The fourth and final category of biological molecule to be introduced
here is that of the nucleic acids, represented by DNA (deoxyribonu-
cleic acid) and RNA (ribonucleic acid). DNA and RNA are by far the
largest molecules in living organisms, containing many thousands,
even millions, of atoms and serving as the repositories for the infor-
mation required for constructing a living cell—the genetic or hered-
itary information. The DNA double helix is composed of two very
long chains of four component nucleotides—adenine (A), cytosine (C),
guanine (G), and thymine (T)—coupled with deoxyribose sugars and
phosphate (phosphorus and oxygen) groups. Each long chain is held
together by covalent bonds between the sugars and phosphates. The
two chains wind around one another in a helical form and are held to-
gether by noncovalent hydrogen bonds between nucleotides. Adenine
forms hydrogen bonds with thymine, and guanine forms hydrogen
bonds with cytosine.
The discovery of the double-helical structure of DNA and its ram-
ifications is one of the great sagas of twentieth-century science. The
field of molecular biology and the modern biotechnology industry
were among the offspring of this discovery. Also, among the ramifica-
tions, I believe, was the strengthening of confidence that the known
chemistry of atoms and molecules will be able to account for all the
phenomena of life, including even that of mind and consciousness.
So, let the tale betold...
Molecules and cells,
atoms play their varied roles.
Theater of life!