Mechanism Of Muscle Contraction Flashcards
(6 cards)
1
Q
Describe the structure of actin filaments.
A
- thin protein filaments made up of many actin monomers
- each monomer has a binding site complementary to myosin
- tropomyosin proteins are attached to actin and cover binding sites
2
Q
Describe the structure of myosin filaments.
A
- thick protein filaments made of repeated units with 2 globular heads which can move back and forth
- each myosin head has a binding site complementary to actin
- ATP is attached to the myosin head and covers the binding site
3
Q
What is the role of calcium ions during muscle contraction?
A
- attach to tropomyosin and move it away from the binding site on actin
- activates ATP Hydrolase which hydrolyses ATP on the myosin filament into ADP + Pi, exposing the binding site on myosin head
4
Q
Describe the process of muscle contraction.
A
- Calcium ions are released from the sarcoplasmic reticulum and diffuse through the myofibrils
- Calcium ions attach to tropomyosin and moves it away from the binding site on actin
- Calcium ions activate ATP Hydrolase and hydrolyses ATP into ADP + Pi which exposes the binding site on the myosin head
- Myosin head attaches to the complementary actin binding site forming an actinomyosin cross-bridge
- The energy release from hydrolysing ATP makes each myosin head bend, pulling actin over the myosin a short distance
- Another ATP molecule attaches to the myosin head which breaks the crossbridge, so releases myosin from actin
- The myosin head can then repeat the process by attaching to another actin binding site, so sliding the actin along further
5
Q
Why is muscle contraction smooth and not jerky?
A
Not all the myosin heads bind to actin at once
6
Q
How is the muscle returned back to its relaxed state?
A
- calcium ions are reabsorbed into the sarcoplasmic reticulum by active transport
- tropomyosin moves to cover the binding sites on actin
- ATP attaches to myosin head
- this causes actin and myosin to detach
