Nucleic acids are macromolecules composed of many (polymers) small sub-units called nucleotides. There are two types of nucleic acids i.e. DNA (deoxyribonucleic Acid) and RNA (Ribo nucleic Acid). They are the chemical constituents of the chromosomes. These nucleic acids were first discovered by a Swiss biochemist Friedrich Meischer in 1871.
Each nucleotide consists of phosphoric acid (phosphate), a five carbon sugar and a nitrogenous base. Nucleotide= Phosphoric acid + sugar + nitrogenous base. The sugar and the base combination without phosphoric acid is called nucleoside. Phosphoric acid + nitrogenous base= neucleoside. Phosphoric acid + nitrogenous base= nucleoside. Different components of nucleic acids are briefly discussed below.
(i) Phosphoric acid- The acidic nature of the nucleic acid is due to the presence of phosphoric acid. Sugar of the nucleoside combines with phosphoric acid by a phosphoester bond.
(ii) Sugar- it is five carbon (pentose) sugars. There are two types of sugars i.e. ribose and deoxyribose sugars. RNA shows ribose sugar and DNA shows deoxyribose sugar.
(iii) Nitrogenous base- Each nucleic acid has four nitrogenous bases, two purines and two pyramidines. The purines are adenine and guanine and pyramidines are thymine and cytosine. In case of RNA, uracil (pyramidine) is present in place of thymine.
The DNA is double stranded helix made of many neucleotides. The two strands (poly neucleotide chains) run parallel to each other like a stair case. DNA controls all the cellular activities for which the necessary informations are coded there.
RNA- the RNA present in all living cells. Three types of RNA: mRNA, tRNA, rRNA are found. RNA is generally single straneded and is made of a chain of polynucleotides. mRNA is a transcribed from the DNA and carries all informations from nucleus to cytoplasm where by help of tRNA and rRNA they synthesize proteins for different functions.