Lecture 7 Actin-Myosin Interaction and Force Production Flashcards
motor definition
a device which uses a form of energy to perform useful work
why is myosin a chemical motor?
converts chemical energy (~P of ATP) into work of shortening plus heat
Andrew Huxley (1954)
Interference microscopy: muscle shortening
-described shortening as a change in the stripe pattern
Hugh Huxley (1954)
electron microscopy (EM): hexagonal arrangement of thin and thick filaments
Hugh Huxley (1958) projections from the myosin filament
-13 nm long, occurred every 14.3 nm
- (1980s) add ATP to solution of actin and myosin which leads to the binding of myosin to actin
(ATP is required for cross bridge to form for myosin to bind to actin)
Contraction coupling cycle
- rest
- excitation coupling
- active contraction
- recharging system
5 subsequent response dependent on presence of Ca++
Lymn and Taylor 1971; Geeves 1991
Cycle
power stroke: reaction 6
kinetics of cycle
power stroke
reaction 6 where Pi is kicked off
kinetics of cycle
50 ms/cycle, of which 2ms is actual A*M interaction
- stroke length about 10-11nm
- each myosin head can generate about 3-4pN (3-4 X 10^-12 N)
50ms/cycle of which ____ms is actual A*M interaction
2ms
stroke length about _____
10-11 nm
each myosin head can generate about ___pN
3-4 pN
How many myosin heads have to be attached simultaneously to generate 1 kg of force?
?
restoring precontraction state
- Ca++/K+ ATPase pumps calcium back into SR
- Binds to Calsequestrin inside of SR
- pump is slow (20 ions/sec) so there are a lot of them in the SR
- Na+/K+ ATPase pump
- AChesterase breaks down ACh to Cholin and acetate
- ACh is resynthesized from choline uptake and acetate from glycolysis
- Na+/K+ ATPase pump
- plasma membrane (plasmalemma) Ca++ ATPase
AChesterase is located where
in or near the NMJ
Muscle cytosolic Calcium (what happens to restore back to resting state)
Ca++/K+ pump (electrogenic) pumps Ca++ back into the SR
- binds to calsequestrin in the SR
- pump is slow (20 ions/sec) so there are a lot of them in the SR
ACh at synapse
acetylcholinesterase breaks down ACh to choline and acetate
-located ony near, under the neuromuscular junction
resynthesis of ACh within motorneuron bouton
ACh resynthesized from choline uptake and acetate from glycolysis
neuron intracellular Na+ and K+
Na+/K+ ATPase pump
neuron intracellular Ca++
plasmamembrane Ca++ ATPase
