Konrad Emil Bloch (1912 –2000) shared the 1964 Nobel Prize for Physiology or Medicine with Feodor Lynen for their research on the metabolism of cholesterol and fatty acids. In 1942, Bloch and David Rittenberg discovered that acetic acid was a major building block in the 30 or more steps of cholesterol biosynthesis. Eventually, through the combined efforts of Bloch and several other researchers, the origin of each of the 27 carbon atoms of cholesterol was established. Bloch also helped identify several important reactions in the series of more than 30 reactions defining cholesterol biosynthesis -- including the cyclization of squalene to lanosterol. Bloch also investigated the enzymatic synthesis of the tripeptide glutathione and the precursor role of cholesterol in bile acids and steroid hormones.