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Thick muscle filament structure
Made up of several hundred myosin protein molecules
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Muscle deactivation step 1
Ca2+ levels decrease
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Muscle deactivation step 2
Troponin reverts to its original confirmation
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Muscle deactivation step 3
Tropomyosin reverts, covering the myosin binding sites on the actin thin filament
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Muscle deactivation step 4
Myosin heads are no longer able to bind actin and the thick and thin filaments slide back to their original positions (muscle relaxes)
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Thin filament structures (3)
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Sliding filament mechanism of contraction step 1
Cleavage of ATP do ADP and Pi causes the myosin hinge to open, extending the head to a position further along the F-actin filament. High energy confirmation
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Sliding filament mechanism of contraction step 2
Myosin heads in the high-energy confirmation attach to a binding site on F-actin
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Sliding filament mechanism of contraction step 3
- Pi is released from myosin, causing the hinge to close. This is called a power stroke and causes the thick and thin filaments to slide past one another
- ADP is also released during the power stroke
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Sliding filament mechanism of contraction step 4
Actin-bound myosin heads bind ATP, which releases the heads from the actin.
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Tropomysin structure
A coiled, a-helical, fibrous protein that threads alont the F-actin fibers. It normally blocks the myosin binding sites on actin, unless shifted by troponin
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Troponin scructure
A trimeric, globular complex that binds the tropomysin strands at regular intervals. Troponin binds Ca2+, this binding stimulates a conformation change that results in troponin moving tropomysin away from the myosin binding sites on actin.
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Muscle contraction activation step 1
Muscle fiber Ca2+ concentrations increase as a resulf ot a nerve signal
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Muscle contraction activation step 2
Troponin binds the Ca2+ and undergoes a conformational change
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Muscle contraction activation step 3
The troponin conformational change induces a shift in the position of the tropomysin strand, exposing muyosin binding sites on the surface of the actin filament.
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Myosin structure (4)
- Protein containing two intertwining a-helical tails and two globular heads
- head contains a site that allows myosin to bind to the thin filament protein actin
- Protein hinges on the head allow it to extend out and rock back and forth
- Head also contains an ATP binding site
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Actin structure (3)
- Globular protein that polymerizes to form fibers (F-actin).
- Two F-actin fibers coil around each other to make the thin filament core.
- Contains binding sites for myosin on the thick filament.
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Thick muscle filament structure (1)
Made up of several hundred myosin protein molecules.
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Thin filament structures (3)
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