Muscle Contraction Flashcards
What does tropomyosin cover when muscles are relaxed?
binding sites on actin
Where are Ca2+ ions released from?
sarcoplasmic reticulum
What do the Ca2+ ions cause?
causes tropomyosin to move and expose the binding sites on actin (by binding to troponin)
What can happen when the binding sites are exposed?
myosin heads can bind to the binding sites on actin, forming a crossbridge
What happens after a crossbridge is formed?
tension occurs as a result of the angle, which leads to the actin being pulled and sliding along the myosin
What can happen when the binding sites are exposed?
myosin heads can bind to the binding sites on actin, forming a crossbridge
What does the sliding movement of actin result in?
the release of ADP and Pi
What happens when a new ATP molecule binds to the myosin head?
the myosin head changes shape slightly, meaning the binding site is no longer complementary so myosin detaches from the actin
What enzyme is found in the sarcoplasm?
ATPase
What does the ATPase do in the context of muscle contraction?
hydrolyses the ATP on the myosin head causing the shape to return to normal, therefore it is once again complementary to actin
What activates ATPase?
Ca2+ ions
What is the role of phosphocreatine?
provides phosphates to help regenerate ATP from ADP
What happens to the length of the sarcomere when the muscle contracts?
sarcomere shortens
What happens to the H-zone and I band as the muscle contracts?
it shortens
What happens to the length of the A-band as the muscle contracts?
stays constant
How does a muscle contract?
- Ca2+ diffuse in to myofibrils
- cause movement of tropomyosin
- exposing binding sites on actin
- myosin head binds to binding site on actin
- hydrolysis of ATP on myosin heads causes them to bend
- pulling actin molecules
- as a new ATP attaches, myosin will detach
What is the role of ATP in muscle contraction?
- provides energy for the myosin heads to change angle
- hydrolysed to release energy which allows myosin heads to return to original position
- provides energy for the active transport of Ca2+ ions into the sarcoplasmic reticulum
What is the role of Ca2+ in muscle contraction?
- binds to tropomyosin causing a conformational change which exposes actin-myosin binding sites
- activates ATPase
Explain how a decrease in Ca2+ in muscle tissues could decrease the force of muscle contraction…
- less/no tropomyosin moves and exposes myosin binding sites on actin
- fewer myosin heads are able to bind to actin
- myosin does not move and pull actin
Why can trained muscle exercise for longer than untrained?
- more aerobic respiration
- more ATP produced
- delayed/less anaerobic respiration
- less lactate
Why does a fall in pH prevent Ca2+ ions stimulating muscle contraction?
- change in shape of Ca2+ receptors
- fewer Ca2+ ions bind to receptors
- fewer tropomyosin molecules move
- fewer binding sites exposed
- fewer myosin molecules bind
Why is ATP a suitable energy source for cells?
- little energy lost as heat
- releases energy instantaneously
