Question

Which two tests are used to test for proteins and how do they work? ​

Answer 1

Biuret Test:

The compounds with peptide linkage undergoes this test. Proteins are polypeptides of amino acids linked together by peptide bonds. An alkaline solution of protein is treated with a drop of aqueous copper sulfate when a bluish violet colour is obtained.

Laboratory Test of Proteins 01

This test can be used for the identification of proteins and also for protein estimation. Biuret is the chemical product formed when urea is heated to 180oC. In this reaction two molecules of urea condense to form a bi-urea or biuret molecule. Biuret reagent in the presence of copper ions forms a violet colour complex.

Note: Formation of violet colouration confirms the presence of Proteins.

(b) Xanthoproteic Test:

Proteins on treatment with nitric acid gives a yellow or orange colour. Concentrated nitric acid is used for nitration. On the treatment of nitric acid, proteins give yellow precipitate which turns to orange colour on treatment with alkali.

Laboratory Test of Proteins 02

Note: The appearance of yellow colour solution confirms the presence of proteins.

(c) Millon’s Test:

Phenolic group of tyrosine of proteins react with mercuric sulfate in the presence of sodium nitrite and sulfuric acid to give red colour. Millon’s test is given by proteins containing phenolic amino acids. Gelatin does not give this test. First white precipitate is formed when proteins treated with millon reagent and turns to brick red on boiling confirms the presence of proteins.

Laboratory Test of Proteins 03

Note: The appearance of brick red colour solution confirms the presence of proteins.

Answer 2

Biuret test and the Ninhydrin test.

The biuret method is based on the fact that proteins (and, as a rule, all substances containing two or more peptidic bonds) react with copper to form a colored complex whose absorption (λmax=454 nm), in the presence of excess copper, is proportional to the amount of protein present.

Ninhydrin is a tricyclic 1,2,3-trione that acts as a reagent for amino acids. It's an organic chemical component that reveals hidden fingerprints on porous surfaces like paper, cardboard, and bare wood. Ninhydrin is a chemical that can be used to detect both primary and secondary amines.

Step-by-step explanation:

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