Types of Amino Acids with Definition and Classification

What are amino acids?

Amino acids are carboxylic acids having amino groups. the most important types of amino acids are the α-amino acids, having the general formula.

Amino acid Structure &  Formula 

amino acid formula

hundreds of amino acids are possible, but only twenty are found in proteins and all of these α-amino acids.

Types of amino acids

  • Those having amino (-NH2) group on alpha (α) are called α-Amino acids.
  • Those having amino (-NH2) group on beta (β) are called β-Amino acids.
  • Those having amino (-NH2) group on gamma (ϒ) are called ϒ -Amino acids.

Essential Amino acids

These are the amino acids, which cannot be synthesized in our body but they are essential for:

  • The growth of infants.
  • Transmission of impulses in the nervous system.

Their deficiency results in many diseases. They must be added to our body through our diet. Examples are:

  1. Leucine
  2. Iso-Leucine
  3. Methionine
  4. Threonine
  5. Arginine
  6. Valine

About 10 Amino acids are essential.

Classification of Amino Acids

Amino acids have been classified according to their natural, acidic or basic nature.

Neutral Amino acids

These exhibit amphoteric nature. They contain one basic (-NH2) and one acidic (-COOH) group.

neutral amino acids

Acidic Amino Acid

They exhibit acidic nature. They contain one basic (-NH2) group and more than one acid (-COOH) groups.

structure of Aspataric acid

Basic Amino acids

neutral amino acids

They exhibit basic character. They contain one acidic (-COOH) group and more than one basic Amino (-NH2) groups.

Zwitterion (Dipolar nature)

A dipolar charged but overall electrically neutral ion is called Zwitterion. In an amino acid, carboxylic (-COOH) group ionizes to donate a proton (H+), whereas amino (-NH2) group with a lone pair of electrons behaves as proton accepter i.e. Lewis base. Hence amino acid exists more as dipolar ion i.e. Zwitterion than in an unionized form.

zwitterion amino acids

The most important reaction of the amino acid is the formation of peptide bonds and this is possible because amino groups of one acid can react with a carboxylic group of another and vice versa.

Although there is only one peptide bond in the above compound, it is called a dipeptide.

Role of Amino acids in the Human body

The role of Amino acids in the human body is as follows:

  1. Amino acids may be synthesized back into protein.
  2. Oxidation may take place to provide energy.
  3. If the diet is low in carbohydrates or fats, body protein may be transformed into either of these or used to make hormones and other body necessities.


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