Because the H-zone and I-bands reduce in size when contracting.
4 of 38
What does not change length during contraction?
The A-bands
5 of 38
Name the 2 types of protein filaments involved in muscle contraction
Thin actin and thick myosin
6 of 38
Describe the appearance of the actin filaments.
2 strands which are coiled around each other.
7 of 38
What is each actin strand composed of?
G actin subunits.
8 of 38
Which molecules coil around the F actin and why?
Tropomyosin molecules, to reinforce the actin.
9 of 38
What is a troponin complex attached to and what is it made up of?
Attached to tropomyosin and made up of 3 polypeptides.
10 of 38
Where do these polypeptides bind to?
1 binds to actin, 1 to tropomyosin and 1 to calcium ions.
11 of 38
What are thick filaments?
Bundles of the protein myosin.
12 of 38
What does each myosin molecule consist of?
A tail and 2 protruding heads.
13 of 38
What does each thick filament consist of?
Many myosin molecules whose heads stick out from opposite ends of the filament.
14 of 38
1st stage of muscle contraction
An action potential arrives at a neuromuscular junction
15 of 38
2nd stage
Ca2+ ions are released from the sarcoplasmic reticulum.
16 of 38
3rd stage
Calcium ions bind to troponin molecules, changing its shape.
17 of 38
4th stage
Pushes tropomysoin out of the way, exposing myosin binding site to the actin.
18 of 38
5th stage
Myosin heads bind to the binding sites and form cross-bridges.
19 of 38
6th stage
Head group of myosin heads bends, pushing actin filament along, increasing overlap of actin and myosin fibres.
20 of 38
7th stage
ADP and Pi are released.
21 of 38
8th stage
ATP attaches and cross-bridges are broken.
22 of 38
9th stage
ATP is hydrolysed (ADP and Pi remain attached to myosin heads).
23 of 38
10th stage
Myosin head is 'cocked' back.
24 of 38
What happens as cross-bridges are made and broken?
Actin filaments slide past the thick myosin filaments and shorten the sarcomere.
25 of 38
What do tropomyosin subunits cover?
The binding sites for myosin head group on actin fibre.
26 of 38
What does this coverage mean?
Cross-bridges cannot form, a myosin head group cannot attach to a binding site, muscle contraction cannot occur.
27 of 38
Where are calcium ions released from?
Sarcoplamic reticulum in sarcomeres.
28 of 38
What do calcium ions diffuse through and bind to?
Diffuse through sarcoplasm and bind to troponin molecules.
29 of 38
What does this binding lead to?
Changing shape of troponin molecules, which moves tropomyosin away from binding sites on the actin.
30 of 38
What can happen when the actin and myosin binding sites are uncovered?
Cross-bridges can form.
31 of 38
What happens when nervous stimulation stops?
Calcium ions are actively transported into the sarcoplasmic reticulum by carrier proteins on the membrane.
32 of 38
What do these actions lead to?
Muscle relaxation.
33 of 38
When are the molecules most stable during muscle contraction?
When the myosin head group attaches to the actin binding site and bends.
34 of 38
What is ATP energy required for?
To break the cross-bridge connection and re-set the myosin head forwards.
35 of 38
What does this then allow the myosin head group to do?
Attach to the next binding site along the actin molecule and bend again.
36 of 38
Why must ATP be regenerated?
To allow continued contraction.
37 of 38
Name the 3 mechanisms to maintain the supply of ATP
Aerobic respiration in muscle cell mitochondria, anaerobic respiration in muscle cell sarcoplasm and transfer from creatine phosphate in the muscle cell sarcoplasm.
Comments
No comments have yet been made