What indicates the presence of peptide bonds in the biuret test?

The biuret test is a biochemical test used to detect the presence of peptide bonds, which are indicative of proteins. When a solution containing proteins is treated with biuret reagent, which contains copper sulfate, a reaction occurs. Specifically, if peptide bonds are present, the copper ions interact with these bond structures, resulting in a characteristic color change.

The correct answer indicates that a change in color to violet occurs. This color change takes place due to the formation of a complex between the copper ions and the peptide bonds, signaling the presence of proteins. This violet coloration is a definitive indicator in the biuret test, demonstrating that proteins, which are made up of amino acids linked by peptide bonds, are present in the tested sample.