Sir John Walker FRS is Director Emeritus of the MRC Mitochondrial Biology Unit at the University of Cambridge, and a Nobel laureate. Despite Walker's third-class degree in chemistry at Oxford, in 1965 Edward Abraham took him on as a PhD student at the Dunn School, where he worked on antibiotic structure and biosynthesis. There he met many of the key players in the penicillin story, including Abraham himself, Howard Florey, Margaret Jennings (Lady Florey) and Norman Heatley.

For the next five years he did post-doctoral research in molecular biology in the US and France, before a chance meeting with Fred Sanger brought him to the MRC Laboratory of Molecular Biology in Cambridge. In 1994 he solved the structure of the catalytic region of ATP synthase, an enzyme vital to the biosynthesis of the energy-carrying molecule ATP, using X-ray crystallography, a discovery for which he shared the Nobel Prize in Chemistry in 1997.

The following year he was appointed director of the Dunn Nutritional Laboratory (renamed the MRC Mitochondrial Biology Unit in 2009) in Cambridge, the original endowment of which also came from Sir William Dunn. He retired in 2013 but remains active in research.