Nucleic acids are water soluble high molecular weight polymers with about 9% phosphorous and are found in high concentration in cell nuclei. Almost a century of experimentation is spent to know the basic principles of nucleic acid and structure.
Nucleic acids have been unequivocally identified as the species responsible for the control of genetic processes and are thus central to the control of reproduction.
Nucleic acids are of two kinds-
i) deoxyribonucleic acid (DNA)
ii) ribonucleic acid (RNA)
There are many kinds of each of DNAs and RNAs.
It appears that any living cell contains only one or very few very large DNA molecules and at present, the determination of complete covalent structure of DNA molecules seems very difficult because of their large size; for example an E. Coil cell contains a single DNA molecule of molecular weight about 2×10^9. At least three distinct types of RNA have been recognised in all living cell. These are-
1. Transfer RNA (tRNA), which is dissolved in the cytoplasm and makes about 15% of the total RNA of most cells.
2. Ribosomal RNA (rRNA), which occurs in cytoplasmic particles called ribosome and makes about 80% of the total RNA.
3. Messenger RNA (mRNA), which is the least clearly characterised and occurs in small quantities.
Transfer RNA has molecular weight about 2500 and a few have been isolated in their pure form and their covalent structures have been established. However messenger RNAs and the main component of ribosomal RNA have very high molecular weights (around 500000); thus the possibility of their structure elucidation seems remote.
(Source: Dr. Sujit Ranjan Acharjee, Associate professor of Chemistry, Department of Chemistry, Hojai College, Hojai)