280 JAMES WATSON AND FRANCIS CRICK
likened to studying the myriad
light patterns cast by a crystal
chandelier on the ceiling and
walls of a large room, and using
them to figure out the shapes and
positions of each piece of glass in
the chandelier.
Pauling in the lead
The British research team at the
Cavendish Laboratory was eager
to beat the American researchers,
led by Linus Pauling. In 1951,
Pauling and his colleagues Robert
Corey and Herman Branson had
already achieved a breakthrough
in molecular biology when they
correctly proposed that many
biological molecules—including
hemoglobin, the oxygen-carrying
substance in blood—have a
corkscrew-like helix shape. Pauling
named this molecular model the
alpha-helix.
Pauling’s breakthrough had
narrowly beaten the Cavendish
Laboratory and it looked as though
the precise shape of DNA’s
structure was within his grasp.
Then, early in 1953, Pauling
proposed that the structure of DNA
was in the form of a triple helix.By this time, James Watson was
working at the Cavendish
Laboratory. He was only 25 years
old, but he had the enthusiasm of
youth and two degrees in zoology,
and had studied the genes and
nucleic acids of bacteriophages—
the viruses that infect bacteria.
Crick, 37 years old, was a
biophysicist with an interest in the
brain and neuroscience. He had
studied proteins, nucleic acids, and
other giant molecules in living
things. He had also observed the
Cavendish team racing to beat
Pauling to the alpha-helix idea, and
later analyzed their mistaken
suppositions and dead-end
exploratory efforts.
Both Watson and Crick also had
experience of X-ray crystallography,
albeit in different areas, and
together they soon began musing
on two questions that fascinated
them both: how does DNA as a
physical molecule encode genetic
information, and how is this
information translated into the
parts of a living system?Crucial crystal pictures
Watson and Crick knew of Pauling’s
success with the alpha-helix model
of proteins, in which the molecule
twisted along a single corkscrew
path, repeating its main structure
every 3.6 turns. They also knew
that the latest research evidence
did not seem to support Pauling’s
triple helix model for DNA. This led
them to wonder whether the elusive
model was one that was neither a
single nor a triple helix. The two
conducted hardly any experimentsThis X-ray diffraction photograph
of DNA was obtained by Rosalind
Franklin in 1953, and was the biggest
clue to cracking DNA. The helical
structure of DNA was ascertained from
the pattern of spots and bands.