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Carol W. Greider

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Carolyn Widney Greider is a prominent American molecular biologist. She is a Distinguished Professor at the University of California, Santa Cruz. Greider is most famous for discovering telomerase, a vital enzyme in living cells. This discovery earned her the 2009 Nobel Prize in Physiology or Medicine. She shared this honor with Elizabeth Blackburn and Jack W. Szostak. Her work has provided deep insights into how cells age and how they can become diseased.

To understand Greider's work, one must understand chromosomes. Chromosomes are structures that hold genetic information. At the very ends of these chromosomes are protective caps called telomeres. Telomeres consist of specific DNA sequences, such as a six-base pair motif. During DNA replication, the cell copies its genetic code to divide. However, this process causes the telomeres to shorten slightly each time. Without protection, chromosomes would eventually deteriorate. This shortening can lead to senescence, which is when cells stop dividing. It can also cause cancer-causing chromosome fusion.

Greider discovered how cells prevent this deterioration. She identified an enzyme called telomerase, which was originally named telomere terminal transferase. Telomerase acts as a rebuilding tool for the chromosome tips. It adds extra DNA bases to the ends of the telomeres. This mechanism determines the lifespan of a cell. Greider found that telomerase uses an RNA component as a template. She proved this by using RNA degrading enzymes in her research. When the RNA was removed, the telomeres stopped extending. This showed that the enzyme relies on RNA to build the DNA repeats.

Greider's discovery happened while she was a graduate student at the University of California, Berkeley. She worked in the laboratory of Elizabeth Blackburn. They chose to study a model organism called Tetrahymena thermophila. This is a small, single-celled protozoan that lives in fresh water. It was an unusual choice, but it has a large number of telomeres to study. On December 25, 1984, Greider obtained results that suggested a specific enzyme was responsible. After six more months of research, the discovery was confirmed. They published their major findings in the journal Cell in December 1985.

Since her initial discovery, Greider has expanded her research into many different systems. In 1989, she cloned the gene for the RNA component in Tetrahymena. She later showed that telomerase is processive, meaning it can add multiple repeats in one go. In 1990, she worked with Calvin Harley to link telomere shortening to cellular senescence. She also studied how telomeres behave in yeast, specifically Saccharomyces cerevisiae. In these yeast cells, she found that short telomeres trigger a DNA damage response. This research helps scientists understand the fundamental rules of cell biology across different species.

Greider has also conducted significant research using mice to study human-like biology. In collaboration with Ronald A. DePinho, she produced the first telomerase knockout mouse. A knockout mouse is an organism where a specific gene has been made inoperable. This allowed scientists to see what happens when telomerase is missing. The results showed that while telomerase is not strictly required for life, its absence causes problems. These mice showed various deleterious phenotypes, often called premature aging. Greider even observed that by the sixth generation, these mice became entirely sterile.

Greider's journey to scientific success included personal challenges. She has dyslexia, a condition that affects how the brain processes written language. This made standardized tests, like the GRE, difficult for her. She applied to thirteen different graduate schools but was only accepted by two. These were the California Institute of Technology and UC Berkeley. Greider chose Berkeley, and her dyslexia eventually became a scientific asset. She credits her ability to intuit complex, simultaneous processes to her compensatory skills. This unique way of thinking helped her make unusual and successful decisions in her career.

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