I do not understand DNA at all, so I have totally depended on Profiles in Science. But I do understand the sexist treatment of clever female intellectuals. British Rosalind Franklin (1920-58) was not the first woman to have endured indignities in the male-dominated world of science, but Franklin's case was the most unfair.
James Watson, Francis Crick, Maurice Wilkins, Rosalind Franklin.
Credit: Understanding Science (top images)
The 1953 discovery of the double helix, the twisted structure of deoxy-ribonucleic acid/DNA, was made by two molecular biologists: British Francis Crick (1916-2004) and American James Watson (1928- ). The two men recognised early in their careers that gaining a detailed knowledge of the three-dimensional configuration of the gene was the central problem in molecular biology. Without it, heredity and reproduction could not be understood.
They seized on this problem in 1951, and focused on it. This meant taking on the monumental task of immersing themselves in genetics, biochemistry, chemistry and X-ray crystallography (X-ray diffractions used to determine the atomic and molecular structure of a crystal). They took advantage of their great backgrounds in physics and X-ray crystallography (Crick) and viral and bacterial genetics (Watson). The two showed that DNA had a structure sufficiently complex to be the master molecule of life.
Watson's book: The Double Helix,1968
Other researchers made vital findings about the composition of DNA. Organic chemist Alexander Todd determined that the backbone of the DNA molecule contained repeating phosphate and deoxyribose sugar groups. Biochemist Erwin Chargaff found that while the amount of DNA, and its four types of bases, varied widely between species, A and T always appeared in ratios of one-to-one, as did G and C. New Zealand-British Maurice Wilkins (1916-2004) and British Rosalind Franklin obtained high-resolution X-ray images of DNA fibres that suggested a helical, corkscrew-like shape. American chemist Linus Pauling discovered the single-stranded alpha helix, the structure found in many proteins. Plus he pioneered the method of model building in chemistry by which Watson and Crick were to uncover the structure of DNA. They had to unify these disparate findings into a coherent theory of genetic transfer.
American Jerry Donohue, a visiting physical chemist, pointed out that the configuration for the rings of carbon, nitrogen, hydrogen and oxygen, the elements of all four bases, was incorrect in most chemistry textbooks. Acting on Donohue's advice in Feb 1953, Watson put the two bases into their correct form in cardboard models; he moved a hydrogen atom from a position where it bonded with oxygen to a neighbouring position where it bonded with nitrogen. While shifting around the cardboard cut-outs of the accurate molecules on his office table, Watson had a flash! He realised that A, when joined with T, very nearly resembled a combination of C and G, and that each pair could hold together by forming hydrogen bonds.
Watson and Crick published their findings in the British scientific weekly Nature, April 1953. They notably described the pairing of the bases on the inside of the two DNA backbones: A=T and C=G. The pairing rule immediately suggested a copying mechanism for DNA, an idea which was developed in a second article in Nature, May 1953. The sequence of the bases in DNA formed a code by which genetic information could be stored and transmitted.
Watson and Crick published their findings in the British scientific weekly Nature, April 1953. They notably described the pairing of the bases on the inside of the two DNA backbones: A=T and C=G. The pairing rule immediately suggested a copying mechanism for DNA, an idea which was developed in a second article in Nature, May 1953. The sequence of the bases in DNA formed a code by which genetic information could be stored and transmitted.
Watson and Crick's original article in Nature was rarely cited. Its true significance became apparent only later in the 1950s, when the their DNA structure was shown to provide a mechanism for controlling protein synthesis. Watson wrote of their collaboration in The Double Helix (1968).
But note Watson and Crick's use of Rosalind Franklin's crystallo-graphic evidence of DNA structure. It had been leaked to them by Franklin’s angry colleague, Maurice Wilkins, WITHOUT Franklin’s knowledge or permission. Wilkins took Franklin’s Photo 51, an image of DNA and the result of over 100 hours on an X-ray crystallography machine she had perfected, and showed it to Watson and Crick.
Her evidence demonstrated that the two sugar-phosphate backbones lay outside the molecule, confirming Watson and Crick's guess that the backbones formed a double helix. Franklin's superb work proved crucial in Watson and Crick's thesis; it was Photo 51 that enabled their breakthrough! While acknowledging their patronising attitude towards this very clever female scientist, Crick stated they used Franklin’s findings appropriately. But the men gave Franklin no formal acknowledgment, even after she died in 1958.
Franklin, X-ray diffraction and double helix model.
Credit: Pinterest
But her role was investigated in Anne Sayre’s book Rosalind Franklin and DNA (1975). Chilling reports concluded that science was a breeding ground for this kind of inappropriate behaviour, due to a strict, male-dominated hierarchy. So writing Franklin’s role back into this critical scientific breakthrough was doubly important.