Dr. Peter Dennis Mitchell, British Biochemist

 

The Nobel Prize in Chemistry 1978 was awarded to Peter Mitchell “for his contribution to the understanding of biological energy transfer through the formulation of the chemiosmotic theory“.

Peter Dennis Mitchell (29 September 1920-10 April 1992), British biochemist

Sources: Nobel Prize Foundation: MLA style: “The Nobel Prize in Chemistry 1978“. Nobelprize.org. Nobel Media AB 2014. Web. 24 Oct 2017. http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1978/; Wikipedia: By Source, Fair use, https://en.wikipedia.org/w/index.php?curid=29893461

 

The Thesis – The rates of synthesis and proportions by weight of the nucleic acid components of a Micrococcus during growth in normal and in penicillin containing media with reference to the bactericidal action of penicillin.

 

Peter Dennis Mitchell was born in Mitcham, Surrey on 29 September 1920. His parents were Christopher Gibbs Mitchell, a civil servant, and Kate Beatrice Dorothy (nee) Taplin. His uncle was Sir Godfrey Way Mitchell, chairman of George Wimpey. He was educated at Queen’s College, Taunton and Jesus College, Cambridge where he studied the Natural Sciences Tripos specializing in Biochemistry. He was appointed a research post in the Department of Biochemistry, Cambridge, in 1942, and was awarded a Ph.D. in early 1951 for work on the mode of action of penicillin.

 

In 1955 Mitchell was invited by Professor Michael Swann to set up a biochemical research unit, called the Chemical Biology Unit, in the Department of Zoology, at the University of Edinburgh, where he was appointed a Senior Lecturer in 1961 and then Reader in 1962. From 1963 to 1965, he supervised the restoration of a Regency-fronted Mansion, known as Glynn House, at Cardinham near Bodmin, Cornwall – adapting a major part of it for use as a research laboratory. He and his former research colleague, Jennifer Moyle founded a charitable company, known as Glynn Research Ltd., to promote fundamental biological research at Glynn House and they embarked on a program of research on chemiosmotic reactions and reaction systems.

 

In the 1960s, ATP was known to be the energy currency of life, but the mechanism by which ATP was created in the mitochondria was assumed to be by substrate-level phosphorylation. Mitchell’s chemiosmotic hypothesis was the basis for understanding the actual process of oxidative phosphorylation. At the time, the biochemical mechanism of ATP synthesis by oxidative phosphorylation was unknown. Mitchell realized that the movement of ions across an electrochemical potential difference could provide the energy needed to produce ATP. His hypothesis was derived from information that was well known in the 1960s. He knew that living cells had a membrane potential; interior negative to the environment. The movement of charged ions across a membrane is thus affected by the electrical forces (the attraction of positive to negative charges). Their movement is also affected by thermodynamic forces, the tendency of substances to diffuse from regions of higher concentration. He went on to show that ATP synthesis was coupled to this electrochemical gradient.

 

His hypothesis was confirmed by the discovery of ATP synthase, a membrane-bound protein that uses the potential energy of the electrochemical gradient to make ATP; and by the discovery by Andre Jagendorf that a pH difference across the thylakoid membrane in the chloroplast results in ATP synthesis. Later, Mitchell also hypothesized some of the complex details of electron transport chains. He conceived of the coupling of proton pumping to quinone-based electron bifurcation, which contributes to the proton motive force and thus, ATP synthesis. In 1978 he was awarded the Nobel Prize in Chemistry “for his contribution to the understanding of biological energy transfer through the formulation of the chemiosmotic theory.“ He was elected a Fellow of the Royal Society (FRS) in 1974. Mitchell could not have achieved all that he did, without standing on the shoulders of at least two other great researchers (among many), Dr. Friedrich Miescher and Dr. Richard Altmann.

 

Friedrich Miescher (1844-1895)

Photo credit: copied from http://www.pbs.org/wgbh/nova/photo51/images/befo-miescher.jpg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=789048

 

 

Miescher isolated various phosphate-rich chemicals, which he called nuclein (now nucleic acids), from the nuclei of white blood cells. This took place in 1869 in Felix Hoppe-Seyler’s laboratory at the University of Tubingen, Germany, paving the way for the identification of DNA as the carrier of inheritance. The significance of the discovery, first published in 1871, was not at first apparent, and it was Albrecht Kossel who made the initial inquiries into its chemical structure. Later, Friedrich Miescher raised the idea that the nucleic acids could be involved in heredity.

 

Richard Altmann (12 March 1852 – 8 December 1900) was a German pathologist and histologist from Deutsch Eylau in the Province of Prussia. Altmann studied medicine in Greifswald, Konigsberg, Marburg, and Giessen, obtaining a doctorate at the University of Giessen in 1877. He then worked as a prosector at Leipzig, and in 1887 became an anatomy professor (extraordinary). He died in Hubertusburg in 1900 from a nervous disorder. Altmann improved fixation methods, for instance, his solution of potassium dichromate and osmium tetroxide. Using that along with a new staining technique of applying acid-fuchsin contrasted by picric acid amid delicate heating, he observed filaments in the nearly all cell types, developed from granules. He named the granules “bioblasts“, and explained them as the elementary living units, having metabolic and genetic autonomy, in his 1890 book “Die Elementarorganismen“ (“The Elementary Organism“). His explanation drew much skepticism and harsh criticism. Altmann’s granules are now believed to be mitochondria. He is credited with coining the term “nucleic acid“, replacing Friedrich Miescher’s term “nuclein“ when it was demonstrated that nuclein was acidic.

 

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