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what does myosin I do?
carries substrates as a single unit ( membrane bound vesicles or plasma membrane)
what does myosin II look like?
dimer - two tails twist around each other to form a coiled-coil configuration
the myosin II heads ______
point outward on either end of the thick filament to interact with actin thin filaments
what does the sliding filament theory state
contraction is caused by a simultaneous shortening of all the sarcomeres. there is no change in the length of either kind of filament
myosin activity cycle step 1
atp binding causes detachment from the target actin filament, which allows sliding and movement to take place later
myosin activity cycle step 2
ATP hydrolysis results in the head moving to the cocked position. the angle of the head changes and binds weakly to the next actin unit
myosin activity cycle step 3
the binding of hte head to actin results in a conformational change releasing the inorganic phosphate
myosin activity cycle step 4
power stroke: release of the inorganic phosphate initiates the power stroke that forcibly returns the head to its initial uncocked position. release of ADP follows rapidly after release of inorganic phosphate as the head returns to the initial position - cycle can start over
binding of ____ to ____ results in a conformational change that shifts _____ in position, revealing the myosin-binding sites on the actin filament
ca, troponin, tropomyosin
increase in ________ triggers coordinated actin/myosin II interaction
muscle cell cytoplasmic [Ca2+]
______ ____ and ______ _____work togehter to coordinate contraction
T-tubules, sarcoplasmic reticulum
electrical information is communicated to the interior of the muscle fiber by t tubules results in ___ ____ from the ____ _____
calcium release, sarcoplasmic reticulum
steps of musicle contraction/ca
1. AP stimulates muscle
2. a muscle AP follows t tubules deep into muscle fiber
3. this stimulates the release of ca by sarcoplasmic reticulum
4. ca and atp are required for thick/thin filament contraction ( by myosin II/actin interaction)
5.when electric potential of the muscle plasma membrane returns to normal, ca is pumped back in the sarcoplasmic reticulum by a powerful ca pump proteins
how does an AP result in the release of ca into the cytoplasm?
AP causes a change in a voltage sensitive protein (DHP receptor) in the t tubule membrane. this conformational change triggers opening of ion channels (RYANODINE RECEPTORS) in the sarcoplasmic reticulum releasing ca into the cytoplasm. t tubule membrane and SR are close to each other
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