Made up of several hundred myosin protein molecules
Muscle deactivation step 1
Ca2+ levels decrease
Muscle deactivation step 2
Troponin reverts to its original confirmation
Muscle deactivation step 3
Tropomyosin reverts, covering the myosin binding sites on the actin thin filament
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)
Thin filament structures (3)
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
Sliding filament mechanism of contraction step 2
Myosin heads in the high-energy confirmation attach to a binding site on F-actin
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
Sliding filament mechanism of contraction step 4
Actin-bound myosin heads bind ATP, which releases the heads from the actin.
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
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.
Muscle contraction activation step 1
Muscle fiber Ca2+ concentrations increase as a resulf ot a nerve signal
Muscle contraction activation step 2
Troponin binds the Ca2+ and undergoes a conformational change
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.
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
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.
Thick muscle filament structure (1)
Made up of several hundred myosin protein molecules.