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Peter Dennis Mitchell

Nobel Prize in Chemistry 1978 for his contribution to the understanding of biological energy transfer through the formulation of the chemiosmotic theory.

Department of Biochemistry Part I student (1939-1941), Part II student (1941-1942), PhD student (1942-1950, PhD awarded 1951) and Demonstrator (1950-1955).

Born in Mitcham, Surrey, Peter Dennis Mitchell came up to Cambridge in 1939 to read Natural Sciences and, after taking Part II Biochemistry, completed a PhD in 1951 on the mode of action of penicillin. He held the post of Demonstrator at the Department of Biochemistry from 1950 to 1955 when he moved to Edinburgh University to set up the Chemical Biology Unit in the Department of Zoology. Illness led to his resignation in 1963 after which he supervised the restoration of Glynn House near Bodmin, Cornwall, in part as a research laboratory.

By the 1960s it had been established that ATP was the universal 'energy currency' of living cells, but the mechanism by which electron transfer is coupled to ATP synthesis in oxidative phosphorylation and in photophosphorylation remained unknown. In 1961 Mitchell proposed a completely novel explanation based on an indirect interaction between oxidizing and phosphorylating enzymes. He suggested that the flow of electrons through the enzymes of the respiratory or photosynthetic electron-transfer chains drives positively charged hydrogen ions (protons) across the membranes of mitochondria, chloroplasts and bacterial cells, generating a trans-membrane electrochemical proton gradient. The gradient consists of two components: a difference in hydrogen ion concentration (ΔpH) and a difference in electrical potential (ΔΨ). The two together form what Mitchell called the protonmotive force. The synthesis of ATP is driven by a reverse flow of protons down the gradient.

Initially received with much scepticism, Mitchell's revolutionary and Nobel Prize-winning chemiosmotic theory has shaped our understanding of the mechanisms of biological energy conservation.

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Peter Dennis Mitchell.

Credit: The Nobel Foundation.