Sliding Filament Theory

Question 1

What is mysoin and actin?

Answer 1

protein filaments involved in muscle contraction

Question 2

What happens when the muscles are relaxed in the sliding filament theory?

Answer 2

• the actin-myosin binding site is blocked by tropomyosin - a protein
• this prevents an actin-myosin cross bridge being formed

Question 3

What happens when the muscles contract?

Answer 3

• calcium ions cause the tropomyosin to move out of the binding site
• this allows the actin-myosin cross bridge to be formed
• calcium ions also activate ATPase - catalyses the breakdown of ATP into ADP + Pi - releases lots of energy
• ATP is used to change the shape of the myosin head - power stroke
• continues as long as the binding site is open
• ATP detaches the myosin head
• ATP is used to return myosin head to resting/starting position - recovery stroke
• ATP is used to reabsorb calcium ions by active transport using ATP