Classification of amino acids,Structure of Protein


Classification of amino acids

Amino acids are classified as acidic, basic or neutral depending upon the relative number of amino and carboxyl groups in their molecules. Same no. of amino and carboxyl teams makes it neutral, more no. of amino than carboxyl groups makes it basic and more carboxyl teams as compared to amino teams makes it acidic.

Amino acids  that can be synthesised in the body are known as non-essential amino acids. E.g. Glycine, alanine on the other hand, those which cannot be synthesised in the body and must be obtained through diet are called essential amino acids. e.g. valine.


Proteins are high molecular weight nitrogen containing complex organic compounds. Amino acids are basic units of protein. These are abundantly present in animals and plants. Egg, milk, cheese, fish, meat, etc. are main source of animal protein. Pulses, cereals, pea, beans, groundnuts and soybeans are main sources pf plant protein.

Zwitter ion

In aqueous solutions, the amino group can lose a proton and amino group can accept a proton, giving rise to a dipolar ion called zwitter ion.

Structure of proteins

On the basis of their molecular shape, these are two types-

Fibrous protein– When the polypeptide chains runs parallel and are help together by hydrogen and disulphide bonds, a fibre like structure is formed . Such proteins are insoluble in water . e.g. keratin, myosin.

Globular proteins– When the chains of polypeptides coil around to give a spherical shape the protein is called a globular protein. Such proteins are usually soluble in water. e.g. insulin, albumin.

On the basis of structure, proteins have four main structures

Primary structure– When each polypeptide in a protein linked in a specific sequence of amino acids, we call them primary structure.

Secondary structure-  Secondary Structure refers to the shape in which a long polypeptide chain exist. They are found to exist in two different types of structures -helix and -pleated sheet.

Tertiary structure– This structure represents the over all folding of the polypeptide chains.

Quaternary Structure– Some proteins are made of two or more polypeptide chain and have different spatial arrangements. Such structure in of proteins is known as quaternary structure.

Denaturation of proteins– Due to temperature change or pH change k secondary and tertiary destroyed but primary structure remains intact. This process is called denaturation of proteins.

Enzyme– These are high molecular weight complex organic compounds. These are actually proteins. These are produced in living cells and catalysed the reactions occurring in them, so also called bio-catalyst. E.g. zymase, etc.

Lipids– That particular group biomolecules is called lipids which are insoluble in water but are soluble in organic solvent like ether, acetone, etc.


Functions of lipid

  1. In the form of a structural component of cell membranes.
  1. In the storage of energy return.
  1. In the form of emulsifier.
  1. In the form of metabolic fuel.


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Rose glan
Rose glan

Soo easy and good notes