This first essay is previously used in the chapter. You may choose to skip over it.
Nearly twenty years ago, biochemists found that a
separable constituent of the cell deoxyribonucleic (or DNA) appeared
to guide the cell's protein-synthesizing machinery. The internal
structure of DNA seemed to represent a set of coded instructions
which dictated the pattern of protein-synthesis. Experiments indicated
that in the presence of appropriate enzymes in each DNA molecule
could form a replica, a new DNA molecule, containing the specific
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