Structure of Muscle and Enzymology

Question 1

What percentage of muscle is skeletal?

Answer 1

30-40

Question 2

What is the function of skeletal muscle?

Answer 2

Attached to bones to provide posture and movement

Contributes to temperature control

Question 3

What is the organisation of muscle filaments?

Answer 3

myofibril
Fibre
fasicule/bundle
muscle

Question 4

What/where are the connective tissue layers?

Answer 4

Endomysium around fibres
Perimysium around bundles
Epimysium around muscle

Question 5

Which level of muscle organisation contains blood vessels?

Answer 5

Bundles

Question 6

What is the structure of fibres?

Answer 6

Multinucleate cells with 1 nucleus per 30µm

10-100µm diameter

Question 7

What diameter are myofibrils?

Answer 7

1-3µm

Question 8

What length is overall muscle?

Answer 8

> 300mm

Question 9

What length is the sarcomere?

Answer 9

2-3µm

Question 10

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

Answer 10

2:1

Question 11

How many myosin types are there?

Answer 11

12 classes

38 genes

Question 12

What is the main myosin in contraction?

Answer 12

2

Question 13

What is the structure of the myosir filaments?

Answer 13

Antiparallel myosin proteins

14. 3nm axial repeat
15. 9 helical repeat

Question 14

What is the structure of a myosin dimer?

Answer 14

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

Question 15

What does titin bind?

Answer 15

Links myosin tail to Z disc

Spans half of sarcomere

Question 16

What function does Titin have?

Answer 16

Provides 90-95% of elastic/passive force

Question 17

What is the structure of a myosin head?

Answer 17

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

Question 18

What is the structure of the actin filament?

Answer 18

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

Question 19

Where does the actin anchor to?

Answer 19

+ /fast growing end

α-actinin in Z disc

Question 20

What does nebulin do?

Answer 20

Binds actin to regulate filament length

Question 21

How frequently does tropomyosin bind to actin?

Answer 21

1 per 7 actin subunits

Question 22

What is the troponin complex that binds Calcium?

Answer 22

TnC

Question 23

Is all troponin calcium binding equal?

Answer 23

No! Different isoforms

Question 24

What does tropomyosin do?

Answer 24

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

Question 25

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

Answer 25

``` Actin TnI TnC TnT Tropomysoin ```

Question 26

Outline the excitation contraction coupling?

Answer 26

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

Question 27

How is the ER calcium store maintained?

Answer 27

Calsequestrin buffer proteins | SERCA ATPase pump

Question 28

Is the cross bridge response immediate?

Answer 28

No, delay for exposure of binding sites

Question 29

Is the cross bridge response uniform?

Answer 29

No, more binding sites exposed with [Ca]

Question 30

What are the 3 types of fasicules?

Answer 30

parallel unipinnate bipinnate

Question 31

What characteristics do parallel fasicules have?

Answer 31

Faster | greater range

Question 32

What characteristics do pinnate fasicules have?

Answer 32

Larger area | Stronger

Question 33

What is the equation for force?

Answer 33

F=(Vσ)/length

Question 34

Where are tendons in bipinnate muscles?

Answer 34

Intramuscular

Question 35

How fast is ATP hydrolysis in muscle?

Answer 35

10^9 faster than normal

Question 36

How many ATP are hydrolysed per second?

Answer 36

4

Question 37

What is Mg needed for in muscle?

Answer 37

Coordination of 4 Water and Phosphates of ATP

Question 38

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

Answer 38

P loop locks ATP in the active site | S/T residues coordinate H2O

Question 39

How does ATP hydrolysis prime myosin to bind to actin?

Answer 39

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

Question 40

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

Answer 40

Actin-Myosin

Question 41

What drives the powerstroke?

Answer 41

Release of phosphate

Question 42

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

Answer 42

12nm

Question 43

How does ATP binding act in the cross bridge cycle?

Answer 43

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

Question 44

When does ATP hydrolysis occur in the cross bridge cycle?

Answer 44

When detached

Question 45

What form is most myosin in the cross bridge cycle?

Answer 45

ATP/ADP+Pi bound | Detached from actin

Question 46

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

Answer 46

Straight relay helix of A.M

Question 47

How many actin subunits bind per myosin head?

Answer 47

5

Question 48

What residues control the relay helix kink?

Answer 48

Hydrophobic

Question 49

How much energy does ATP hydrolysis provide?

Answer 49

-60kJ/mol

Question 50

How much force does 1 Joule provide?

Answer 50

1N/m

Question 51

How efficient is myosin ATPase?

Answer 51

60%