Exam Questions

Question 1

Role of Calcium in contraction

Answer 1

• When impulse arrives at neuromuscular junction, Ca released from sarcoplasmic reticulum
• Ca diffuses through the sarcoplasm
• Ca binds to Troponin molecules
• This causes troponin to move, so tropomyosin moves and exposes myosin binding sites
• Myosin forms cross bridges with actin, allowing the contraction

Question 2

Muscle contraction after Calcium binds

Answer 2

• Troponon moves, which moves the tropomyosin
• Movement of tropomyosin exposes myosin binding sites
• Myosin forms cross bridges with actin
• ADP and Pi released from myosin head, causing it to change shape and nod forward
• This slides actin along the myosin
• ATP binds to myosin head, causing it to detach from actin
• ATPase hydrolyses the ATP to ADP and Pi
• This causes a change in shape and return to position

Question 3

Explain increasing force with more calcium concentration

Answer 3

• No increase at small values as there must be a threshold to contract
• Increase due to more Ca binding to troponin, more tropomyosin movement, more binding sites exposed, more myosin filaments interact
• So stronger contraction
• No increase after a certain value
• As all binding sites used