Biology B3 Muscle movement and cotnraction

Question 1

what is contraction of a muscle ?

Answer 1

Contract means get shorter. Muscles get shorter because the actin filaments slide in between the myosin filaments.

They get shorter because the different filaments slide over each other

Question 2

what are thin filaments composed of ?

Answer 2

thin filaments are composed of actin

Question 3

what are thick filaments composed of ?

Answer 3

thick filaments are composed of myosin

Question 4

when does the size of the different bands change ?

Answer 4

The size of the different bands change when a myofibril is contracting

Question 5

examples of when different bands change ?

Answer 5

The H band disappears. The z lines move close together as the sarcomere shortens

Question 6

what is the sliding filament theory ? ( 6 marks )

Answer 6

1. tropomyosin molecule prevents myosin head from attaching to the binding site on the actin molecule
2. Calcium ions released from the sarcoplasmic reticulum cause the tropomyosin molecule to change shape and so pull away from the binding sites of each actin molecule.
3. Myosin head now attaches to the binding site on the actin filament
4. Head of myosin changes angle , moving the actin filament along as it does so. The ADP molecule is released.
5. ATP molecules fixes to myosin head causing it to detach from the actin filament.
6. Hydrolyses of ATP to ADP by ATPase provides the energy for the myosin head to resume its normal position.