Question

You did an experiment in your class room to test the proteins in that
a) What apparatus you used in the experiment.
b) What are the solution you prepared
c) What change you observed in the colour
d) What precautions you take in this experiment. .​

Answer 1

Answer:

The following are the tests carried to find the presence of proteins in a given sample.

Biuret test

Xanthoproteic test

Millions test

Ninhydrin test

(a) 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.



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.



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.



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

(d) Ninhydrin Test:

Proteins reacts with pyridine solution of ninhydrin gives coloured solution from deep blue to violet pink sometimes even red colour in some cases. Ninhydrin solution is prepared by dissolving 0.1gm of ninhydrin in about 100ml of distilled water. But this solution of ninhydrin is unstable and can be kept for two days.

The chemical reaction is given below.



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