Portrait of Sir Frederick Hopkins (1861-1947), English biochemist and Nobel Laureate. After persuing a variety of activities in early life, Hopkins eventually settled on medicine, obtaining his doctorate in 1894. In 1900 he discovered tryptophan, and that some amino acids could not be manufactured by the body but had to be ingested. These were the essential amino acids. In 1906 he first postulated the concept of trace elements in protein deficiency, later forming his theory of the 'vitamin concept'. For this he was awarded the 1929 Nobel Prize for Medicine, shared with Eijkmann. Hopkins was knighted in 1925, and was the president of the Royal Society from 1930-5.