CHAPTER
7Reflecting
Questions
Nucleic Acids: The
Molecular Basis of Life
216
The bear on the opposite page is
neither a polar bear nor an albino; it
is a Kermode bear (Ursus americanus
kermodei). About 10 percent of
Kermodes, like the individual shown
here, sport the white or cream fur
colour that has earned these animals
their popular “Spirit bear” name. The
Kermode is a subspecies of the black
bear, found only in a small portion of
coastal British Columbia and Alaska.
In contrast, the salmon on which this
bear is about to feed travelled
thousands of kilometres through the
open ocean before returning to spawn
in the same stream in which it
hatched four years earlier.
The Kermode’s colour is due to
genetic traits. Similarly, the salmon’s
ability to navigate out to sea and home
again is also due in large part to
genetic traits. The molecular structures
and processes that govern the
development of each animal are
the same — as they are in all living
organisms. But how can the same
structures and processes be responsible
for features as different as fur colour
and a homing instinct? How can these
traits be transmitted so accurately
from one generation to the next?
The photomicrograph shows a
molecule of DNA in the process of
replicating. In 1943, the atomic
physicist Erwin Schrödinger predicted
that the secret to life would be found
in a special crystal. A decade later,
Watson and Crick discovered the
structure of DNA, a crystalline
molecule capable of infinite internal
variation, yet reproducible withincells with astonishing accuracy. This
combination of rich variety and
stability allows DNA to guide an
infinite number of hereditary traits
while ensuring that each trait is
passed on generation after generation.
Over the twentieth century,
research on inheritance took
scientists from the observation of
physical characteristics into the inner
workings of the cell nucleus, and
from the first identification of nucleic
acids to an understanding of the
precise structure and arrangement of
DNA within living cells. In this
chapter you will follow the same
path of exploration as you study the
molecular structures and processes
that work together to encode and
transmit hereditary information.
The unique molecular properties
of DNA allow it to both store and
transmit hereditary information.How did the discovery
of the role of DNA change
our understanding of
cellular processes and
heredity?
How does the structure
of DNA contribute to its
function as the material
of heredity?
How do the structure
and function of genetic
material in bacteria
compare with those in
plants and animals?Prerequisite
Concepts
and Skills
Before you begin this chapter,
review the following concepts
and skills:
distinguishing between
the cell structure and
metabolic processes in
prokaryotes and
eukaryotes (Chapter 3,
section 3.2),
understanding cell life
cycle and cell division
(Appendix 4).