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

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