What does the positive result of the biuret test signify?

A positive result of the biuret test signifies the presence of peptide bonds, which are indicative of proteins. The biuret reagent contains copper sulfate, which reacts with peptide bonds, forming a colored complex. This reaction is specific to proteins and polypeptides due to their unique structure that includes these bonds.

Since the biuret test is particularly designed to detect proteins rather than smaller molecules or other biochemical structures, it does not react to the presence of glucose, fatty acids, or even free amino acids unless they are part of a larger protein structure. To summarize, the significance of a positive biuret test lies in its ability to confirm the existence of protein molecules defined by their peptide bonds.