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The jellyfish Aequorea Victoria creates a protein (GFP) that, when illuminated with blue light (l = 395 nm emits green light (l = 508 nm The gene for producing GFP is known and can be inserted into any cell and attached to the gene that creates any other protein we might be interested in. So the when the cell builds the protein of interest, it attaches a GFP "tag" to it. The protein of interest can then be tracked in the living cell. One way this conversion of frequencies could work is the following:

1. The blue light is less energetic than the green light. The blue photon scatters off a protein and extracts energy from it, coming out green.
2. The blue light is more energetic than the green light. The blue photon is absorbed by the protein, which then goes into a highly excited state. It decays back to the ground state in two stages, going through an intermediate excited state and emitting two photons of smaller energy, one of which is green.
3. The protein acts as a prism, changing the wavelength of the blue light as it moves through the protein, stretching it into green light.
4. The energy is not the relevant quantity. The blue light has a higher frequency than the green light. The blue light sets some of the electrons in the protein oscillating at a high frequency. The lower frequency is excited in conjunction with it in the way that a crystal goblet, rung by a pure tone, vibrates with other associated tones.
5. None of the above.

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Page last modified October 31, 2002: MP09