muscles Flashcards
how is F-actin (filamentous) assembled?
actin subunits head to tail assemble to form tight righthanded helix
what is myosin II composed of?
two heavy chains and four light chains (dimerization when two alpha helices wrap around each other)
how does myosin walk towards tail of actin?
with energy from binding and hydrolyzing ATP (head)
how does actin tail interactions work in skeletal muscle?
form large bipolar thick filaments with lots of myosin heads orientated in opposite directions
how does skeletel muscle cells (fibers) formed?
fusion of many muscle cell precursors
what are sarcomeres formed from?
miniature array of parallel and partly overlapping thin and thick filaments
what is a myofibril?
cylindrical stucture that is often as long as the muscle cell
made of repeated chain of tiny sacromeres
what is the sliding filament theory?
muscle fiber contracts when myosin filaments pulla ctin filaments closer together to shorten sacromeres within fiber
how are myosin and actin filaments packed together?
with crystalline regularity
what is sacromere shortening caused by?
myosin filaments sliding past actin thin filaments (no change in length of either)
where are filaments anchored in sarcomeres?
thin filaments (actin) anchored + ends to Z disc
thick filaments anchored to M line
what does alpha-actinin do?
holds actin thin filaments together in regularly shaped bundle
what is the Z disc built from?
CapZ
what is titin?
acts as molecular sping
has long serires of immunoglobulin domains that unfold as stress is applied
keeps thick filaments poised in middle of sarcomere
what does nebulin do?
maintains length and stability of thin filaments
what initiates muscle contraction?
sudden rise in cytosolic Ca2+ concentration
what does the signal from the nerve trigger (muscle contraction)?
action potential in plasma membrane which spreads to T tubules and extend around each myofibril
what happens when incoming action potential to T tubule?
activates Ca2+ channel in membrane, opens Ca2+ release channel in sarcoplasmic reticulum membrane
what does Ca2+ flooding in cytosol iniate?
contraction of myofibrils through the troponin complex and tropomyosin
what is tropomyosin?
elongated protein that binds along groove of actin filament helix
what is troponin?
a complex of three polypeptides
what happens in resting muscle?
troponin pulls tropomyosin into position on actin filament interfering with myosin heads
what is stretch activation?
intrinsic length sensing mechanism that allows muscles to function with autonomous regulation (no Ca)
