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Human Physiology and Pharmacology > Week 13: (B) Coupling and Skeletal Muscle Contraction > Flashcards

Week 13: (B) Coupling and Skeletal Muscle Contraction Flashcards

1
Q

What are the 3 proteins of the thin filament?

A

Troponin, Actin, Tropomysosin

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2
Q

what are the 3 types of Troponin?

A

Troponin T, I & C

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3
Q

what does Troponin T do?

A

binds to trypomyosin-

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4
Q

What does Troponin I do?

A

bind to actin inhibit contraction

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5
Q

What does Troponin C do?

A

binds to Ca+

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6
Q

Structure of Actin?

A

double stranded alpha-helical

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7
Q

Does actin have a binding site?

A

BS for attachment with myosin cross bridge

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8
Q

What happens to troponin when NOT bound to Ca+?

A

stabilises tropomyosin in its blocking position over the actin cross bridge BS.

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9
Q

Tropomyosin structure?

A

2 stranded helixes wrap around each other to form a ribbon, this wraps around the actin and the troponin attached to this

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10
Q

What chains are present in thick filaments?

A

2 heavy chains, 2 regulatory light chains, 2 chains alkali chains.

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11
Q

What does the Alkali light chain do on the myosin head region?

A

stabilises head region

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12
Q

What does the regulatory light chain do on the myosin head?

A

Regulates ATPase activity of myosin

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13
Q

What regulates ATPase activity of myosin?

A

RLC which is in turn regulated by phosphorylation by kinase

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14
Q

what does the heavy chain do on the head region of myosin?

A

binding site for actin

binding and hydrolysing ATP

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15
Q

what can the heavy head region also be called?

A

S1

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16
Q

What do the heads of myosin form?

A

cross-bridge

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17
Q

what type of myosin attached to actin?

A

Myosin-ii

18
Q

what is step 1 of a muscle contraction?

A

myosin-ii heads bind to actin, cross-bridge becomes distorted, myosin heads detach from myosin

19
Q

What happens to ATP for myosin heads to move away?

A

Hydrolysis of ATP

20
Q

How is a muscle contraction triggered?

A

increase Ca2+ concentration

21
Q

What does increased Ca2+ concentration do?

A

removes inhibition of cross bridge cycling

22
Q

How does Ca2+ modulate contractions?

A

regulatory proteins act together to inhibit myosin and actin interactions

23
Q

What does Ca+ bind to to stimulate a contraction?

A

Troponin C. release inhibition of Troponin I (bound to actin to block cross-bridge)

24
Q

Where does ATP bind on Myosin?

A

Heavy chain

25
Q

What happens when ATP is bound to Myosin? (pt 1)

A

Reduce affinity for actin, detachment

26
Q

How is a muscle cell relaxed?

A

ATP bound to Myosin

27
Q

What happens when hydrolysis of ATP on myosin occurs? (pt 2)

A

Remains on the myosin, myosin swings back.
cocked state
lines up with a new actin monomer

28
Q

When is the muscle relaxed?

A

ATP is bound, Myosin head swings back

29
Q

when will the cross-bridge form?

A

If intracellular Ca2+ concentrations are high enough

30
Q

What happens to ADP + Pi when cross-bridge is formed?

A

inorganic phosphate released, triggers power stroke

31
Q

What happens in the power stroke?

A

Myosin head confo change, move ~45 degrees about the hinge, pulls actin towards tail of myosin

32
Q

what happens after the power stroke?

A

ADP is released, myosin complex left in a rigid state.

33
Q

How can the myosin-actin complex be relaxed?

A

ATP binding to heavy chain on head of myosin= relaxed

34
Q

Do the thin of thick filaments move when contracting?

A

Thin slide over thick

35
Q

Does the sarcomere shorten?

A

YES as thin filaments move closer together

36
Q

Does the A band change width?

A

no, stays the same width

37
Q

does the I band width decrease?

A

Yes, don’t overlap thick so shorten

38
Q

does the H zone decrease?

A

Yes, similarly to the M line

39
Q

Does the Z line decrease?

A

Yes, distance between decrease

40
Q

What happens in riggor mortis?

A

Ca2+ rise (starts around 3-4hrs after death, complete in 12hrs)
Allow actin to bind to myosin
No ATP produced from the death body so stuck in rigid state

41
Q

what happens when Ca2+ binds to Troponin on tropomyosin?

A

Binds to Troponin C to remove the blocking Troponin I by shifting it to expose the Myosin binding site.
Also TnT moved away from binding site into a groove

Human Physiology and Pharmacology (31 decks)

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