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48
Lever arm
Myosin head
Muscles May Move Everything, But
How Does a Muscle Move?
Actin filament
Muscle molecules:
The myosin head with its lever
arm attaches itself to the
actin filament.The arm swings
round within milliseconds
(above:the lever arm before
its stroke,below:after the
stroke).As the lever arm is permanently
attached to the
myosin filament,the swinging
movement causes the
two filaments to slide alongside
one another and the
muscle to contract.
Nothing moves without muscles. Walking, climbing stairs, sitting
down—without leg muscles these activities would be unthinkable.
Picking up a sandwich and putting it in our mouths would
also be impossible without muscular power, as would swallowing
a bite of it.Whether it be breathing in or out, laughing or crying—
nothing functions without the aid of the innumerable cords of
muscle running through our bodies.
When a muscle moves, chemical energy is transformed into mechanical
work. The functional principle at the molecular level is as
follows: bundles made up of two sorts of interlocking protein
strands—the thick myosin and the thin actin filaments—glide
into one another to produce muscular movement.
Synchrotron radiation is an excellent tool for analyzing the exact
sequence of events in these processes. This is because its intense
X-ray light can be used to study the tightly bundled protein structures
in the muscle fibers with atomic precision. In fact,researchers
actually began successfully analyzing muscle contraction using
X-rays in the early 1970s. And things have developed in the meantime.
At present,about 650 scientists are working on the structural
analysis of biological molecules at DESY. Both the European Molecular
Biology Laboratory (EMBL) and the Max Planck Society (MPG)
have set up research outstations in Hamburg.
Thanks to X-ray analysis, we now have an exact understanding
of the mechanism that enables humans and animals to move.The
actual engine of muscular movement is the head of the myosin
molecule, which is linked to the actin. At the end of this head is a
lever arm that swings in a fraction of a second when chemical energy
is consumed. This swinging motion causes the actin and
myosin filaments to slide into one another,thereby contracting the
muscle.
The extremely brief and intense flashes of light produced by the
new X-ray laser could make it possible to create instantaneous
records of such molecular movements at a higher time resolution—i.e.
at shorter intervals—than was previously possible. As a
result,it would become possible to “film”molecular processes.