Photograph 51 Glossary of Terms

King’s College – King’s College is a public research university located in London and is the third oldest university in Great Britain. In 1946, John T. Randall, who had trained under the great Nobel Prize winning physicist, William Lawrence Bragg, was appointed Head of Physics at King’s College, London. The study of physics at King’s has a long and distinguished history, producing several Nobel Prize winners, including Charles Barkla, Sir Owen Richardson and Sir Edward Appleton for important work on x-rays, thermionics and atmospheric physics. During the nineteenth century, notable King’s scientists included the famous physicist James Clerk Maxwell, who undertook groundbreaking research on thermodynamics, and Charles Wheatstone, who pioneered the development of the telegraph and stereoscopy, and who was commemorated in the research laboratories that bear his name.

Signer DNA – Rudolf Signer was a Swiss biochemist based out of the University of Berne. Through his work, he had developed a way to extract high-quality DNA samples from the thymus glands of calves, which were fresh and easily accessible at the local butcher’s shop. Signer’s DNA samples were unique because they could be spun into thin, uniform filaments, leading to sharper x-ray photographs, making “Signer DNA” the purest DNA samples of the time. In 1950, Signer attended a meeting of the Faraday Society (founded in 1903 for the study of physical chemistry, now the Royal Society of Chemistry) in London and distributed samples of his DNA to those in attendance, including Maurice Wilkins. Before Rosalind Franklin’s arrival at King’s College, Raymond Gosling and Wilkins used the samples in order to provide the first clearly crystalline x-ray diffraction pictures of DNA.

X-ray Crystallography – The study of crystals and their structure by means of the diffraction of x-rays by the regularly spaced atoms of crystalline materials.

X-ray Diffraction  – The scattering of x-rays by the regularly spaced atoms of a crystal, useful in obtaining information about the structure of the crystal.

Sir John Turton Randall (1905 – 1984) – Sir John Turton Randall was a British physicist and biophysicist whose early work included the development of the cavity magnetron, which was a type of vacuum tube crucial to improving the performance of radar during World War II. As Wheatstone Professor of Physics at King’s College London, Randall was responsible for setting up the Medical Research Council Biophysics Unit that pioneered x-ray analysis of the DNA molecule under the supervision of Maurice Wilkins. The Biophysics Unit was later renamed the Randall Division of Cell and Molecular Biophysics.

Coal Molecules – Through her work at the British Coal Utilization Research Association (BCURA), Rosalind Franklin found that the pores in coal have fine constrictions at the molecular level, which increase with heating and vary according to the carbon content of the coal. These act as “molecular sieves,” successively blocking penetration of substances according to molecular size. Franklin was the first to identify and measure these micro-structures, and this fundamental work made it possible to classify coals and predict their performance to a high degree of accuracy. Her work at BCURA yielded a doctoral thesis, her PhD from Cambridge in 1945, and five scientific papers.

Linus Pauling (1901 – 1994) – Linus Pauling was an American chemist and biochemist. Considered one of the most influential chemists in history, he was one of the first scientists to study quantum chemistry and molecular biology. After graduating from Oregon State University in 1922, he was appointed a Teaching Fellow at California Institute of Technology and was a graduate student there until 1925, working under Professors Roscoe G. Dickinson and Richard C. Tolman. In 1925, he was awarded a PhD in Chemistry, with minors in Physics and Mathematics. In 1922, with Professor Dickinson, he began the experimental determination of the structures of some crystals, and also started theoretical work on the nature of the chemical bond. In 1951, Pauling, along with Robert Corey and Herman Branson, correctly proposed the alpha helix and the beta sheet as the primary structural motifs in protein secondary structure, thereby winning the “race” to find the alpha helix structure of proteins. When Lawrence Bragg’s team at the Cavendish learned of this discovery and that Pauling was working on molecular models for the structure of DNA (a proposed triple helix), Bragg allowed Watson and Crick to start work on their own DNA model. Though Pauling did not win “the race for DNA,” he won the Nobel Prize in Chemistry in 1954 and the Nobel Peace Prize in 1962, making him one of four people to win multiple Nobel Prizes and one of two people to win the Nobel Prize in multiple fields, the other being Madame Marie Curie.

