Self and the Beginning of Life 33“9x6” b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity3.4 The Uniformity of Biochemistry
It is puzzling that, despite the great diversity of life forms, the under-
lying chemical processes are so astoundingly similar. I myself may look
different from a cockroach that infests my kitchen sink, but we both
use the same metabolic pathways, the same ATP as energy source,
and the same DNA for inheritance. The cockroach and I both sur-
vive on the same oxygen molecules and exhale carbon dioxide. The
lettuce I eat for salad differs from me mainly in its ability to convert
electromagnetic energy from sunlight to chemical energy, a fact that I
take advantage of by ingesting it as food. True, there are microbes (the
anaerobes) that abhor oxygen and can only thrive in a reduced environ-
ment — a vestige of past life before oxygen appeared on Earth — but
these are minor variations that do not overthrow the general outline
of uniformity.
What is most amazing is the near-universality of the genetic code
for translating DNA (and RNA) language into protein language (to be
elaborated later). Though seemingly randomly chosen at first sight, the
three-letter codes are identical not only across species but also across
major branches of life, such as between plants and animals.^10
Fig. 3.9. Tripartite interdependent components of a living system: (1) an enclosed
environment consisting of cell membrane and internal compartments; (2) energy
exchange consisting of metabolism utilizing protein enzymes; (3) information transfer
from DNA to DNA (replication) and from DNA to RNA and to protein. Note that (1) is
needed for (2) and (3); (2) is needed for (1) and (3); (3) is needed for (1) and (2).