14.2 Myosin Motors Flashcards
() is a molecular motor - a protein that converts chemical energy (ATP) to mechanical energy → generates force and movement
myosin
what does a molecular motor do
a protein that converts chemical energy (ATP) to mechanical energy → generates force and movement
skeletal muscles are bundles of () - single large cells formed by the fusion of many individual cells during development
muscle fibers
most of the cytoplasm of muscle fibers consists of () - cylindrical bundles of thick myosin filaments and thin actin filaments
myofibrils
myofibrils are cylindrical bundles of thick (1) and thin (2)
- myosin filaments
- actin filaments
each myofibril is organized as a chain of contractile units called () → responsible for the striated appearance of skeletal and cardiac muscle
sarcomeres
ends of sarcomeres are defined by ()
Z discs
actin filaments are attached to Z discs at their ()
plus ends
myosin filaments are present in the () band of sarcomeres
dark A
on the other hand, myosin is absent in the () band of sarcomeres
light I
actin filaments overlap with myosin at their ()
minus ends
in the () of the sarcomere, ONLY myosin is present
H zone
sarcomeres are symmetrical about the (), where the myosin filaments are anchored at the center of the sarcomere
M-line
the sliding filament model states that ()
muscle contraction results from actin and myosin filaments sliding past one another
which bands in the sarcomere shorten during muscle contraction? which bands stay the same width?
- I bands and H zones become thin (almost completely disappear)
- A band stays the same width
molecular basis of actin-myosin sliding interaction is the ()
binding of myosin to actin filaments → myosin functions as a motor that drives filament sliding
the myosin type in muscle
myosin II
myosin II (myosin type in muscle) has ()
2 heavy chains and 2 pairs of light chains
each myosin protein consists of a (1) region and a (2) region
- globular head
- long ⍺-helical tail
how are cross-bridges between thick and thin filaments in muscle formed
globular heads of myosin bind to actin
activity of myosin as a molecular motor is powered by ()
binding and hydrolyzation of ATP at its head group
overview of movement cycle of actin-myosin
- myosin (no ATP) is tightly bound to actin
- ATP binding at myosin head groups dissociates actin-myosin complex
- hydrolysis of ATP induces a conformational change in myosin → affects neck region of myosin that binds light chains
- light chains on myosin act as a lever arm to displace myosin head by about 5 nm
- products of hydrolysis (ATP and Pi) remain bound to myosin head currently in a “cocked” position
- myosin head rebinds at a new postion on actin filament → results in release of Pi
- release of Pi triggers a “power stroke” in which ADP is released and myosin head returns to initial conformation → actin slides towards M line
muscle contraction is triggered by nerve impulses that stimulate the release of Ca2+ from the ()
sarcoplasmic reticulum
how does the release of Ca2+ contribute to muscle contraction
high Ca2+ concentrations cause a shift in the troponin-tropomyosin complex position, allowing myosin heads to interact with actin filaments
the troponin complex is composed of:
- troponin I - inhibitory
- troponin C - Ca2+ binding
- troponin T - tropomyosin binding
contractile assemblies (contractile rings) in nonmuscle cells function primarily in ()
cell division (cytokinesis)
actin-myosin filaments in nonmuscle cells aren’t ()
organized into sarcomeres
give 2 examples of contractile assemblies in nonmuscle cells
- stress fibers - contraction produces tension across the cell → cell is able to pull on a substratum
- adhesion belts - contraction alters the shape of epithelial cell sheets
toward the end of mitosis (in yeast and animal cells), a () consisting of actin and myosin II filaments is assembled by membrane-bound myosin beneath the plasma membrane
contractile ring
contraction of actin-myosin in nonmuscle cells is regulated primarily by the ()
phosphorylation of the regulatory light chain on myosin II
phosphorylation of regulatory light chain on myosin II is catalyzed by ()
myosin light-chain kinase
myosin light-chain kinase is regulated by the Ca2+ binding protein ()
calmodulin
how does phosphorylation contribute to contraction of contractile assemblies on nonmuscle cells
promotes assemply of myosin into filaments and increases myosin catalytic activity → enables contraction to proceed
how does calmodulin regulate MLCK?
increased cytosolic Ca2+ promotes binding of calmodulin to kinase → responsible for activating myosin in smooth muscle and nonmuscle cells by phosphorylating the regulatory light chain on myosin II
() are nonmuscle myosins that don’t form filaments and are not involved in contraction
unconventional myosins
2 examples of unconventional myosins
myosin I and myosin V
unconventional myosin involved in vesicle transport; its movement along actin can move cargo
myosin I
unconventional myosin important for vesicle/cargo transport in neurons
myosin V
