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DNA Structure

Module by: Diego Moreno. E-mail the author

Summary: Discovery of the DNA structure

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 offspring, 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 scientific journal Nature in its 171st volume on pages 737–738 (dated April 25, 1953). It was the first publication which described the discovery of the double helix structure of DNA. This discovery had a major impact on biology, particularly in the field of genetics.

Figure 1
Figure 1 (Imagen 8.png)

James Watson & Francis Crick

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.

Figure 2
Figure 2 (Imagen 9.png)

Photo of DNA Molecule by Rosalind Franklin

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 first 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Much of the data that were used by Crick and Watson came from unpublished work by Maurice Wilkins, Rosalind Franklin, A.R. Stokes, and H.R. Wilson at King's College London in the University of London.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 double-helical, molecular structure of DNA called The Double Helix, and which was not accepted—at 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 seen—without her permission—the B-DNA X-ray diffraction 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.

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 justification 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 justification 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 diffraction patterns of helical structures of atoms, correctly interpreted further one of Dr. Franklin's experimental findings 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 diffraction 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 confidential, and had been designed as part of an effort to promote contact between different 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
Figure 3 (Imagen 11.png)

Rosalind Franklin - Dark Lady of DNA

Watson and Crick contribution

Watson and Crick put forward a radically different 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 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
Figure 4 (Imagen 4.png)

Molecular Structure

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