are what disease?

A

Myotonic Dystrophy

105
Q

Characteristics: Common; multisystemic disorder; onset 20-40 y/o (any age birth to old age); myotonia = sustained involuntary contraction of muscle group; weakness: hands, legs (gait abnormalities), SCM; atrophy of fascial muscles → ptosis & haggard appearance are what disease?

A

Myotonic Dystrophy

106
Q

What is the mechanism for myotonic dystrophy?

A

Pathogenesis not well understood; anticipation – with each successive generation, the repeat disorder expands causing increase in severity of mutation/symptoms each other generation

107
Q

What is the mode of inheritance for myotonic dystrophy?

A

AD

108
Q

Where is the defect in myotonic dystrophy?

A

Myotonin protein kinase; trinucleotide repeat disorder (CTG)

109
Q

If a pt has myotonin dystrophy, what will happen as the pt has offspring, and they have offspring, etc.?

A

More repeats every time the chromosome goes through a germline.

110
Q

Key words: expressionless, ptosis, normal life expectancy, winged scapula are what disease?

A

Facioscapulohumeral Muscular Dystrophy

111
Q

Characteristics: Rare; onset 10-40 years (95% by age 20); inability to puff cheeks; initial facial weakness (expressionless), ptosis; progressive weakness of face, scapula, & upper arms → difficulty raising arms → winged scapula are what disease?

A

Facioscapulohumeral Muscular Dystrophy

112
Q

What is the mechanism for Facioscapulohumeral Muscular Dystrophy ?

A

Not well understood

113
Q

What is the mode of inheritance for Facioscapulohumeral Muscular Dystrophy ?

A

AD

114
Q

Where is the defect for Facioscapulohumeral Muscular Dystrophy ?

A

Deletion of subtelomeric tandom repeat (4q35) or t4q;10q

115
Q

What are the two different kinds of limb girdle MD?

A

type 1 and type 2

116
Q

Which Limb girdle MD is more rare?

A

type 1

117
Q

key words: sarcoglycan mutation, no cognitive impairment, no pseudohypertrophy, no contractures are what disease?

A

Limb Girdle Muscular Dystrophy (LGMD 2)

118
Q

Characteristics: Weakness of proximal musculature; “limb girdle” – hip & shoulder; onset 10-20 years old; slower (& variable) rate of progression; severe disability within 20-25; death often from respiratory failure; pseudohypertrophy & contractures rare; no cognitive impairment are what disease?

A

Limb girdle muscular dystrophy 2

119
Q

What is the mechanism for limb girdle muscular dystrophy 2?

A

Defective assembly of sarcoglycans → disrupted interaction with dystroglycan protein complex → disrupted association of sarcolemma with ECM

120
Q

What is the mode of inheritance for limb girdle muscular dystrophy 2?

A

AR

121
Q

Where is the defect for Limb girdle MD 2?

A

Mutation (alpha-, beta-, gamma-, delta-) sarcoglycans

122
Q

What does LGMD stand for?

A

lamb girdle muscular dystrophy

123
Q

Is the heart affected in LGMD?

A

No

124
Q

Key words: onset at birth, laminin mutation, mental retardation is what disease?

A

Congenital Muscular Dystrophy

125
Q

Characteristics: General muscle weakness, respiratory insufficiency, contractures, seizures, mental retardation; clinically variable is what disease?

A

Congenital Muscular Dystrophy

126
Q

What is the mechanism for congenital muscular dystrophy?

A

Imparied myogenesis, synaptogenesis, & mechanical stability

127
Q

What is the mode of inheritance for Congenital muscular dystrophy?

A

congenital

128
Q

Where is the defect in congenital muscular dystrophy?

A

Mutation in laminin (of basal lamina)

129
Q

Where does laminin bind?

A

alpha dystroglycan of cell membrane.

130
Q

Are there any cures for MD?

A

No

131
Q

What is the general treatment for MD?

A

supportive: Physical therapy, pacemaker (EDMD & MD(

132
Q

Describe the myoblast transfer for treating DMD

A

inject donor muscle precursor cells into dystrophic host

133
Q

What are the challenges for gene therapy for DMD? (3)

A

Dystrophin gene too large for viral vectors

Many cells must contain the gene to improve muscle strength (muscle cells non-dividing)

Immune rejection of cells infected by vector

134
Q

Describe the clinical trial for stem cell therapy for treating DMD

A

multipotent pericyte-derived cells, from blood vessels of adult skeletal muscle (can differentiate into myoblasts → myotubes)
Systemic delivery of cells, genetically engineered to express mini-dystrophin
Navigate & differentiate into skeletal muscle

Take pts own cells and genetically enginerer them to express mini-dystrophin. Clone it into pts own cells, reinject cells back into pt, they will migrate to muscle damage and then will repair the damaged muscle, newly formed cells will express some dystrophin. By doing stem cell therapy pt will not be cured, but they will be changed from pt with DMD to a pt with milder like becker MD. Pts life will be radically improved.

135
Q

multipotent perycite derived cells can be triggered to differentiate into what?

A

satellite cells & other cells

136
Q

Where is utrophin expressed?

A

fetus

137
Q

Describe how upregulation of ultrophin can help treat DMD

A

Utrophin – expressed in fetus. Expression is shut off and dystrophin takes over. If they upregulate utrophin where dystrophin isn’t produced it can take on some function of dystrophin.

138
Q

Describe how Gene transfer & exon skipping

could help treat pts with DMD

A

Antisense oligonucleotide
Blocks exon spice sites to “skip” mutation/deletion
DMD → BMD

139
Q

Describe how the drug PTC124/Ataluren can help treat DMD

A

Pt has DMD has frameshift mutation in exon 4 – could design oligonucleotides that bind to exon donor and acceptor sites of exon 4 so that exon 4 is not spliced into the mature mRNA, so you skip over the exon that contains the mutation. So you don’t completely cure a pt, will convert pt with DMD to pt with a form of BMD.
Ataluren is in advanced trials. It would treat about 15% of cases with DMD and could also treat some CF. it’s a drug that inhibits nonsense-mediated RNA decay, so as ribosome complex goes over mRNA, normally if ribosome encounters premature stop codon, it stops translation. By binding of this drug to the ribosomal complex, it prevents ribosome from reading it as a stop codon. So it will read through it and translate the rest of the protein. The cases that are caused by premature stop codon could be cured by this drug.

MCB1 Block 3 (15 decks)

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