sliding filament theory and sarcomere contraction

Question 1

in a relaxed muscle

Answer 1

• the actin-myosin binding site is blocked by tropomyosin

- so actinomyosin bridge can’t form

Question 2

in a contracting muscle (what happens to get to this point)

Answer 2

an action potential has to be triggered after the neuromuscular junction and spread through the sarcolema

Question 3

in a contracting muscle…

Answer 3

• Ca2+ cause tropomyosin to move out of and expose the binding site
• so actinomyosin bridge can form
• Ca2+ also activates ATPase to hydrolyse ATP–> ADP + Pi which causes myosin heads to bend

Question 4

ATP is used to

Answer 4

• change shape of myosin head (power stroke continues as long as binding site open)
• detach myosin head by binding to it
• return myosin head to starting position
• reabsorb Ca2+ by active transport when action potential stops

Question 5

when a sarcomere contracts:

Answer 5

whole sarcomere: shortens
I band : shortens
H zone : Shortens
A band : sAme

Question 6

reasons ATP is a good source of energy for cells

Answer 6

• energy is released in small amounts
• energy released instantly
• can be rapidly resynthesised