Green fluorescent protein (GFP) is found in jellyfish and emits green light when exposed to ultraviolet light. It can be genetically modified and used to label proteins and track infections in living organisms. GFP has a complex structure and has been used in various fields of biology, including neurology. GFP can also be modified to fluoresce in different colors. Controversially, genetically modified animals have been created to produce GFP, including fish, rats, pigs, and a rabbit.
Green fluorescent protein (GFP) is a protein found in a species of jellyfish, Aequorea victoria, found in the North Pacific. Fluorescence is a phenomenon whereby some substances absorb energy from electromagnetic radiation, such as light, and emit the energy at a different, usually longer, wavelength. The green glow produced by GFP comes from the fact that it absorbs relatively high energy blue and ultraviolet light and emits it as green light, which has a longer wavelength and less energy; then it will glow green when exposed to invisible ultraviolet light. GFP is of particular interest to biologists as, unlike most other fluorescent proteins, it fluoresces on its own without the need for any interactions with other molecules. Being a protein composed entirely of amino acids, this means that organisms can be genetically modified to produce it, giving rise to a wide range of applications in various fields of biology.
Bioluminescence occurs in many marine organisms. In the case of Aequorea victoria, a chemiluminescent substance called aequorin emits blue light when it combines with calcium ions. This light is then absorbed by the green fluorescent protein to produce a green glow. A number of other marine organisms have been found to contain these substances, but it is unclear why they evolved to produce this glow or to change color from blue to green. One suggestion, based on experimental evidence that incandescent GFP can release electrons, is that GFP could act as a light-activated electron donor, similar to chlorophyll in green plants.
Green fluorescent protein has a complex structure. The fluorescent part, known as the fluorescent chromophore, consists of three amino acids, tyrosine, glycine and serine or threonine, joined together in a ring shape. This is contained within a cylindrical structure that protects the chromophore from contact with other molecules, a key feature for fluorescence, as contact with water molecules would otherwise dissipate the energy used to produce the green glow.
GFP has proven to be extremely useful in fields such as genetics, developmental biology, microbiology and neurology. It can be used to label specific proteins within an organism in order to see where and when they are expressed; the part of the organism’s DNA that codes for the protein of interest can be engineered to also synthesize GFP, thus allowing the protein to be tracked within living cells using ultraviolet light. Viruses can also be labeled in this way, allowing infections in living organisms to be monitored. Green fluorescent protein can also be modified to fluoresce in many other colors, opening up new possibilities. One of them was the creation of transgenic mice with different combinations of fluorescent proteins expressed in neurons, which allow neural pathways in the brain to be studied in detail.
Other applications have been found outside biology. One controversial development is the engineering of fluorescent pets. Genetically modified animals have been created that produce green fluorescent proteins and include fish, rats, pigs and a rabbit.
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