The Nobel Prize in Physiology or Medicine 2009 is awarded to Elizabeth H. Blackburn, Carol W. Greider and Jack W. Szostak for their discoveries on the structure and function of telomeres at chromosome ends and the enzyme telomerase. The first results were based on utilizing single cell organisms in the experiments, but later on it turned out that the biochemical systems are conserved in evolution. The findings of the Nobel Laureates included explanation of two biological problems related to the linear structure of chromosomes, on how chromosomes are protected from degradation and how the ends of chromosomes are replicated. Repeats in the DNA sequence at the telomeres are fundamental for their function. The enzyme telomerase is extraordinary since it contains a RNA component in addition to the protein catalytic unit. Its activity is classified as reverse transcriptase, since it utilizes RNA as a template for DNA synthesis. The history of the major discoveries will be adressed in the seminar, aswell as the structure and function of telomeres and telomerase and the importance of this new knowledge for understanding biochemical pathways within the cell and human diseases.