About DNA work

Nobel prize for medicine awarded for work on ageing

Three scientists win the most prestigious prize in medicine for work on telomeres.

The Nobel prize for medicine goes to three researchers for their work on the ageing process, including Elizabeth Blackburn.

The discovery of a "protective cap" that prevents chromosomes from falling apart when cells divide has earned three American researchers this year's Nobel prize in medicine.

The award, announced at the Karolinska Institute in Sweden, honours Elizabeth Blackburn at the University of California, San Francisco, Carole Gredier at Johns Hopkins University, and Jack Szostak at Harvard University.

The three share the prize of 10m Swedish kronor (£818,000). It is the first time the Nobel prize for medicine has been awarded to two women at the same time.

The thread-like DNA molecules that carry genes are packed into chromosomes, the telomeres being the caps on their ends. Blackburn and Szostak discovered that a unique DNA sequence in the telomeres protects the chromosomes from degradation.

Greider and Blackburn identified an enzyme, telomerase, that makes the telomeres.

When cells divide, telomeres gradually become shorter and the cells age. But if the telomerase enzyme is very active, telomere lengths are maintained and cells are kept young. This is the process that occurs in cancer cells, which grow and divide without ageing.

Defective telomeras gives rise to a range of inherited diseases.

The discoveries had a major impact within the scientific community, and many scientists speculate that telomere shortening could be the reason for ageing.

The ageing process has since been found to be more complex and is now thought to depend on several different factors, the telomere being one of them.

Inherited diseases now known to be caused by telomerase defects include certain forms of a condition called "congenital aplastic anemia", in which insufficient cell divisions in the stem cells of the bone marrow lead to severe anemia. Certain inherited diseases of the skin and the lungs are also caused by telomerase defects.