DNA
In most living organisms (except viruses), the genetic information is stored in the molecule called deoxyribonucleic acid or DNA. DNA is made and it resides in the nucleus of the living cells. The name DNA was derived from the sugar molecule contained in its backbone—deoxyribose. The high molecular weight nucleic acid, DNA, is found chiefly in the nuclei of complex cells, known as eukaryotic cells, or in the nucleoid regions of prokaryotic cells, such as bacteria.
The first isolation of DNA was accomplished by Johann Friedrich Miescher in 1870. He reported a weakly acidic substance of unknown function and named it as nuclein. A few years later, Miescher separated nuclein into protein and nucleic acid components. In the 1920s, nucleic acids were found to be major components of chromosomes. Nucleic acids contain C, H, N, O and P. Unlike proteins, nucleic acids contain no sulphur. Nucleic acids are acidic in nature due to the phosphoric acid moiety.
RNA
‘RNA’ is distributed throughout the cell, most commonly in small numerous organelles called ‘ribosomes’. It is a lower molecular weight, but much more abundant nucleic acid. The RNAs play a vital role in the transfer of genetic information (transcription) from the DNA library to the protein factories called ribosomes, and in the interpretation of that information (translation) for the synthesis of specific polypeptides. These functions are described in later chapters. Some RNAs, called ‘ribozymes’, have catalytic activity.