Final answer:
Glycine and tyrosine produce negative Biuret tests because they do not contain the peptide bonds needed to form the violet-colored complex with copper(II) ions.
Step-by-step explanation:
Glycine and tyrosine produce negative Biuret tests because they do not contain the peptide bonds needed to form the violet-colored complex with copper(II) ions, which is indicative of protein presence. The Biuret test is a common method to test for the presence of proteins and relies on the reaction between peptide bonds and copper(II) ions. Since glycine and tyrosine do not have peptide bonds, they do not form the violet complex, resulting in a negative test.