E-C Coupling and Cross Bridge Linking

Question 1

Why are Myofibrils multinucleate?

Answer 1

As they form from the fusion of myoblasts during development

Question 2

What protein is found in thick filaments?

Answer 2

Myosin

Question 3

What proteins are found in thin filaments?

Answer 3

Actin, tropomyosin and troponin.

Question 4

Are A bands light or dark bands?

Answer 4

Dark bands

Question 5

Are I bands light or dark bands?

Answer 5

Light bands

Question 6

What are A bands comprised of?

Answer 6

Thick filaments with thin filaments that overlap it on either end

Question 7

What is he H zone?

Answer 7

The area on the A band that is solely thick filaments as the thin don’t reach.

Question 8

What is the M line?

Answer 8

A series of proteins that that hold units together

Question 9

What is the I band comprised of?

Answer 9

Thin filaments from the end of the A band

Question 10

Where to two Sarcomeres bind?

Answer 10

At the Z line

Question 11

How does muscle growth occur?

Answer 11

By the addition of Sarcomeres

Question 12

How many thin filaments surround each thick filament?

Answer 12

Six

Question 13

How many thick filaments surround each thin filament?

Answer 13

Three

Question 14

What gives the appearance of striation?

Answer 14

Aligned A bands

Question 15

What is the main structural component of think filament?

Answer 15

A double traded helix of f actin

Question 16

What is the structure of troponin?

Answer 16

It has 3 spherical components: troponin c, troponin I and troponin T

Question 17

What is the function of troponin T?

Answer 17

It binds a single molecule of tropomyosin

Question 18

What is the function of troponin I?

Answer 18

It binds to actin and inhibits contraction

Question 19

What is the function of troponin C?

Answer 19

It binds calcium ions.

Question 20

What is the structure of myosin?

Answer 20

It is comprised of two subunits with intertwining tails and globular heads which contain an actin binding site and an ATP-are site.

Question 21

How do the fibres of myosin run?

Answer 21

Half in one direction, half in the other

Question 22

What is each myosin II molecule comprised of?

Answer 22

A double trimmer of 2 heavy chains, 2 regulatory chains and 2 alkali chains

Question 23

What happens at the hinge of the myosin molecule?

Answer 23

It opens to form heads

Question 24

How does the regulatory chain of myosin regulate ATPase activity?

Answer 24

Via phosphorylation by kinases

Question 25

What is the energy source for cross-bridge linking?

Answer 25

Hydrolysed ATP

Question 26

What is the means of muscle contraction?

Answer 26

Sliding filament action

Question 27

Which filaments move during sliding filament action?

Answer 27

Thin filaments

Question 28

Is A band width affected by sliding filament action?

Answer 28

No

Question 29

How is I band width affected by sliding filament action?

Answer 29

It decreases

Question 30

How is H zone width affected by sliding filament action?

Answer 30

It decreases

Question 31

What happens to the distance between z lines during sliding filament action?

Answer 31

It decreases

Question 32

What is the action of all six thin filaments around a thick filament in sliding filament action?

Answer 32

They are simultaneously pulled inward

Question 33

What is rigor mortis?

Answer 33

Sarcomeres stuck in contraction as ATP cannot be produced post mortem and so they are stuck in cross bridge linking

Question 34

What determines the duration of muscle contraction?

Answer 34

The duration of time in which cytosolic Ca levels are elevated

Question 35

What are t-tubules?

Answer 35

Invaginations in the sarcolemma

Question 36

Where do t-tubules penetrate the muscle?

Answer 36

At A-I band junctions

Question 37

Of what is a triad comprised?

Answer 37

A t-tubule and 2 cisrternae

Question 38

To what does depolarisation of the t-tubule membrane lead?

Answer 38

Calcium ion release from the triad

Question 39

What is required to terminate contraction?

Answer 39

Reuptake of Ca into sarcoplasmic reticulum

Question 40

What activates troponin C and so causes cross bridge cycling?

Answer 40

Increase in intracellular Ca concentration

Question 41

How may cells get rid of excess Ca to terminate contraction?

Answer 41

By extrusion through NCX exchanger or by intake into the SR by PMCA pump

Question 42

What mediates Ca uptake?

Answer 42

SR Ca pump

Question 43

What inhibits the Sr Ca pump?

Answer 43

High Ca concentration in SR

Question 44

What is the principle Ca binding protein in the SR?

Answer 44

Calsequestrin

Question 45

what is Calreticulum?

Answer 45

A Ca binding protein found in high concentrations in the SR of smooth muscle

Question 46

How many Ca can each protein in the SR bind?

Answer 46

Up to 50

Question 47

What is the function of the SERCA pump?

Answer 47

Restores Ca concentration to resting concentration

Question 48

When does contraction occur?

Answer 48

During the excitatory pulse of calcium

Question 49

What must occur for a contraction to continue?

Answer 49

A series of action potentials followed by a series of Ca excitatory pulses

Question 50

What is the sliding action?

Answer 50

The time required to bring about tensions for contraction

Question 51

What is the latent period?

Answer 51

The time delay between stimulation and contraction

Question 52

What is the contraction time?

Answer 52

The time from contraction onset to peak tension

Question 53

When does the contractile response end?

Answer 53

When the lateral sacs have taken up all the Ca released by the action potential

Question 54

What is the relaxation time?

Answer 54

The time from peak tension to full relaxation

Question 55

When does the EPP and the AP stop?

Answer 55

When AChE removes ACh from the NMJ

Question 56

What triggers Ca pumps to return Ca into the SR?

Answer 56

The local AP no longer being in the t-tubules

Question 57

What triggers the troponin-tropomyosin complex to return to its blocking position that block a cross-bridge link?

Answer 57

Removal of cytoplasmic Ca into the SR

Question 58

What is the final step in relaxation?

Answer 58

Thin filaments returning to their resting position

Question 59

What is RYR?

Answer 59

A Ca channel on the membrane of the SR

Question 60

What changes the conformation of RYR and opens it?

Answer 60

Physical attachment of DHP in response to the AP

Question 61

What happens to allow myosin binding sites on actin to become free?

Answer 61

A conformational change in tropomyosin

Question 62

What ill happen if Ca is still present father a power stroke has occurred?

Answer 62

Another power stroke will arise

Question 63

What allows myosin to detach from actin?

Answer 63

ATP binding