Practice question

Several biophysical methods probe protein interactions, but only Förster Resonance Energy Transfer exhibits steep distance dependence in 1-10 nanometer range. Efficiency proportional to inverse sixth power of separation imposes strict proximity requirement; beyond approximately 10 nm efficiency becomes negligible. SPR detects refractive index changes at surface, not molecular ruler scale; phage display selects binders; Co-IP isolates complexes regardless of distance. FRET therefore serves as spectroscopic ruler for conformational changes, domain interactions, and complex assembly within macromolecular dimensions near Förster radius.