Protein coagulation and the biuret test

ChemistryBiomolecules & PolymersAges 17–18

Five test tubes of egg-white solution are heated or treated with HCl, ethanol and CuSO₄, and the fifth undergoes the biuret test (NaOH + CuSO₄). Students see the protein coagulate into a white solid or precipitate and the biuret tube turn violet; switch the sample to a tripeptide, dipeptide, glycine or glucose to see that only molecules with at least 2 peptide bonds give the violet color. A results table records the observation and explanation for each tube.