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Exercise Biochemistry > Structure of Muscle and Enzymology > Flashcards

Structure of Muscle and Enzymology Flashcards

1
Q

What percentage of muscle is skeletal?

A

30-40

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2
Q

What is the function of skeletal muscle?

A

Attached to bones to provide posture and movement

Contributes to temperature control

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3
Q

What is the organisation of muscle filaments?

A

myofibril
Fibre
fasicule/bundle
muscle

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4
Q

What/where are the connective tissue layers?

A

Endomysium around fibres
Perimysium around bundles
Epimysium around muscle

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5
Q

Which level of muscle organisation contains blood vessels?

A

Bundles

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6
Q

What is the structure of fibres?

A

Multinucleate cells with 1 nucleus per 30µm

10-100µm diameter

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7
Q

What diameter are myofibrils?

A

1-3µm

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8
Q

What length is overall muscle?

A

> 300mm

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9
Q

What length is the sarcomere?

A

2-3µm

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10
Q

What is the ratio of M:A in a sarcomere?

A

2:1

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11
Q

How many myosin types are there?

A

12 classes

38 genes

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12
Q

What is the main myosin in contraction?

A

2

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13
Q

What is the structure of the myosir filaments?

A

Antiparallel myosin proteins

  1. 3nm axial repeat
  2. 9 helical repeat
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14
Q

What is the structure of a myosin dimer?

A

N terminal head
4 Light chains
155nm coiled heavy chain tail

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15
Q

What does titin bind?

A

Links myosin tail to Z disc

Spans half of sarcomere

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16
Q

What function does Titin have?

A

Provides 90-95% of elastic/passive force

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17
Q

What is the structure of a myosin head?

A 
NBD
U50
actin/cardiomyopathy loop
L50
Relay helix with kink
converter α helix
lever arm
regulatory and essential light chains
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18
Q

What is the structure of the actin filament?

A

Left helix
72nm pitch
5.5nm G-actin subunit repeat
4-7nm diameter

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19
Q

Where does the actin anchor to?

A

+ /fast growing end

α-actinin in Z disc

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20
Q

What does nebulin do?

A

Binds actin to regulate filament length

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21
Q

How frequently does tropomyosin bind to actin?

A

1 per 7 actin subunits

22
Q

What is the troponin complex that binds Calcium?

A

TnC

23
Q

Is all troponin calcium binding equal?

A

No! Different isoforms

24
Q

What does tropomyosin do?

A

Binds in F-actin grooves to occlude the binding site f the myosin head

25
Q

What is the structure of the the troponin-tropomyosin complex?

A 
Actin
TnI
TnC
TnT
Tropomysoin
26
Q

Outline the excitation contraction coupling?

A

Impulse arrives at motor end plate and passes across the synapse to the sarcolemma
Diffuses to T tubule to span into myofibrils
Conformational change in v-gated Dihydropyridine receptor transducted to RyR ER Calcium channel
Ca released into myofibrillar space to [10µM]
Ca binds to TonC
Conformational change removes tropomyosin
Myosin binds

27
Q

How is the ER calcium store maintained?

A

Calsequestrin buffer proteins

SERCA ATPase pump

28
Q

Is the cross bridge response immediate?

A

No, delay for exposure of binding sites

29
Q

Is the cross bridge response uniform?

A

No, more binding sites exposed with [Ca]

30
Q

What are the 3 types of fasicules?

A

parallel
unipinnate
bipinnate

31
Q

What characteristics do parallel fasicules have?

A

Faster

greater range

32
Q

What characteristics do pinnate fasicules have?

A

Larger area

Stronger

33
Q

What is the equation for force?

A

F=(Vσ)/length

34
Q

Where are tendons in bipinnate muscles?

A

Intramuscular

35
Q

How fast is ATP hydrolysis in muscle?

A

10^9 faster than normal

36
Q

How many ATP are hydrolysed per second?

A

4

37
Q

What is Mg needed for in muscle?

A

Coordination of 4 Water and Phosphates of ATP

38
Q

What is the structure of the ATP binding site in myosin?

A

P loop locks ATP in the active site

S/T residues coordinate H2O

39
Q

How does ATP hydrolysis prime myosin to bind to actin?

A

Relaxes the P loop
By rotation of myosin
Allows stronger binding of actin to the cardiomyopathy loop upon tropomyosin removal

40
Q

What phase of the cross bridge cycle has a straight relay helix?

A

Actin-Myosin

41
Q

What drives the powerstroke?

A

Release of phosphate

42
Q

What distance does the myosin head move in the power stroke?

A

12nm

43
Q

How does ATP binding act in the cross bridge cycle?

A

Closure of P loop
Bends relay helix
Induces stress in conformation (high energy state)

44
Q

When does ATP hydrolysis occur in the cross bridge cycle?

A

When detached

45
Q

What form is most myosin in the cross bridge cycle?

A

ATP/ADP+Pi bound

Detached from actin

46
Q

What stage of the actin-myosin cycle has tightest binding?

A

Straight relay helix of A.M

47
Q

How many actin subunits bind per myosin head?

A

5

48
Q

What residues control the relay helix kink?

A

Hydrophobic

49
Q

How much energy does ATP hydrolysis provide?

A

-60kJ/mol

50
Q

How much force does 1 Joule provide?

A

1N/m

51
Q

How efficient is myosin ATPase?

A

60%

Exercise Biochemistry (4 decks)

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