Genetic engineering and more fluorescence...

Asaad asks a really good question about the safety of sticking random genes into people. To be honest, I can’t give you a definite answer about whether sticking GFP into a human would be harmful or not because, as far as I know, it has never been tried. One major ethical concern about genetic engineering in humans is that we can’t be 100% certain what sticking a gene into a person would do until we actually do the experiment. This is less of a problem for conventional pharmaceuticals, because you can recruit volunteers who are informed about the risks. But a person who isn’t even born yet obviously isn’t around to make that sort of decision! A person who has been genetically engineered would be stuck with that for the rest of his or her life. And you are right that the children of that person could inherit the gene. (They would probably have a 50% chance of inheriting it if it was carried on one of the parent’s chromosomes.) Whether or not it would ever be justified to make that sort of decision for someone is a very serious ethical question! All that said, though, my guess is that GFP would probably be safe to have floating around inside your cells. As far as we can tell, it doesn’t seem to do much of anything (aside from glowing) when you stick it into the cells of other organisms. So there isn’t any reason to think that it would be harmful…though it probably isn’t work risking it just for fun! As for how fluorescence works…that’s a really cool story. You may have talked a bit about atoms in one of your science classes. If you remember, atoms are made of nuclei (made of positively-charged protons and uncharged neutrons) orbited by negatively-charged electrons. The electrons are in things called orbitals. You can think of an orbital as like a “cloud” of electrons with a particular shape. (If you study quantum mechanics someday, you’ll learn that electrons in orbitals can be thought of as waves too…that’s a weird thing to think about!).

Well anyway, atoms can combine in different ways to form molecules. When this happens, the electron orbitals from all the individual atoms fuse into new orbitals called molecular orbitals. When the molecule is just hanging out (i.e. when the light is off), those electrons are generally in the lowest-energy orbitals possible. However, when a particle of light (a photon) with the right energy interacts with the electrons, they can absorb the energy in the photon and jump up to a higher-energy orbital. The molecule is in what is called an excited state. However, this excited state is unstable. Think of it as sort of like a pencil balanced on its tip. Maybe the molecule can exist in that state for a split second, but it wants to get back to its ground state. In some molecules, the electron just falls back to its low-energy state and the energy from the light is lost as heat. But in some special molecules (like the molecules of the fluorescein that I brought you), something really cool happens where the molecule emits a new particle of light when the electron falls from its excited state back down to its low-energy state. This is the light that you observe as fluorescence. The new photon of light is a different color than the original photon of light because some of the energy is typically lost in the process of kicking the electron up to a high-energy state and letting it fall back down again. I hope that wasn’t too unclear! Let me know if you have any more questions!

Note: 1 nanosecond = 1/1,000,000,000 second
1 picosecond = 1/1,000,000,000,000 second
1 femtosecond = 1/1,000,000,000,000,000 second!!!!!!

What's really crazy is that people have figured out ways to observe things this fast! One of the people who figured out how to do this won the Nobel Prize. See: http://nobelprize.org/nobel_prizes/chemistry/laureates/1999/illpres/