Thick Filaments
Thick filaments are formed from a protein called
myosin
which has important properties of elasticity and
contractibility.
The shape of the myosin molecules has the apperance
of two "hockey sticks" or "golf
clubs" twisted together. This is illustrated
in the diagram above - indicating the two parts
of the myosin molecule referred
to in Advanced
Textbooks about Muscles
These are the myosin tail, and the myosin
heads, or "crossbridges"
.
Thin Filaments
The main component of the thin filaments is a
protein called actin.
Actin molecules join together forming chains twisted
into a helix configuration. These molecules are
very important to the contraction mechanism of
muscles because each actin molecule has a single
"myosin-binding site"
(not illustrated above).
The other two protein molecules that form the
thin filaments are called troponin
and tropomyosin.
The molecules of tropomyosin cover the myosin-binding
sites on the actin molecules when the muscle fibres are relaxed.
Myosin and actin form the
main contractile elements of muscles.
This is because it is the binding of the thick filaments to
the thin filaments - and in particular the
positions of these points of attachment - that controls the
state of contraction/relaxation of the muscle of which they
are apart.
Recall (from the previous
page) that the thick filaments
and the thin filaments together
form units called sacromeres.
The diagram of a sacromere is repeated below: |
