Muscle Contraction

Question 1

What does tropomyosin cover when muscles are relaxed?

Answer 1

binding sites on actin

Question 2

Where are Ca2+ ions released from?

Answer 2

sarcoplasmic reticulum

Question 3

What do the Ca2+ ions cause?

Answer 3

causes tropomyosin to move and expose the binding sites on actin (by binding to troponin)

Question 4

What can happen when the binding sites are exposed?

Answer 4

myosin heads can bind to the binding sites on actin, forming a crossbridge

Question 5

What happens after a crossbridge is formed?

Answer 5

tension occurs as a result of the angle, which leads to the actin being pulled and sliding along the myosin

Question 6

What can happen when the binding sites are exposed?

Answer 6

myosin heads can bind to the binding sites on actin, forming a crossbridge

Question 7

What does the sliding movement of actin result in?

Answer 7

the release of ADP and Pi

Question 8

What happens when a new ATP molecule binds to the myosin head?

Answer 8

the myosin head changes shape slightly, meaning the binding site is no longer complementary so myosin detaches from the actin

Question 9

What enzyme is found in the sarcoplasm?

Answer 9

ATPase

Question 10

What does the ATPase do in the context of muscle contraction?

Answer 10

hydrolyses the ATP on the myosin head causing the shape to return to normal, therefore it is once again complementary to actin

Question 11

What activates ATPase?

Answer 11

Ca2+ ions

Question 12

What is the role of phosphocreatine?

Answer 12

provides phosphates to help regenerate ATP from ADP

Question 13

What happens to the length of the sarcomere when the muscle contracts?

Answer 13

sarcomere shortens

Question 14

What happens to the H-zone and I band as the muscle contracts?

Answer 14

it shortens

Question 15

What happens to the length of the A-band as the muscle contracts?

Answer 15

stays constant

Question 16

How does a muscle contract?

Answer 16

• 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

Question 17

What is the role of ATP in muscle contraction?

Answer 17

• 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

Question 18

What is the role of Ca2+ in muscle contraction?

Answer 18

• binds to tropomyosin causing a conformational change which exposes actin-myosin binding sites
• activates ATPase

Question 19

Explain how a decrease in Ca2+ in muscle tissues could decrease the force of muscle contraction…

Answer 19

• 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

Question 20

Why can trained muscle exercise for longer than untrained?

Answer 20

• more aerobic respiration
• more ATP produced
• delayed/less anaerobic respiration
• less lactate

Question 21

Why does a fall in pH prevent Ca2+ ions stimulating muscle contraction?

Answer 21

• change in shape of Ca2+ receptors
• fewer Ca2+ ions bind to receptors
• fewer tropomyosin molecules move
• fewer binding sites exposed
• fewer myosin molecules bind

Question 22

Why is ATP a suitable energy source for cells?

Answer 22

• little energy lost as heat
• releases energy instantaneously