Practice question

Optimal FRET requires strong spectral overlap between donor emission and acceptor excitation, significant separation between excitation spectra to allow selective donor excitation, and separation between emission spectra to resolve signals. Cyan fluorescent protein and yellow fluorescent protein pair satisfies these criteria, with CFP emission around 475 nm overlapping YFP excitation around 514 nm. This combination provides high Förster radius approximately 4.9-5.2 nm, good quantum yield, photostability, and minimal cross-talk, making it standard for genetically encoded biosensors compared with GFP-RFP or other less optimized orientations.