1.4 – Genetic Foundations
SUMMARY 1.4 Genetic Foundations
■ Genetic information is encoded in the linear sequence of four types of
deoxyribonucleotides in DNA.
■ The double-helical DNA molecule contains an internal template for its own replication and
repair.
■ DNA molecules are extraordinarily large, with molecular weights in the millions or billions.
■ Despite the enormous size of DNA, the sequence of its nucleotides is very precise, and the
maintenance of this precise sequence over very long times is the basis for genetic continuity
in organisms.
■ The linear sequence of amino acids in a protein, which is encoded in the DNA of the gene
for that protein, produces a protein’s unique three- dimensional structure—a process also
dependent on environmental conditions.
■ Individual macromolecules with specific affinity for other macromolecules self-assemble
into supramolecular complexes.
Perhaps the most remarkable property of living cells and organisms is their ability to
reproduce themselves for countless generations with nearly perfect fidelity. This continuity
of inherited traits implies constancy, over millions of years, in the structure of the molecules
that contain the genetic information. Very few historical records of civilization, even those
etched in copper or carved in stone (Fig. 1-31), have survived for a thousand years. But
there is good evidence that the genetic instructions in living organisms have remained
nearly unchanged over very much longer periods; many bacteria have nearly the same size,
shape, and internal structure as bacteria that lived almost four billion years ago. This
continuity of structure and composition is the result of continuity in the structure of the
genetic material.
FIGURE 1-31 Two ancient scripts. (a) The Prism of Sennacherib, inscribed in about 700
BCE, describes in characters of the Assyrian language some historical events during the
reign of King Sennacherib. The Prism contains about 20,000 characters, weighs about 50 kg,
and has survived almost intact for about 2,700 years. (b) The single DNA molecule of the
bacterium E. coli, leaking out of a disrupted cell, is hundreds of times longer than the cell
itself and contains all the encoded information necessary to specify the cell’s structure and
functions. The bacterial DNA contains about 4.6 million
−10
characters (nucleotides), weighs less than 10 g, and has undergone only relatively minor
changes during the past several million years. (The yellow spots and dark specks in this
colorized electron micrograph are artifacts of the preparation.) [Sources: (a) Erich
Lessing/Art Resource, New York. (b) Dr. Gopal Murti–CNRI/Phototake New York.]
SUMMARY 1.4 Genetic Foundations
■ Genetic information is encoded in the linear sequence of four types of
deoxyribonucleotides in DNA.
■ The double-helical DNA molecule contains an internal template for its own replication and
repair.
■ DNA molecules are extraordinarily large, with molecular weights in the millions or billions.
■ Despite the enormous size of DNA, the sequence of its nucleotides is very precise, and the
maintenance of this precise sequence over very long times is the basis for genetic continuity
in organisms.
■ The linear sequence of amino acids in a protein, which is encoded in the DNA of the gene
for that protein, produces a protein’s unique three- dimensional structure—a process also
dependent on environmental conditions.
■ Individual macromolecules with specific affinity for other macromolecules self-assemble
into supramolecular complexes.
Perhaps the most remarkable property of living cells and organisms is their ability to
reproduce themselves for countless generations with nearly perfect fidelity. This continuity
of inherited traits implies constancy, over millions of years, in the structure of the molecules
that contain the genetic information. Very few historical records of civilization, even those
etched in copper or carved in stone (Fig. 1-31), have survived for a thousand years. But
there is good evidence that the genetic instructions in living organisms have remained
nearly unchanged over very much longer periods; many bacteria have nearly the same size,
shape, and internal structure as bacteria that lived almost four billion years ago. This
continuity of structure and composition is the result of continuity in the structure of the
genetic material.
FIGURE 1-31 Two ancient scripts. (a) The Prism of Sennacherib, inscribed in about 700
BCE, describes in characters of the Assyrian language some historical events during the
reign of King Sennacherib. The Prism contains about 20,000 characters, weighs about 50 kg,
and has survived almost intact for about 2,700 years. (b) The single DNA molecule of the
bacterium E. coli, leaking out of a disrupted cell, is hundreds of times longer than the cell
itself and contains all the encoded information necessary to specify the cell’s structure and
functions. The bacterial DNA contains about 4.6 million
−10
characters (nucleotides), weighs less than 10 g, and has undergone only relatively minor
changes during the past several million years. (The yellow spots and dark specks in this
colorized electron micrograph are artifacts of the preparation.) [Sources: (a) Erich
Lessing/Art Resource, New York. (b) Dr. Gopal Murti–CNRI/Phototake New York.]
