We know that all the biological activities are dependent on the biological molecules which are found in the living bodies. These Biomolecules are responsible for different activities such as reproduction, movement etc. In this article we will discuss about one of the biological molecules which are named as protein. They are composed of similar monomer units which are called amino acids. They are organic molecules which are made up of carbon, hydrogen, oxygen, nitrogen and some heteroatom like sulphur etc.
Amino acids involve in peptide linkage to form polypeptide chains. The amino acids molecules contain one –NH2 and one –COOH group on the same carbon atom. This carbon atom is called as alpha carbon atom and amino acids are called as alpha amino acids. In living bodies, only alpha amino acids involve in the formation of polypeptide chains or proteins. The amino group and carboxyl group of the molecule involve in the condensation reaction to form amide bond with other molecules.
The condensation reaction involves the elimination of water molecule in each step. The sequence of amino acids in the polypeptide chains is called as primary structure of proteins which further being complicated to form secondary structure. Two possible secondary structures are alpha helical and beta plated forms in which polypeptide chains are oriented in helical or plated form with the help of H-bonds. There are 20 amino acids in the human beings which are bonded with each other in different sequences to form polypeptide chains. These 20 amino acids can be classified in different manners such as on the basis of structure or polarity or side chains. On the basis of side chain of the amino acids; they can be classified as acidic, basic and neutral amino acids. The acidic amino acids contain some acidic functional group in the molecule such as carboxyl group. The example of acidic amino acids is glutamic acid, aspartic acid etc.
The basic amino acids contain some alkaline functional group in the side chains such as amino group, amido group etc. in glutamine, asparagine. The presence of hydrocarbon chain in the side chain of makes the molecule neutral as one amino and one carboxyl group does not impart any acidic or alkaline nature to the molecule.
The amino acid molecule is usually existed in the form of Zwitter ion in which two opposite charges are found on the same carbon atom. Since basic amino group exits as –NH3+ ion and acidic –COOH group exits as –COO- ion, therefore overall molecule becomes neutral in nature and called as Zwitter ion. The Zwitter ion can show certain movement in their solution during electrolysis which is completely depend upon the pH of the solution.
Each amino acid shows no net movement towards any electrode at specific pH value which is called as isoelectric point. On the basis of polarity; they can be classify as polar and non-polar molecules. The polar molecule contains some functional group in the molecule apart from one amino and one carboxyl group while a non-polar molecule contains only hydrocarbon side chain. One basic amino group on alpha carbon atom can easily neutralise the effect of one acidic carboxyl group in the molecule.