E-C Coupling and Cross Bridge Linking Flashcards
Why are Myofibrils multinucleate?
As they form from the fusion of myoblasts during development
What protein is found in thick filaments?
Myosin
What proteins are found in thin filaments?
Actin, tropomyosin and troponin.
Are A bands light or dark bands?
Dark bands
Are I bands light or dark bands?
Light bands
What are A bands comprised of?
Thick filaments with thin filaments that overlap it on either end
What is he H zone?
The area on the A band that is solely thick filaments as the thin don’t reach.
What is the M line?
A series of proteins that that hold units together
What is the I band comprised of?
Thin filaments from the end of the A band
Where to two Sarcomeres bind?
At the Z line
How does muscle growth occur?
By the addition of Sarcomeres
How many thin filaments surround each thick filament?
Six
How many thick filaments surround each thin filament?
Three
What gives the appearance of striation?
Aligned A bands
What is the main structural component of think filament?
A double traded helix of f actin
What is the structure of troponin?
It has 3 spherical components: troponin c, troponin I and troponin T
What is the function of troponin T?
It binds a single molecule of tropomyosin
What is the function of troponin I?
It binds to actin and inhibits contraction
What is the function of troponin C?
It binds calcium ions.
What is the structure of myosin?
It is comprised of two subunits with intertwining tails and globular heads which contain an actin binding site and an ATP-are site.
How do the fibres of myosin run?
Half in one direction, half in the other
What is each myosin II molecule comprised of?
A double trimmer of 2 heavy chains, 2 regulatory chains and 2 alkali chains
What happens at the hinge of the myosin molecule?
It opens to form heads
How does the regulatory chain of myosin regulate ATPase activity?
Via phosphorylation by kinases
What is the energy source for cross-bridge linking?
Hydrolysed ATP
What is the means of muscle contraction?
Sliding filament action
Which filaments move during sliding filament action?
Thin filaments
Is A band width affected by sliding filament action?
No
How is I band width affected by sliding filament action?
It decreases
How is H zone width affected by sliding filament action?
It decreases
What happens to the distance between z lines during sliding filament action?
It decreases
What is the action of all six thin filaments around a thick filament in sliding filament action?
They are simultaneously pulled inward
What is rigor mortis?
Sarcomeres stuck in contraction as ATP cannot be produced post mortem and so they are stuck in cross bridge linking
What determines the duration of muscle contraction?
The duration of time in which cytosolic Ca levels are elevated
What are t-tubules?
Invaginations in the sarcolemma
Where do t-tubules penetrate the muscle?
At A-I band junctions
Of what is a triad comprised?
A t-tubule and 2 cisrternae
To what does depolarisation of the t-tubule membrane lead?
Calcium ion release from the triad
What is required to terminate contraction?
Reuptake of Ca into sarcoplasmic reticulum
What activates troponin C and so causes cross bridge cycling?
Increase in intracellular Ca concentration
How may cells get rid of excess Ca to terminate contraction?
By extrusion through NCX exchanger or by intake into the SR by PMCA pump
What mediates Ca uptake?
SR Ca pump
What inhibits the Sr Ca pump?
High Ca concentration in SR
What is the principle Ca binding protein in the SR?
Calsequestrin
what is Calreticulum?
A Ca binding protein found in high concentrations in the SR of smooth muscle
How many Ca can each protein in the SR bind?
Up to 50
What is the function of the SERCA pump?
Restores Ca concentration to resting concentration
When does contraction occur?
During the excitatory pulse of calcium
What must occur for a contraction to continue?
A series of action potentials followed by a series of Ca excitatory pulses
What is the sliding action?
The time required to bring about tensions for contraction
What is the latent period?
The time delay between stimulation and contraction
What is the contraction time?
The time from contraction onset to peak tension
When does the contractile response end?
When the lateral sacs have taken up all the Ca released by the action potential
What is the relaxation time?
The time from peak tension to full relaxation
When does the EPP and the AP stop?
When AChE removes ACh from the NMJ
What triggers Ca pumps to return Ca into the SR?
The local AP no longer being in the t-tubules
What triggers the troponin-tropomyosin complex to return to its blocking position that block a cross-bridge link?
Removal of cytoplasmic Ca into the SR
What is the final step in relaxation?
Thin filaments returning to their resting position
What is RYR?
A Ca channel on the membrane of the SR
What changes the conformation of RYR and opens it?
Physical attachment of DHP in response to the AP
What happens to allow myosin binding sites on actin to become free?
A conformational change in tropomyosin
What ill happen if Ca is still present father a power stroke has occurred?
Another power stroke will arise
What allows myosin to detach from actin?
ATP binding
