CAM, FRET [forster resonance energy transfer], chromophore, ROGER [Victor, Clarence], M13, These virtual photons are undetectable, since their existence violates the conservation of energy and momentum, and hence FRET is known as a radiationless mechanism Cameleon is an engineered protein based on variant of green fluorescent protein used to visualize calcium levels in living cells. It is a genetically encoded calcium sensor created by Roger Y. Tsien and coworkers.[1] The name is a conflation of CaM (the common abbreviation of calmodulin) and chameleon to indicate the fact that the sensor protein undergoes a conformation change and radiates at an altered wavelength upon calcium binding to the calmodulin element of the Cameleon. Cameleon was the first genetically encoded calcium sensor that could be used for ratiometric measurements and has found many applications in neuroscience and other fields of biology. It was created by fusing BFP, calmodulin, calmodulin-binding peptide M13 and EGFP.[2] Mechanism [edit] The DNA encoding cameleon fusion protein must be either stably or transiently introduced into the cell of interest. Protein made by the cell according to this DNA information then serves as a fluorescent indicator of calcium concentration. In the presence of calcium, Ca2+ binds to M13, which enables calmodulin to wrap around the M13 domain. This brings the two GFP-variant proteins closer to each other, which increases FRET efficiency between them. Förster resonance energy transfer (FRET), Fluorescence resonance energy transfer (FRET), resonance energy transfer (RET) or electronic energy transfer (EET), is a mechanism describing energy transfer between two chromophores.[1] A donor chromophore, initially in its electronic excited state, may transfer energy to an acceptor chromophore through nonradiative dipole–dipole coupling.[2] The efficiency of this energy transfer is inversely proportional to the sixth power of the distance between donor and acceptor making FRET extremely sensitive to small distances.[3] Measurements of FRET efficiency can be used to determine if two fluorophores are within a certain distance of each other.[4] Such measurements are used as a research tool in fields including biology and chemistry. FRET is analogous to near field communication, in that the radius of interaction is much smaller than the wavelength of light emitted. In the near field region, the excited chromophore emits a virtual photon that is instantly absorbed by a receiving chromophore. These virtual photons are undetectable, since their existence violates the conservation of energy and momentum, and hence FRET is known as a radiationless mechanism. Quantum electrodynamical calculations have been used to determine that radiationless (FRET) and radiative energy transfer are the short- and long-range asymptotes of a single unified mechanism.[5][6] A chromophore is the part of a molecule responsible for its color. [1] The color arises when a molecule absorbs certain wavelengths of visible light and transmits or reflects others. The chromophore is a region in the molecule where the energy difference between two different molecular orbitals falls within the range of the visible spectrum. Visible light that hits the chromophore can thus be absorbed by exciting an electron from its ground state into an excited state. In biological molecules that serve to capture or detect light energy, the chromophore is the moiety that causes a conformational change of the molecule when hit by light.
Posted on: Fri, 14 Jun 2013 15:17:48 +0000
Trending Topics
Recently Viewed Topics
© 2015