15.8- Contraction of skeletal muscle
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- Created by: Megan2413
- Created on: 29-11-17 16:54
What is the sliding filament mechansim?
The idea that thick and thin muscle filaments slide over one another in order for the muscle to contract
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Give three pieces of evidence for the sliding filament mechanism
- The I band becomes narrower - The Z lines move closer together (sarcomere shortens) - The H zone becomes narrower
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What disproves the theory that filaments themselves shorten?
The A band stays the same length which is determined by the length of myosin
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What are the three main proteins involved in the sliding filament mechanism?
- Tropomyosin - Actin - Myosin
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What is tropomyosin?
A long, thin thread wound around actin filaments
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What is myosin made up of?
A fibrous protein arranged in a filament made up of 100 molecules which is the 'tail' and a globular protein formed into two bulbous structures at one end (the 'head')
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What is actin made up of?
A globular protein whose molecules are arranged into long chains that are twisted around one another to form a helical strand
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What is the structural difference between a fibrous protein and a globular protein?
There is little or no tertiary structure in a fibrous protein hence its secondary structure is resposible for its final structure whereas a globular protein has a highly specific 3-D tertiary structure
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When an action potential reaches a muscle, how does it travel deep into the fibre?
Through a system of T tubules that are extensions of the cell-surface membrane and branch throughout the sarcoplasm
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What are the T tubules in contact with?
The sarcoplasmic reticulum
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How is a low concentration of calcium ions maintained in the sarcoplasm?
Calcium ions are actively transported from the sarcoplasm into the sarcoplasmic reticulum
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What does the action potential cause to open?
Calcium ion protein channels on the sarcoplasmic reticulum
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What happens once the calcium ion protein channels are opened?
Calcium ions diffuse into the sarcoplasm down a concentration gradient
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What causes the tropomyosin molecules to move and expose the myosin binding sites they were blocking?
The calcium ions binding to the troponin on the actin filament
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What molecules allows myosin heads to bind to the myosin binding sites on the actin filament?
ADP attached to the myosin heads
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What type of bond is formed between the myosin heads and the actin filament?
Actomyosin cross-bridges
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What happens to the myosin heads once attached to the actin filament?
They change their angle which pulls the actin filament along (to the left) and release a molecule of ADP
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What attachment causes the myosin heads to detach from the actin filamen, breaking the actomyosin cross-bridges?
The attachment of an ATP molecules to the myosin heads
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What activated ATPase to hydrolyse ATP to ADP?
Calcium ions
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What is the energy from the hydrolysis of ATP used for?
The myosin heads to return to their original position
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What reattaches itself to the myosin head?
ADP
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What does this reattachment of ADP to a myosin head cause?
The myosin heads to bind further along the actin filament to repeat the cycle of contraction
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When does the muscle start to relax?
When nervous stimulation ceases calcium ions are actively trasnported into the sarcoplasmic reticulum using energy from ATP hydrolysis- reabsorption of Ca2+ ions allows tropomyosin to block myosin binding sites on the actin filament again
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Do actin filaments move towards each other or away from each other?
Towards each other
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What two things is th energy from the hydrolysis of ATP used for during muscle contraction?
- Myosin head movement - Reabsorption of calcium ions into the sarcoplasmic reticulum by active transport
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Why is it necessary to have a means of producing ATP anaerobically in an active muscle?
The demand for ATP and oxygen may be greater than the rate at which blood can supply oxygen for respiration and ATP synthesis
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What two methods can be used to produce ATP anaerobically?
- Glycolysis - Phosphocreatine
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What is phosphocreatine?
It is stored in muscles and is a reserve supply of phosphate to recombine with ADP to regenerate ATP
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When is the phosphocreatine store replensihed?
Using phosphate from ATP when the muscle is relaxed
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What is the equation of the regeneration of ATP using phosphocreatine?
ADP + phosphocreatine ---> ATP + creatine
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What enzyme is used in this process?
Creatine phosphokinase
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Other cards in this set
Card 2
Front
Give three pieces of evidence for the sliding filament mechanism
Back
- The I band becomes narrower - The Z lines move closer together (sarcomere shortens) - The H zone becomes narrower
Card 3
Front
What disproves the theory that filaments themselves shorten?
Back
Card 4
Front
What are the three main proteins involved in the sliding filament mechanism?
Back
Card 5
Front
What is tropomyosin?
Back
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