Page 142 - The Miracle in the Cell

THE MIRACLE IN THE CELL
when a cell needs to ignore a certain part of the plan it's following,
much less who is in control of this plan overall. While some genes-that
is, files containing information about every characteristic and organ-
are inhibited at just the right time when necessary, it is not known how
some genes' "lock" is opened, who gives the command to suppress
genes or later, to negate the command and allow the gene to resume
into action. These questions have left scientists in the dark.
An invisible authority determines the correct time and place, and
how the genes are to go into action. In this way too, the cell begins to
make the necessary proteins to specialize accordingly. Skin cells, for
instance, are rich in a special protein called keratin, which gives the
skin special protection. Muscle cells are enveloped in a protein called
myosin, which has the special ability to affect a similar protein and
change its length. It can therefore facilitate the contraction of muscle
fibers. Brain cells, on the other hand, contain helper proteins that
transmit electricity. All other cells of specialized tissue produce unique
proteins to the tissue that determine the particular type of cell.
In this way, some cells produce keratin in order to become skin
cells and others, myosin to become muscle cells. Actually, all cells con-

Figure 7.9 Rod and cone cells found in the eye, which convert the image
formed on the retina into electrical signals passed along to the brain

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