Sliding Filament Mechanism Of Muscle Contraction Flashcards
What arrives at the neuromuscular junction?
> An action potential arrives at the neuromuscular junction
What are released form the sarcoplasmic reticulum and what do they do?
> Calcium ions are released from the sarcoplasmic reticulum
> Calcium ions bind to troponin molecules, stimulating them to change shape
What do the calcium ions do to the troponin and tropmyosin and what does this lead to?
> This causes troponin and tropomyosin proteins to change position on the actin (thin) filaments
> So myosin binding sites are exposed on the actin molecules
> What does this lead the globular heads of the myosin molecules to do?
> What does this form between the two types of filament and what does this cause?
> The globular heads of the myosin molecules bind with these sites, forming cross-bridges between the two types of filament
> The formation of the cross-bridges causes the myosin heads to spontaneously bend (releasing ADP and inorganic phosphate), pulling the actin filaments towards the centre of the sarcomere and causing the muscle to contract a very small distance
ATP’s role?
ATP hydrolase’s role?
> ATP binds to the myosin heads producing a change in shape that causes the myosin heads to release from the actin filaments
> ATP hydrolase hydrolyses ATP into ADP and inorganic phosphate which causes the myosin heads to move back to their original positions
What do the myosin heads do now that they have moved back into their original positions?
What does this to do the actin filaments?
> The myosin heads are then able to bind to new binding sites on the actin filaments, closer to the Z disc
> The myosin heads move again, pulling the actin filaments even closer the centre of the sarcomere, causing the sarcomere to shorten once more and pulling the Z discs closer together
ATP’s second role?
> ATP binds to the myosin heads once more in order for them to detach again
Full explanation!
> An action potential arrives at the neuromuscular junction
> Calcium ions are released from the sarcoplasmic reticulum (SR)
> Calcium ions bind to troponin molecules, stimulating them to change shape
> This causes troponin and tropomyosin proteins to change position on the actin (thin) filaments
> Myosin binding sites are exposed on the actin molecules
> The globular heads of the myosin molecules bind with these sites, forming cross-bridges between the two types of filament
> The formation of the cross-bridges causes the myosin heads to spontaneously bend (releasing ADP and inorganic phosphate), pulling the actin filaments towards the centre of the sarcomere and causing the muscle to contract a very small distance
> ATP binds to the myosin heads producing a change in shape that causes the myosin heads to release from the actin filaments
> The enzyme ATP hydrolase hydrolyses ATP into ADP and inorganic phosphate which causes the myosin heads to move back to their original positions
> The myosin heads are then able to bind to new binding sites on the actin filaments, closer to the Z disc
> The myosin heads move again, pulling the actin filaments even closer the centre of the sarcomere, causing the sarcomere to shorten once more and pulling the Z discs closer together
> ATP binds to the myosin heads once more in order for them to detach again
