Nucleic acids : definition, structure and functions.

Definition : Nucleic acids are biologically occuring polynucleotides in which the nucleotide residues are linked in a specific sequence by phosphodiester bonds .Experimental studies of nucleic acids constitute a major part of modern biological and medical research, and form a foundation for genome and forensic science, as well as the biotechnology and pharmaceutical industries.

There are two types of nucleic acids namely :(1) Deoxyribonucleic acid (DNA)
                                                                  (2) Ribonucleic acid (RNA)
Brief  History :
        Nucleic acids were discovered by Friedrich Miescher in 1869, a Swiss researcher.The demonstration that DNA contain genetic information was first made in  1944,by Avery, Macleod and MacCary.

Structure : Nucleotides are building blocks of nucleic acids .This nucleotides composed by three characteristic components :(1) a nitrogenous bases (2) a pentose sugar, and (3) a phosphate group .The molecule without the phophate group is called a nucleoside .The nitrogenus bases are derivatives of two parent compounds , pyrimidin and purine.

The base of a nucleotide is joined covalently (at N-1 of pyrimidins and N-9 of purines) in an  N-β-glycosyl bond to the 1' carbon of pentose, and the phosphate is esterified to the 5' carbon .
Both DNA and RNA contain two major purine bases, adenine(A) and guanine(G) , and two major pyrimidins .In both DNA and RNA one of the pyrimidines is cytosine (C) ,but the second major pyrimidine is not the same in both: it is thymin (T) in DNA nd Uracil(U) in RNA.

The structures of five nitrogenous base, nucleotides and nucleosides are summarized below :

 Figure : General structure of nitrogenous base

Figure : Major purine (Adenine,Guanine), pyrimidine (Cytosine,Thymine,Uracil) and other components of Nucleic acids.

                                         Figure : Structure of Nucleoside

                                                Figure : Structure of Nucleotide.

The nomenclature corresponding nucleotides and nucleosides with major nitrogenous base is summarized in table :

Functions of nucleic acids :

1. DNA is the chemical basis of heredity and may be regarded as the reserve bank of genetic information.

2. DNA is exclusively responsible for identify of different species organisms over millions of years.  

3. RNA is responsible to transfer the genetic information from nucleus to cytoplasm for protein synthesis.

4. DNA  functions as the original blueprint for the synthesis of proteins.

5.  Nucleic acid are the compounds that pass hereditary information from one generation to another, making possible a remarkable continuity of life within the various species of living things. 

6.  DNA molecules are the particular type of nucleic acid out of which genes are made.
Genes are the bearers of hereditary traits from parent to off spring.

7. Nucleic acids determine the phenotype of an organism.

8.  Other functions of nucleic acids include catalysis (enzyme like action eg: ribosomes) and co enzyme action (RNA acts as co enzyme for the enzyme telomerase).