Somatosensory receptors are divided into the major groups of receptors according to specific sensation: 

Mechanoreceptors (for touch and proprioception)

Thermoreceptors (for temperature)

Nociceptors (for pain or noxious stimuli)

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#Unit 13. Methods in Biology

Fluorescent probes are derived from a naturally occurring fluorescent protein, the green fluorescent protein (GFP) of the jellyfish Aequorea Victoria.

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#Unit 13. Methods in Biology

When excited by absorption of a photon of light, GFP emits a photon (that is, it fluoresces) in the green region of the spectrum. 

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#Unit 13. Methods in Biology

The light-absorbing/ emitting center of GFP (its chromophore) comprises an oxidized form of the tripeptide –Ser65–Tyr66–Gly67

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#Unit 13. Methods in Biology

This protein, from the bioluminescent jellyfish  Aequorea victoria, fluoresces with a peak wavelength of 508 nm (green light) when irradiated by ultraviolet or blue light (optimally 400 nm).

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#Unit 13. Methods in Biology

Cyclization between Ser and Gly is probably rapid, and the oxidation of the Tyr side chain (by O2) is probably the rate-limiting step of fluorophore generation.

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#Unit 13. Methods in Biology

Genetic engineering has introduced site-specific mutations that enhance fluorescence intensity and shift the wavelength of the emitted light to different colors, thereby making it possible to simultaneously monitor the expression of two or more different genes.