Topic 6- Contraction of muscles Flashcards
(29 cards)
What model is used to explain muscle contraction?
Sliding fillament model
The thick filaments within a myofibril are made up of myosin molecules: What type of protein are they and what kind of head do they have?
-Fibarous proteins
-Globular head
What is the function of the fibarous part of the mysoin molecule?
- anchors the molecule into the thick filament
In the thick filament, many myosin molecules lie next to each other with their globular heads all pointing 1.____ from the 2.___line
- away
2.M
What type of proteins are Actin?
Globular
How is one thin filament formed?
-Many actin molecules link together to form a chain
-Two actin chains twist together
What type of protein is Tropomyosin?
Fibourous
What is tropomyosin?
protein that is twisted around the two actin chains
What protein is attached to the actin chains at regular intervals?
Troponin
Explain what happens during muscle contration (according to SFT) using sacromeres and Z lines?
sarcomeres within myofibrils shorten as the Z discs are pulled closer together
What is the 1st step in muscle contraction?
An action potential arrives at the neuromuscular junction
What is a neuromuscular junction?
Interspace between effector and motor neurons
What is the 2nd step in muscle contraction?
Calcium ions are released from the sarcoplasmic reticulum (SR)
What is the 3rd step in muscle contraction?
This causes troponin and tropomyosin proteins to change position on the actin (thin) filaments
What is the 4th step in muscle contraction?
Myosin binding sites are exposed on the actin molecules
What is the 5th step in muscle contraction?
The globular heads of the myosin molecules bind with these sites, forming cross-bridges between the two types of filament
What is the 6the step in muscle contraction?
The formation of the cross-bridges causes the myosin heads to spontaneously bend (releasing ADP and inorganic phosphate),
-pulling the actin filaments towards the centre of the sarcomere and causing the muscle to contract a very small distance
What is the 7th step in muscle contraction
ATP binds to the myosin heads producing a change in shape that causes the myosin heads to release from the actin filaments
What is the 8th step in muscle contraction?
The enzyme ATP hydrolase hydrolyses ATP into ADP and inorganic phosphate which causes the myosin heads to move back to their original positions
What is the 9th step in muscle contraction
The myosin heads are then able to bind to new binding sites on the actin filaments, closer to the Z disc
What is the 10th step in muscle contraction
The myosin heads move again, pulling the actin filaments even closer the centre of the sarcomere, causing the sarcomere to shorten once more and pulling the Z discs closer together
What is the 11th step in muscle contraction
ATP binds to the myosin heads once more in order for them to detach again
What is the 12 th step in muscle contraction
As long as troponin and tropomyosin are not blocking the myosin-binding sites and the muscle has a supply of ATP, this process repeats until the muscle is fully contracted
Why si ATP required for muscle contraction?
-Energy is needed for the return movement of myosin heads that causes the actin filaments to slide
-The return of calcium ions back into the sarcoplasmic reticulum occurs via active transport
