Cell Division Genes and Cancer Research

The 2001 Nobel Prize in Medicine was awarded to Leland H. Hartwell, R. Timothy Hunt and Paul M. Nurse for their discoveries of key regulators of the cell cycle. Their researches are important in understanding how chromosomal abnormalities develop in cancer cells, and provide new insight into cancer treatment.


They have identified key molecules that regulate the cell cycle in all eukaryotic organisms, including yeasts, plants, animals and humans. Leland Hartwell is awarded for his discoveries of a specific class of genes that control the cell cycle. He has discovered over 100 genes involved in cell cycle control, including the gene that controls the first step in the process. Dr. Hartwell has also noticed the existence of cell cycle checkpoints, which are ordered collections of genes and proteins for preserving the integrity of cell cycle events. In the presence of damaged DNA, the checkpoints stop cell division until the damage is repaired, preventing the altered DNA from causing cell death or abnormal function in subsequent cell cycles.

Paul Nurse identified, cloned and characterized one of the key regulators of the cell cycle, CDK (cyclin dependent kinase), which drives the cell through the cell cycle by chemically modifying other proteins. He showed that the function of CDK was highly conserved during evolution.

Timothy Hunt is awarded for his discovery of cyclins, proteins that regulate the CDK function. He showed that cyclins were degraded periodically at each cell division as a part of the cell cycle control mechanism.


There are four different phases of the cell cycle. In the first phase (G1) the cell grows. When it has reached a certain size it enters the phase of DNA-synthesis (S) where the chromosomes are duplicated. During the next phase (G2), the cell prepares itself for division. During mitosis (M), the chromosomes are separated and segregated to the daughter cells. The cells are then back in G1 and the cell cycle is completed. CDK-molecules and cyclins drive the cell from one phase to the next. The CDK-molecules can be compared to an engine and the cyclins to a gear controlling in what model the engine will run.

It has been shown that genes for CDK-molecules and cyclins can function as oncogenes. CDK-molecules and cyclins also collaborate with the products of tumour suppressor genes (e.g. p53 and Rb) during the cell cycle. Increased levels of CDK-molecules and cyclins are sometimes found in human tumours, such as breast cancer and brain tumours, and thus have a diagnostic value. Using inhibitors of CDK-molecules is under clinical trial.

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