Page 160 - The Miracle of Protein

158 THE MIRACLE OF PROTEIN

Myosin family
Myosins are proteins programmed to walk on the actin fil-

aments. If we think of the microtubules as the highways of the
cell city, the actins can be compared to the byways. Although
actins are thinner and shorter compared to microtubules, they
are widely dispersed across the cell. Actin filaments also have
(+) and (-) end. The first member of the myosin family was dis-
covered in muscle cells. Thousands of myosin II proteins in the

muscular cells come together and begin to walk at the same
time in the same direction. This molecular gait enables your
muscular cells to contract and relax, in other words, enable you
to move. As you read this, your eyes move from one word to

another. During this time billions of myosin II molecules si-
multaneously move in the same direction along actin rails in in-
credibly short times.
It was discovered that myosin V molecule, which works
with kinesin and dynein motor proteins in the intracellular and
extracellular transport of organelles and vesicles (bags for car-

rying substances around) also has two legs and move by walk-
ing. Researchers revealed that in its every step by exerting ener-
gy (ATP) the myosin V covers a distance that is 4 to 5 times
longer (37 nm) than kinesin. This tiny molecule is able to heave
organelles that are 1000 times heavier than itself, and take hun-

dreds of steps. The long strides of myosin V compared to other
motor proteins, made it quite popular research topic among
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scientists. Another example can be found in the digestive sys-
tem. As you know, the digestion process starts in the mouth.
Every bite in our mouth is subjected to a very comprehensive
digestion process, with billions of smooth muscle cells in play

in a system that is out of our control. Myosins ensure the move-