What are Proteins? [Updated] Structure and classification of Proteins

Technically these are macromolecules are formed when amino acid unit link together. These are very essential for living organism. Proteins are involved in many chemical processes and have great nutritional value.

In 1838 Jons Jacob introduced the term. The word, “Proteins” derived from Greek word “Proteios”. These are specific specie to specie. These are species and organ specific. Approx 20 different amino acid naturally occurs in nature.

Proteins which have same function will have same structure as well. The human body contains 10000 different kinds of proteins. Proteins sequence could be find out using Expasy Translate Tool.

Plant can synthesize amino acids but animals cannot do so. After reading this article you will able to know about structure, properties & sources as well as you will know about zwitter ion & whey protein.

Peptide and Proteins

The compound formed by condensation of two or more same or different amino acids is called peptides. They contain –CO-NH- bond in their structure.

It is called peptide bond or peptide linkage. The bond formed between carbonyl group of one amino acid and formed between carbonyl group of one amino acid and amino group of other amino acid with elimination of water molecule is called peptide bond.


Two molecules of amino acids join and form dipeptide three molecules of amino acids join and form tri peptide. A long number of amino acids join by peptide bonds and form a polypeptide. A peptide having a molecular mass up to 10,000 is called polypeptide.

A Peptide having molecular mass more than 10,000 is called protein. The human body contains at least 10,000 different proteins. They are present in skin, hair, muscles and non-bony tissue of body. The structure of polypeptide and protein is given below.

Structure and Properties

According to Biochemistry Study, Amino acid composition of Protein are consist of long chain of alpha α- amino acids. α- amino acids mean that carbon of amino acid consist of amino group (−NH2) , carboxyl group and any alkyl group

Acid nature of Amino Acid

In case of acidic condition pH is less than 4 and –COO group combine with hydrogen atom and converted in to –COOH group which is uncharged.

Alkali Nature of Amino Acid

In case of alkali condition pH is remaining above 9 the amino group (−NH+3) release hydrogen ion and converted in to (−NH2).

What is Zwitter Ion?

Molecule of amino acid consists of dipolar ions. Amino acid carries both positive and negative charge and do not migrate with electric field.

More then 100 amino acid found in nature but 20 types of amino acids are found in.

How Protein Molecule is formed?

Alpha- amino acid linked together through peptide bond and long chain of molecule is formed.

What is Peptide Bond?

Peptide bond is formed between amino group of amino acid and carboxyl group. When three amino acids are join together yield tripeptied.

When we talk about its structure we discussed as N- terminal or free alpha amino acid found at left side and C terminal ore free carboxyl group found at right side.

These molecules are joined through peptide bond. They are basically macromolecules. Many amino acids are linked and form a structure of protein.

More than 100 amino acids linked to each other in a long peptide chain.

Classification of proteins

On the basis of physico – chemical properties Proteins have three classes.

  1. Simple Proteins
  2. Compound Proteins
  3. Derived Proteins

Simple Proteins

On Hydrolysis Proteins yields amino acids and their Derivatives called simple proteins. e.g. collagen, globulins. legumin, albumins. Globulins are found in animals. This is insoluble in water but soluble in dilute salt solution. Lactoglobulins is found in body muscles. The legumin and collagen are present in connective tissues of body. They are the mass abundant proteins and form 25 to 35% of body protein.

Compound or Conjugate proteins

In these type molecules attached with some non – Proteins group called conjugate proteins. Phospho – Proteins are conjugate with Phosphoric Acid. Lipoproteins are conjugated with Lipids. ( Cholesterol , Lecthin )

Derived Proteins

These are derived from simple and conjugate proteins. e.g Peptones, Polypeptides, Oligopeptides.

Protein Sources

Are found through meat, vegetables, poultry, egg all sea food, soy products seed and nuts etc.

Alternative Sources

There are several alternative sources like whey and soy hump. Its benefits are meet to that person who exercises because whey proteins are better for regenerating muscles & mass.

What is Whey Protein?

Whey protein is by- product of cheese making. It will found through protein powders.

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