From The New York Times:
Looking at a cell through an optical microscope is like a satellite view of New York City. You can see Central Park, buildings, streets and even cars, but understanding the cultural and economic life of the city from the distance of Earth orbit is difficult, maybe impossible. Likewise, biologists can easily see large structures inside a cell like the nucleus with its folded-up chromosomes and the energy factories of the mitochondria. But most of the details of how a cell functions — the locations of specific proteins, the mechanisms used by the cell to send messages back and forth, the transportation system that moves proteins from place to place — were too small to be seen.
Nowadays, using the same optical microscopes, biologists can see what was once invisible with the help of a fluorescent protein that is the focus of this year’s Nobel Prize in chemistry. The prize was awarded to Osamu Shimomura of the Marine Biological Laboratory in Massachusetts and Boston University, Martin Chalfie of Columbia University and Roger Y. Tsien of the University of California, San Diego. The protein, known as the green fluorescent protein, or G.F.P., was for years just a biological curiosity from a glowing jellyfish. It was found in the summer of 1961 when Dr. Shimomura, then a researcher at Princeton, and Frank Johnson, a Princeton biology professor, collected 10,000 Aequorea victoria jellyfish in the waters off Friday Harbor in Washington State. They were looking for what made the jellyfish glow at its edges, and from the 10,000 jellyfish they extracted aequorin, a bioluminescent protein that flashes blue when it interacts with calcium.
More here.