Practice question

Coomassie Brilliant Blue G-250 and R-250 are triphenylmethane dyes that bind non-covalently to proteins through combined electrostatic attraction to protonated amine groups of lysine, arginine and histidine and hydrophobic interactions with aromatic residues phenylalanine, tyrosine and tryptophan. Binding shifts absorption maximum from 465 to 595 nanometers, producing intense blue color proportional to protein amount, forming basis for Bradford assay. It does not efficiently intercalate DNA base pairs, bind RNA or stain polysaccharides, unlike ethidium bromide, SYBR Green or periodic acid-Schiff reagents. This specificity underlies both gel staining and solution quantification.