Bloch, Konrad Emil (1912-2000), a German-born American biochemist, shared the 1964 Nobel Prize in physiology or medicine with German biochemist Feodor Lynen for discovering how animal cells transform acetic acid into cholesterol. Bloch's findings increased the understanding of the biochemistry of living organisms and paved the way for the control of certain circulatory diseases.

Bloch was born in Neisse, Germany, now the city of Nysa, Poland. After earning the equivalent of a bachelor of science degree in chemical engineering from the technical university in Munich in 1934, Bloch left Germany, where the Nazis had come to power the previous year. Until 1936, he worked at the Swiss Research Institute in Davos, Switzerland, where he undertook experiments involving the biochemistry of phospholipids in the bacteria that cause tuberculosis.

Supported by a fellowship, he attended graduate school at Columbia University's College of Physicians and Surgeons. After earning a doctorate in biochemistry in 1938, he joined the Columbia faculty. He was invited to join the research group of Rudolf Schoenheimer, where he began working on the biosynthesis of cholesterol. Schoenheimer and his colleague, David Rittenberg, had developed a method of using radioactive isotope tracers to plot the path of certain molecules in cells. The method was helpful for studying the biochemistry of cholesterol, a wax-like substance found in all animal tissues. Before Bloch began studying cholesterol, little was known about its effects.

Bloch and Rittenberg continued to study cholesterol after Schoenheimer's death in 1941. Their research demonstrated that cholesterol is largely composed of acetate, a salt or ester of acetic acid. In 1942 and 1945, Bloch helped demonstrate the importance of cholesterol to the functioning of animal cells. It is the parent substance for the sex hormones and also supplies the bile acids that aid in fat absorption.

In 1946, Bloch left Columbia for the University of Chicago, where he rose through the ranks in the biochemistry department. In 1953, he spent a year as a Guggenheim Fellow at the Institute of Organic Chemistry in Zurich, Switzerland. When he returned to the United States, he joined the chemistry department at Harvard University, where he was Higgins Professor of Biochemistry until his retirement in 1982. From 1979 until 1984, Bloch was also professor of science in Harvard's School of Public Health.

With his research associates, Bloch studied the 27 carbon atoms that make up each cholesterol molecule. By establishing that acetate's two-carbon molecule was the building block of all cholesterol carbon atoms, Bloch's research eventually demonstrated the importance of acetic acid in making cholesterol.

At Chicago, Bloch studied the possible role of the hydrocarbon squalene in the biosynthesis of cholesterol. He injected radioactive acetic acid into dogfish livers, where squalene is produced in abundance. Later, Bloch successfully substituted rats' livers. With colleague Robert G. Langdon, Bloch proved that squalene is one of 36 steps in the biosynthetic conversion of acetate into cholesterol.

Working independently, Bloch and German biochemist Feodor Lynen each discovered that mevalonic acid is converted into isoprene, a type of hydrocarbon that is then converted into squalene. Squalene is converted into lanosterol, and further steps eventually produce cholesterol.

In 1964, Bloch and Lynen shared the Nobel Prize in physiology or medicine. Bloch continued research into the biosynthesis of both cholesterol and glutathione, a crystalline amino acid compound important in protein metabolism.