Amino Acids and its Types

 Amino acids and its types

Definition and General Formula

Amino acids are the basic building blocks of proteins. Amino acids are bifunctional (polyfunctional) organic acids having both an acidic carboxyl group (-COOH) and a basic amino group (-NH₂ or >NH) along with distinct side chain R (which is different for different amino acids). Almost all the naturally occurring amino acids are a-amino acids in which amino group is attached to a-carbon atom (relative to the carboxyl group). They have following general formula:

    

Where R may be hydrogen, a straight or branched chain alkyl group or an aryl group.

The amino group in amino acids may be present at any carbon atom other than that of carboxyl group containing carbon (i.e. a– carbon). Based on whether the amino group is present on the a, β or γ - carbon atom relative to the carboxyl group, amino acids are referred to as a, β and γ–amino acids respectively.  

Bio-medical Importance of Amino Acids

1.	Protein synthesis
2.	Hormones synthesis
3.	Energy Source
4.	Regulation of metabolism

Types of Amino Acids based on their acidity or alkanity

1.	Neutral amino acids	;	contain one –NH2 & one –COOH group.	e.g.	Glycine, alanine, Valine, Leucine
2.	Acidic amino acids	;	contain more than one –COOH groups.	e.g.	Aspargine, Glutamine
3.	Basic amino acids	;	contain more than one –NH2 groups	e.g.	Lysine, Arginine.

Essential Amino acids and Non-essential Amino Acids

About 20 amino acids have been identified as the constituents of most of the animal and plant proteins. Out of 20 amino acids which are required for protein synthesis, the human body can synthesize only 10 and such amino acids are called Non-essential amino acids. e.g. Glycine, alinine, proline, aspartic acid, glutamic acid, tyrosine, serine, cysteine, aspargine.

The ten amino acids that are not synthesized by human body and hence are needed to be provided in the diet for proper health and growth are called Essential Amino Acids. [They are 10 for infants and 8 for adult human being]. They include Valine, Leucine, Isoleucine, Lysine, Methionine, Threonine, Arginine, Tryptophan, Phenylalanine, and Histidine (last two are needed for infants).

Zwitterion

The dipolar but overall electrically neutral charged ion with positive as well as negative ends within the same molecule is termed as Zwitterion (German; two ions). The dipolar ionic structure is also called internal salt. All a–amino acids exist largely as dipolar ionic forms or Zwitterions in solution that is formed when the proton goes from the acidic carboxylic group (on ionization) to basic amino group (Lewis base).

 

Due to the Zwitter ions form, amino acids are soluble in water but insoluble in organic solvents. The Zwitterion formation makes amino acids amphoteric and allows them to donate or accept proton from the medium or solvent in which they are dissolved.

Peptide Linkage

The acid-amide (-CO -NH -) bond through which amino acids are linked in proteins by eliminating a water molecule is called Peptide Linkage. This linkage is formed by the removal of a water molecule b/w an -NH₂ group of an amino acid and -COOH group of another. The product formed from condensation of two amino acids containing a single peptide linkage is called Dipeptide. The product formed from condensation of three amino acids containing two peptide bonds is called Tripeptide.