The orderly and accurate division of cells is vital to the survival of all living things. This year's Nobel Prize in Medicine or Physiology goes to three biologistsLeland H. Hartwell, Paul Nurse and R. Timothy Huntwho have discovered the key steps that lead up to division in eukaryotic cells. Understanding these steps, known as the cell cycle, may point to new possibilities for treating cancer. Indeed, defective control of the cell cycle contributes to chromosomal changes seen in cancer cells. And some of the genes that regulate the cell cycle can also function as oncogenes.

The 2001 Nobels for Medicine or Physiology, which were announced yesterday, mark the 100th anniversary of the famous prizes, first outlined in Alfred Bernhard Nobel's will from 1895. The winners will accept their medals on December 10th with the laureates from other fields at the Stockholm Concert Hall in Sweden.Kristin Leutwyler

  • Leland H. Hartwell (below at left) of the Fred Hutchinson Cancer Research Center in Seattle was first in the early 1970s to identify the class of genesamong them one aptly named startthat control the cell cycle. Hartwell also devised the concept of checkpoints, or mechanisms that stop the cell cycle when a problem such as DNA damage arises.

  • Paul Nurse (below at right) of the Imperial Cancer Research Fund (ICRF) in London made similarly seminal findings in the mid-1970s and late 1980s. Nurse identified one of the primary regulators of the cell cycle, cyclin dependent kinase (CDK). He identified CDK's gene in yeast and human cells, demonstrated that CDK was highly conserved during evolution and revealed that CDK drove cells through the cell cycle by way of chemical reactions called phosphorylations. Read how Paul Nurse explained the cell cycle, his work and his chances for winning a Nobel Prize to Scientific American last year by clicking here.

  • R. Timothy Hunt (below center), also from the ICRF, further discovered the proteins that regulate CDK. He revealed that these proteins, called cyclins, form and degrade with each cell cycle and that their periodic degradation plays an important role in controlling the cycle.