LIFE SCIENCE

Detailed explanation-1: -The biuret reaction is based on the complex formation of cupric ions with proteins. In this reaction, copper sulfate is added to a protein solution in strong alkaline solution. A purplish-violet color is produced, resulting from complex formation between the cupric ions and the peptide bond.

Detailed explanation-2: -Note: The biuret reaction is typically used to indicate the presence and concentration of protein in a test sample and occurs when the peptide bonds in a protein react with the copper ions to produce a violet or purple complex. The intensity of color in solution is proportional to the number of peptide bonds.

Detailed explanation-3: -Biuret test It is based on the biuret reagent, a blue solution that turns violet upon contact with proteins, or any substance with peptide bonds. The test and reagent do not actually contain biuret; they are so named because both biuret and proteins have the same response to the test.

Detailed explanation-4: -Proteins give a purplish violet colour while proteoses and peptones give a pink colour. Peptides give a very light pink colour and gelatin gives a blue colour.

Detailed explanation-5: -The reason behind this colour is the formation of a chelate complex or the copper coordination complex. Cu (II) or cupric ions create a chelate complex of violet colour, using oxygen of water and the unshared electron pairs of peptide nitrogen. Since this complex absorbs light in 540 nm, it appears violet.