Question

D. Color Tests for Proteins n on Observations of Color Tests Sample 1. Biuret 2. Ninhydrin Glycine 3. Xanth 2. Xanthoproti Tyrosine Gelatin Egg albumin Casein (milk protein) Questions and Problems Q5 After working with HNO,, a student noticed that she had a yellow spot on her hand What might be the reason? 06 Which samples give a negative biuret test? Why? Q7 What functional group gives a positive test in the xanthoproteic test? 08 What tests could you use to determine whether an unlabeled test tube contained an amino acid or a protein?

Answer 1

Biuret test: Only peptides give this positive test. Because the peptide forms complex with Cu2+ ions to give pale-purple color to the solution. Ninhydrin test: Amines such as a-amino acids react with ninhydrin to give a blue-purple colored product. secondary amine like proline gives yellow-orange colored product. Xanthoproteic test: This is used to detect amino acids containing an aromatic amino acids such as tyrosine, tryptophan and phenylalanine in a protein solution which gives yellow color nitro derivatives on heating with conc. HNO3. Biuret Ninhydrin Xanthoproteic Glycine -ve +ve -ve Tyrosine -ve +ve +ve Gelatin +ve +ve +ve Egg albumin +ve +ve +ve Casein +ve +ve +ve Q5) On our hands there are some aromatic ring containing protines present and hence they give a yellow color. Q6) Only peptides containing compound give +ve Biuret test hence Glycine and Tyrosine gives -ve test. Q7) Aromatic ring containing amino acids or protines give +ve Xanthoproteic test. Q8) Biuret test is able to differentiate amino acids and protines.