Life's Operating Instruction

In April 1953, James Watson and Francis Crick shook the scientific
world with an elegant double-helical model for the
structure of deoxyribonucleic acid, or DNA. Figure 16.1
shows Watson (left) and Crick admiring their DNA model,
which they built from tin and wire. Over the past 50 years, their
model has evolved from a novel proposition to an icon of modern
biology. DNA, the substance of inheritance, is the most celebrated
molecule of our time. Mendel's heritable factors and
Morgan's genes on chromosomes arc, in fact, composed of
DNA. Chemically speaking, your genetic endowment is the
DNA contained in the 46 chromosomes you inherited from your
parents and in the mitochondria passed along by your mother.
Of all nature's molecules, nucleic acids are unique in their
ability to direct their own replication from monomers. Indeed,
the resemblance of offspring to their parents has its basis in the
precise replication ofDNA and its transmission from one generation
to the next. Hereditary information is encoded in the
chemical language of DNA and reproduced in all the cells of
your body. It is this DNA program that directs the development
ofyour biochemical, anatomical, physiological, and, to some extent,
behavioral traits. In this chapter, you will learn how biologists
deduced that DNA is the genetic material and how Watson
and Crick discovered its structure. You will also see how DNA
is replicated-the molecular basis of inheritance-and how
cells repair their DNA. Finally, you will explore how a molecule
of DNA is packed together with proteins in a chromosome

Cambpbell,Neil A..2008.BIOLOGY Eight edition. Pearson Education,