Paul Charles Zamecnik was an American scientist who played a central role in the early history of molecular biology. Paul C. Zamecnik was born in Cleveland, OH in 1912. He attended Dartmouth College, where he majored in chemistry and zoology and graduated with a bachelor's degree in 1933. He then went Harvard Medical School, received his M.D. in 1936, and served his residency at Harvard from 1936 to 1938 and interned at the University Hospitals in Cleveland until 1939. Zamecnik continued to work on tRNA purification and sequencing. Then in 1978, he made another interesting observation. He found that oligonucleotides were able to enter cells. This led to a new area of research and possible therapy. Anti-sense RNA could be used to block the translation of viral messenger RNA. From 1993, Zamecnik was on the Board of Directors of a biotech company called Hybridon Inc. that develops therapeutic drugs based on the idea of anti-sense blockers. He received the National Medal Of Science in 1991.