L8: muscle contraction Flashcards
T/F in a muscle contraction, thick and thin filaments shorten
false - they slide past each other, do not shorten
H band
myosin only portion of sarcomere
M line
line down middle of H band – where myosin separate into different polarities
I band
actin only portion of sarcomere
Z line
line down middle of I band – where actin filaments are anchored
A band
the whole myosin portion of sarcomere, including where it overlaps with actin
these bands of a sarcomere shorten during contraction
H band
I band
this protein anchors myosin to Z lines
titin
titin
anchors myosin filaments to z-lines
this protein lies along actin in the sarcomere and is thought to be a ruler to determine thin filament length
nebulin
nebulin
lies along actin in the sarcomere and is thought to be a ruler to determine thin filament length
a muscle fiber is encased by…
the sarcolemma
a muscle fibril is encased by…
sarcoplasmic reticulum
outline the pathway from motor neuron action potential to actin exposure in skeletal muscle
motor neuron ACh N1 receptor motor end plate sarcolemma t-tubule DHPR dihydropyridine receptor RYR1 ryanodine receptor Ca++ troponin c troponin i troponin t tropomyosin exposed actin
outline the pathway from neuromuscular synapse to exposed actin in cardiac muscle
synapse (cholinergic or adrenergic or other) sarcolemma t-tubule DHPR Ca++ RYR2 Ca++ troponin c troponin i troponin t tropomyosin exposed actin
how is calcium release in skeletal muscle different from calcium release in cardiac muscle?
skeletal - DHPR appears to directly activate the RYR1 channels to release Ca++
cardiac - DHPR releases Ca++, which activates RYR2 to release Ca++
DHCR in skeletal and cardiac muscle contraction is…
dihydropyridine receptor
in skeletal muscle - activates RYR1 Ca++ release
in cardiac muscle - releases Ca++, which binds RYR2 receptors and activates RYR2 Ca++ release
RYR1
ryanodine receptor 1
in skeletal muscle, is directly activated by DHPR protein of t-tuble and releases Ca++
RYR2
ryanodine receptor 2
in cardiac muscle, is activated by the Ca++ released by DHPR in t-tubule to release more Ca++
troponin c
binds calcium, signals troponin i to release actin, which signals troponin t to shift topomyosin and expose actin
troponin i
binds to actin to hold troponin-topomyosin complex in place
between troponin c and t
troponin t
binds tropomyosin, receives signal to shift from troponin c signal to troponin i
how is calcium resequestered into sarcoplasmic reticulum?
Ca++ ATPase pump
what protein buffers Ca++ concentrations in the SR so that more can be stored?
calsequestrin
calsequestrin
buffers Ca++ concentrations in the SR so that more can be stored
rigor state
all ATP has been hydrolyzed so M-ADP+Pi complex is stuck bound to actin
rigor mortis occurs because…
all ATP has been hydrolyzed so M-ADP+Pi complex is stuck bound to actin
a myosin molecule has _ heavy chains and _ light chains
2 heavy chains (binding and ATPase)
4 light chains (1 essential 1 regulatory for each heavy chain
the pivot in myosin during crossbridge cycling occurs at this location
between the head and essential light chian
what are the two myosin light chains
essential (closer to head)
regulatory (closer to tail)
how many g-actin subunits per f-actin repeat?
13-14 (non-integral)
in rigor, myosin heads are at a __ degree angle to actin
45 degree angle
in a transverse section, thin filaments are arranged in a __ pattern about thick filaments
hexagonal
how many thin filaments does one thick filament bind to?
6
in transverse section, thin filaments are arranged in a hexagonal pattern around thick filaments
why do actin-myosin crossbridges cycle in an asynchronous manner during muscle contraction?
provide gradual shortening
prevent slippage under tension
what is the rate limiting step in the myosin ATPase cycle that is catalyzed in the presence of actin?
ADP+Pi dissociation from myosin
M-ADP-Pi –> M + ADP + Pi
4 steps in actin-myosin cross bridge cycle
M ADP Pi (hydrolyzed)
A M ADP Pi (bound)
A M (stroked)
M ATP (released)
removing ATP halts the actin-myosin cross bridge cycle at which step?
rigor (prevents A-M release)
adding ATPγS halts the actin-myosin cross bridge cycle at which step?
release
prevents ATP hydrolysis and A-M binding
removing actin halts the actin-myosin cross bridge cycle at which step?
M-ADP-Pi (cannot bind)
at rest, the actin-myosin cross bridge cycle is in which step?
M-ADP-Pi (cannot bind)
adding AMPPNP halts the actin-myosin cross bridge cycle at which step?
A-M binding
AMPPNP can by hydrolyzed but not removed
how can you prevent actin-myosin release?
remove ATP
how can you prevent ATP hydrolysis by myosin?
ATPγS
can bind myosin but cannot be hydrolized
how can you prevent A-M binding?
ATPγS
can bind myosin but cannot be hydrolized
how can you prevent A-M power stroke?
AMPPNP
can be hydrolized but cannot be removed from myosin
how can you prevent M-ADP-Pi dissociation?
remove (or block) actin
M-ADP-Pi dissociation occurs very slowly on its own
how many troponin bind to one tropomyosin?
1
between troponin and tropomyosin, which is globular and which is filamentous
troponin = globular tropomyosin = filamentous
1 tropomyosin binds to how many actin monomers?
7
approximately how many troponin are there per actin filament period?
~2
7 g-actin per tropomyosin
13-14 g-actin per period
how many tropomyosin in a tropomyosin period?
how many actin in a tropomyosin period?
2 tropomyosin
14 actin
how does a tropomyosin period compare to an actin period?
roughly the same but slightly larger (14 vs about 13.5 g-actin monomers)
