Three geneticists won the Nobel Prize for medicine this week for their studies of something that's been called cellular suicide.

How the body's cells die — or don't die when expected — may help researchers understand why some viruses and bacteria cause untimely death from such things as AIDS, stroke, heart attack and cancer.

The Nobel committee Monday awarded Sydney Brenner and John E. Sulston of Great Britain and H. Robert Horvitz of the United States for discoveries concerning how genes regulate organ development and a process of programmed cell death.

Here is a look at the exploration of new medical frontiers, as seen through the Nobel Prize committee:

2001: Leland H. Hartwell, United States; R. Timothy (Tim) Hunt and Sir Paul M. Nurse, Britain; for discovering key regulators of the process that lets cells divide, which is expected to lead to new cancer treatments.

2000: Arvid Carlsson, Sweden; Paul Greengard and Eric R. Kandel, United States; for research on how brain cells transmit signals to each other, thus increasing understanding of how the brain functions and how neurological and psychiatric disorders may be better treated.

1999: Guenter Blobel, United States, for protein research that shed new light on diseases, including cystic fibrosis and early development of kidney stones.

1998: Robert F. Furchgott, Louis J. Ignarro and Ferid Murad of the United States, for discovery of properties of nitric oxide, a common air pollutant, but also a lifesaver because of its capacity to dilate blood vessels.

1997: Stanley B. Prusiner, United States, for discovery of prions, an infectious agent at the heart of several forms of brain-wasting disease.

1996: Peter C. Doherty, Australia, and Rolf M. Zinkernagel, Switzerland, discovery of how the immune system recognizes infection.

1995: Edward B. Lewis and Eric F. Wieschaus, United States; and Christiane Nuesslein-Volhard, Germany; discoveries related to how genes control human development in the womb.

1994: Alfred G. Gilman and Martin Rodbell, United States, discovery of G-proteins and how cells confuse messages and foster diseases.

1993: Richard J. Roberts, Britain, and Phillip A. Sharp, United States, discovery of “split genes” that changed how scientists look at evolution and advanced research on hereditary diseases.

1992: Edwin G. Krebs, United States, Edmond H. Fischer, United States and Switzerland, discoveries concerning the process of “reversible protein phosphorylation” that help explain how imbalances in cells cause diseases.

1991: Erwin Neher and Bert Sakmann, Germany, discoveries concerning single ion channels in cells that shed light on

several diseases, including diabetes and cystic fibrosis.

1990: Joseph E. Murray and E. Donnall Thomas, United States, discoveries about organ and cell transplantation in treatment of human disease.

1989: J. Michael Bishop and Harold E. Varmus, United States, discovery of a family of genes that helped scientists understand how cancer develops.

1988: Sir James W. Black, Britain, research that led to a beta-blocker drug for heart disease and a

drug for peptic ulcers; and Gertrude B. Elion and George H. Hitchings, United States, research leading to drugs for AIDS, herpes, leukemia and malaria.

1987: Susumu Tonegawa, Japan, for discovering how the body is able to produce thousands of different antibodies to fight disease.

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