Carol W. Greider received one-third of the Nobel Prize in Physiology or Medicine for "the discovery of how chromosomes are protected by telomeres and the enzyme telomerase." Working as a graduate student with her supervisor and fellow prize recipient Elizabeth H. Blackburn, Greider made the groundbreaking discovery that the formation of telomere DNA was due to the activity of an enzyme they later called telomerase. Greider and Blackburn then purified the enzyme and showed that it consists of RNA as well as protein. These discoveries explained how the ends of the chromosomes are protected by the telomeres and that they are built by telomerase. Over the years, Greider’s continued work in characterizing telomeres and telomerase further highlighted the importance of this RNA- and protein-containing enzyme complex in maintaining genetic stability.