Practice question

Biotin-labeled nucleic acid probes are visualized through exceptionally strong non-covalent protein interactions. Avidin, a tetrameric glycoprotein from egg white, and streptavidin from Streptomyces avidinii bind biotin with a dissociation constant near 10^-15 M, among the strongest known biological affinities. This stability allows efficient capture of biotinylated probes followed by detection using enzyme-conjugated or fluorophore-conjugated avidins. Amplification steps improve sensitivity in blots and histochemistry. Antibodies, alkaline phosphatase, and T4 ligase do not exhibit specific high-affinity biotin binding, making avidin-streptavidin essential for indirect non-isotopic detection systems.