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40 terms

Lecture 18 - Actin, Myosin, and Skeletal Muscle Contraction

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skeletal muscle is_____
voluntary - signal from motor neuron is required
how many nuclei do sketal muscles have
multi
are skeletal muscles branched?
no
how many nuclei do cardic muscle have
1-2
what is a special characteristic of cardiac muscle
intercalated discs
is cardiac muscle voluntary or nonvoluntary
non
is cardiac muscle branched?
yes
where do you find smooth muscles?
intestines, arteries
how many nuclei does smooth muscle have?
1
is smooth muscle branched?
no
is smooth muscle voluntary?
no
organization of skeletal muscle?
sarcomere<myofibril<muscle fiber<muscle fascicle<skeletal muscle
myosin uses _____ as substrate
actin filaments
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
myosin II molecules combine to make up a _____
thick filament
the thick filament formed by myosin II are ______
bipolar
the myosin II heads ______
point outward on either end of the thick filament to interact with actin thin filaments
_______ are the contractile units of muslce
sarcomere
the _________ of ______ gives skeletal muscle a striated appearance
repeating pattern, sarcomeres
muscles contract by a _____ _____ _____
sliding filament mechanism
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
what happens if there is no ATP?
rigor mortis
what is rigor mortis?
a consequence of all myosin heads being linked to actin filaments
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
______ and ______ respond to calcium signaling to regulate muscle contraction
tropomyosin, troponin
______ overlaps with 7 actin monomers and covers the myosin binding sites
tropomyosin
______ is made up of 3 subunits, including ca binding
troponin
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
electrical information is communicated to the interior of the muscle fiber by t tubules results in ___ ____ from the ____ _____
calcium release, sarcoplasmic reticulum
muscle contraction is triggered by a rise in _____
ca2+
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
ca is released from ____ ____ in the ____ ____ ____
ion channels, sarcoplasmic reticulum membrane
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