Protein & its Tests | Chemistry for JAMB PDF Download

Introduction

Proteins are macromolecules composed of amino acids, which play crucial roles in various biological processes. Understanding the primary structure, hydrolysis, and identification tests for proteins is essential in the study of chemistry. This note will provide a concise overview of these topics in accordance with the JAMB Chemistry Syllabus.

I. Primary Structures of Proteins

Amino Acids

• Proteins are composed of a variety of amino acids, which are organic compounds containing an amino group (-NH₂) and a carboxyl group (-COOH).
• Amino acids are classified into essential and non-essential types, based on whether the body can synthesize them or not.

Peptide Bonds

• The primary structure of proteins is determined by the sequence of amino acids connected by peptide bonds.
• A peptide bond is formed when the carboxyl group of one amino acid reacts with the amino group of another, resulting in the release of water molecules.

Polypeptides

• Polypeptides are long chains of amino acids joined together by peptide bonds.
• The sequence and arrangement of amino acids in a polypeptide chain determine the protein's primary structure.

II. Hydrolysis of Proteins

Definition

• Hydrolysis is a chemical reaction that breaks down proteins into their constituent amino acids by the addition of water molecules.
• It is facilitated by enzymes called proteases or by acid or alkaline hydrolysis.

Acid Hydrolysis

• In acid hydrolysis, proteins are heated in the presence of a strong acid, such as hydrochloric acid (HCl), under controlled conditions.
• The proteins are broken down into amino acids.

Alkaline Hydrolysis

• Alkaline hydrolysis involves the treatment of proteins with strong bases, such as sodium hydroxide (NaOH), at elevated temperatures.
• This process also breaks proteins down into their constituent amino acids.

III. Tests for Proteins

1. Ninhydrin Test

• The ninhydrin test is used to detect the presence of amino acids and proteins.
• When ninhydrin reacts with amino acids, it forms a purple-colored complex.
• The intensity of the color produced is directly proportional to the concentration of amino acids or proteins.

2. Biuret Test

• The biuret test is employed to identify the presence of peptide bonds in proteins.
• When copper(II) ions react with peptide bonds in an alkaline medium, a violet or purple color is observed.

3. Millon's Test

• Millon's test is specifically used to detect the presence of phenolic compounds in proteins.
• When proteins are treated with Millon's reagent (mercuric nitrate in nitric acid), a red precipitate or solution indicates the presence of phenolic compounds.

4. Xanthoproteic Test

• The xanthoproteic test is performed to identify proteins containing aromatic amino acids, such as tyrosine and phenylalanine.
• When proteins are treated with concentrated nitric acid, a yellow color develops, which intensifies upon the addition of sodium hydroxide.

Conclusion

Understanding the primary structure, hydrolysis, and tests for proteins is essential for a comprehensive understanding of chemistry. The knowledge gained from studying these topics enables us to analyze and identify proteins in various biological systems.