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DNA Structure
∗
Diego Moreno
This work is produced by OpenStax-CNX and licensed under the
†
Creative Commons Attribution License 3.0
Abstract
Discovery of the DNA structure
1 James Watson's and Francis Crick's DNA Structure
Drs. James Watson and Francis Crick's structural model of DNA that they submitted to Nature in 1953
that led to the elucidation of how genetic material is replicated and divided among ospring, launching all
of modern molecular biology. "Molecular Structure of Nucleic Acids: "A Structure for Deoxyribose Nucleic
Acid" was an article published by James D. Watson and Francis Crick in the scientic journal Nature in
its 171st volume on pages 737738 (dated April 25, 1953). It was the rst publication which described the
discovery of the double helix structure of DNA. This discovery had a major impact on biology, particularly
in the eld of genetics.
∗ Version
1.1: Nov 5, 2012 6:42 am -0600
† http://creativecommons.org/licenses/by/3.0/
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Figure 1
James Watson & Francis Crick
2 Rosalind Franklin's Contribution
However much credit is due to Rosalind Franklin's Crystal structure Photo 51 that determined the double
helix shape, and for which she never received due credit for. Franklin would help launch modern molecular
virology as well before dying of ovarian cancer at only 37.
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Figure 2
Photo of DNA Molecule by Rosalind Franklin
3 Controversy
Watson and Crick based their molecular model of the DNA double helix on data that had been collected by
researchers in several other laboratories.
Watson and Crick were the rst to put together all of the scattered fragments of information that were
required to produce a successful molecular model of DNA.
Much of the data that were used by Crick and Watson came from unpublished work by Maurice Wilkins,
Rosalind Franklin, A.R. Stokes, and H.R. Wilson at King's College London in the University of London.
In 1968, Watson published a highly controversial autobiographical account of the discovery of the doublehelical, molecular structure of DNA called The Double Helix, and which was not acceptedat least publicly
either by Francis Crick or by M.H.F. Wilkins.
In booklet, Watson stated among other things that he and Crick had access to some of Franklin's data
from a source that she was not aware of, and also that he had seenwithout her permissionthe B-DNA
X-ray diraction pattern obtained by Franklin and Gosling in May 1952 at King's in London.
In particular, in late 1952, Franklin had submitted a progress report to the Medical Research Council,
which was reviewed by Dr. Max Perutz, then at the Cavendish Laboratory of the University of Cambridge,
UK.
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Such MRC reports were not usually widely circulated, but Crick read a copy of Dr. Franklin's research
summary in early 1953.
Max Perutz's justication for passing this information to both Crick and Watson was that the report
contained information which Watson has previously heard in November 1951 when Dr. Franklin talked about
her unpublished results during a meeting arranged by Dr. M.H.F. Wilkins at King's College.
This justication does not hold however for Crick who was not present at this November 1951 meeting,
but who also was given access by Max Perutz to Franklin's MRC report data.
Moreover, Watson had acquired little training in X-ray crystallography, and therefore had not fully
understood what Dr. Franklin was saying about the structural symmetry of the DNA molecule.
Crick, however, knowing the Fourier transforms of Bessel functions that represent the X-ray diraction
patterns of helical structures of atoms, correctly interpreted further one of Dr. Franklin's experimental
ndings as indicating that DNA was most likely to be a double helix with the two polynucleotide chains
running in opposite directions.
Crick was thus in a unique position to make this interpretation because he had previously worked on the
X-ray diraction data for other large molecules that had similar, helical symmetry to that of DNA.
It is therefore questioned whether Crick's colleague, Dr. Max Perutz, acted unethically by allowing Crick
access to Dr. Franklin's MRC report about the crystallographic unit of the B-DNA and A-DNA structures.
Dr. Perutz claimed, however, that he believed he had not because this report was not condential, and
had been designed as part of an eort to promote contact between dierent MRC research groups.
By 1962, when Watson, Crick, and Wilkins won the Nobel Prize for physiology/medicine, Franklin had
died. The Nobel Prize only goes to living recipients, and can only be shared among three winners. Were she
alive, would she have been included in the prize?
Figure 3
Rosalind Franklin - Dark Lady of DNA
4 Watson and Crick contribution
Watson and Crick put forward a radically dierent structure for the salt of deoxyribose nucleic acid. One
remarkable thing about the DNA molecule is that it can build an exact copy of itself. A standard biology
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textbook states; the process of duplicating itself is known as replication. During replication, enzymes break
the weak hydrogen bonds the bases of the nucleotides. DNA separates into two halves, and this separation
exposes the nucleotide bases to its complementary base- Adenine to Thymine, Guanine to Cytosine. This
painting celebrates the marvel discovery of these two scientists and depicts the beauty of their discovery.
Figure 4
Molecular Structure
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