Muscle Contraction

Question 1

Describe how actin and myosin are arranged in resting muscle (3marks)

Answer 1

• Thick myosin filaments and thin actin filaments
• Not interlocked
• Wide I-bands
• Visible/wide H-zones

Question 2

What changes occur to a sarcomere when a muscle contracts?

Answer 2

• The I-band becomes narrower
• The Z-ines move closer together (sarcomere shortens)
• The H-zone disappears
• The A-band stays the same width

Question 3

What are the two types of muscle fibre?

Answer 3

• Slow-twitch fibres

- Fast-twitch fibres

Question 4

Describe the contraction of a skeletal muscle.

Answer 4

The sliding filament mechanism

-The process involves the actin and myosin filaments sliding past one another.

Question 5

Describe actin

Answer 5

Thinner and consists of two strands twisted around one another.

Question 6

Describe myosin

Answer 6

Thicker, long rod-shaped fibres with bulbous heads that project to the side.

Question 7

What is tropomyosin?

Answer 7

A fibrous strand around actin filaments

Question 8

What is troponin?

Answer 8

A globular protein involved in muscle contraction

Question 9

Describe muscle contract?

Answer 9

• Tropomyosin blocks the myosin binding sites on actin
• Calcium ions bind to the actin, displacing the tropomyosin and exposing the binding sites.
• Myosin head can now attach to the actin filaments (cross-bridge formation)
• Myosin head changes angle, causing a ratchet mechanism that slides actin relative to myosin
• Binding of ATP causes the myosin head to detach from the actin
• Hydrolysis of ATP releases energy, which allows the myosin head to resume its normal position.