Sir William Lawrence Bragg (1890 – 1971) – Sir William Lawrence Bragg was an Australian-born physicist and x-ray crystallographer. Known for discovering the Bragg Law of X-ray Diffraction, the work he did with his father on crystallography jointly earned them the Nobel Prize for Physics in 1915, making Bragg at the age of 25 the youngest-ever Nobel laureate. Together with his father he published various scientific papers on crystal structure after their joint publication of X-rays and Crystal Structure (1915), including The Crystalline State (1934), Electricity (1936), and Atomic Structure of Minerals (1937). Bragg, who had been elected Fellow of the Royal Society in 1921, was Director of the National Physical Laboratory from 1937 to 1938 and Cavendish Professor of Experimental Physics, Cambridge, from 1938 to 1953. He was PhD mentor to J.T. Randall, who went on to head the Biophysics Unit at King’s College, and who nominated Wilkins, Watson, and Crick for the 1962 Nobel Prize for Medicine or Physiology.

Deoxyribonucleic Acid/B Form – A self-replicating material, which is present in nearly all living organisms as the main constituent of chromosomes. It is the carrier of genetic information. Each molecule of DNA consists of two strands coiled around each other to form a double helix, a structure like a spiral ladder. Each rung of the ladder consists of a pair of chemical groups called bases (of which there are four types), which combine in specific pairs so that the sequence on one strand of the double helix is complementary to that on the other. It is the specific sequence of bases that constitutes the genetic information.

A-DNA/A Form – A right-handed double helix fairly similar to the more common and well-known B-DNA form, but with a shorter more compact helical structure. It appears likely that it occurs only in dehydrated samples of DNA, such as those used in crystallographic experiments.

Purines – The DNA bases adenine (pairs with thymine) and guanine (pairs with cytosine).

Pyrimidines – The DNA bases thymine (pairs with adenine) and cytosine (pairs with guanine).

Nucleic Acid – A complex organic substance present in living cells, especially DNA and RNA, whose molecules consist of many nucleotides (the basic building blocks of nucleic acids) linked in a long chain.

Protein – Any of a class of nitrogenous organic compounds, which have large molecules composed of one or more long chains of amino acids and are an essential part of all living organisms.

Laboratoire Centrale des Services Chimiques de L’Etat – The Laboratoire Centrale in Paris is the laboratory where Dr. Franklin worked for four years. While working there, she learned the x-ray crystallography method that was essential to her work.

Helix – An object having a three-dimensional shape like that of a wire wound uniformly in a single layer around a cylinder or cone, as in a corkscrew or spiral staircase. In biochemistry, it is an extended spiral chain of atoms in a protein, nucleic acid or other polymeric molecule.

Tobacco Mosaic Virus (TMV) – A virus which causes mosaic disease that attacks tobacco plants. It is often used in biochemical research. TMV was essential to Rosalind Franklin’s studies involving x-ray crystallography at Birkbeck College.

Cyclotron – A cyclotron is a machine used to accelerate charged particles to high energies. The first cyclotron was built by Earnest Orlando Lawrence and his graduate student, M. Stanley Livingston, at the University of California, Berkley, in the early 1930s.

The Double Helix: A Personal Account of the Discovery of the Structure of DNA – An autobiographical account of the discovery of the double helix structure of DNA, written by James D. Watson and published in 1968. Though it was originally slated to be published by Harvard University Press, Watson’s home university dropped the arrangement after protestations from Francis Crick and Maurice Wilkins, co-discoverers of the structure of DNA, and it was published privately. It has been criticized as being excessively sexist towards Rosalind Franklin. In 1998, the Modern Library placed The Double Helix at number 7 on its list of the 20th century’s best works of non-fiction.

Selected definitions from the Oxford English Dictionary.