Ribose Nucleic Acid:




Ribose nucleic acids, when researchers’ realized that life originated on this planet as RNA world nearly 3.8 billion years ago. It is now considered as primeval molecule of life, and the life originated with RNA as the genetic material. Once DNA was deemed as the sole genetic materials of all living organisms, till the discovery of Tobacco Mosaic Virus (TMV) (Russian scientist), which contained RNA, now RNA can act as the genetic material.  Once RNA was considered as an accessory form of nucleic acids sub-serving, but soon people realized, that some RNAs have coded information and some were capable of performing catalytic activity, where proteins were once considered as the sole macromolecules capable performing enzymatic catalytic functions.  When life originated around 3.1-3.2 billion years ago, it was the RNA world. Everyone now trying to understand, how RNA world gave rise to DNA world. DNA world as genetic material is dominant, yet RNA has a hold on DNA’s function.  Ever since Feulgan demonstrated, by chromogenic reactive agents, that there are two types of nucleic acids, one Feulgan positive called DNA and the other Feulgan’s negative called RNA, understanding of the chemistry, structure and functions in detail has been the goal of a large number of molecular biologists, yet there are many aspects of RNA remain shrouded with mystery.


Quantity of RNA in a cell:


More than 90% of the total RNA of the cell is found in cytoplasm, the rest of it is in the nucleus especially in nucleolus region. 

Active cells contain more RNA than inactive or resting cells. Perhaps highest concentration RNA is found in brain cells, as they are the most active cells in human body. 

Shorter half-life of some types of RNAs is of importance to cellular development and stability.




Chemical analysis of RNA shows greater similarities with DNA with respect to the components it contains.  It is basically made-up of a ribose sugar (where as DNA contains deoxyribose sugar), a phosphate group (DNA also contain the similar phosphate groups), and nitrogenous bases such as adenine, guanine, cytosine (all the three are also present in DNA) and uracil (DNA contains Thymidine in the place of Uracil).




Composition of Nucleotides in RNA varies from one species to the other, and depends on what template on which it is formed and at what time.





All RNAs, whatever may be the type, structure and functions they perform exist as polynucleotide chains with 5’ to 3’ polarity.




Size and molecular weight of RNAs molecules vary from one species to the other, which range from 20-22 ntds (60x365= 21900 Daltons) to 10 000 or more (365 0000 Daltons).



Even higher order of organization is possible with association of more than one RNA chains and a variety of proteins into a complex and compact 3-D structure ex. RNA+RNPs-Ribosomes.


Based on structural organization and functions, RNAs have been classified, into Ribosomal RNA (rRNA more than 90% of cellular RNA), Transfer RNA (tRNA) and Messenger RNA (mRNA). These are the major class of RNAs involved in decoding the information into polypeptides.  But there is another category of small Mol.wt RNAs called non coding RNAs (ncRNAs).  Recent estimation of them is approximately 10, 000 or more. They are now named as ncRNAs most of them are functional RNAs ex.  Sc RNA, Sn RNA, Antisense RNAs such as Si RNAs or Mi micro RNAs, Primer PriRNAs, GuideG  RNAs, Efference eRNAs,  Xist RNAs, piRNAs, pRNAs (p1RNase), Tm RNAs (transfer-mRNA like), SnoRNAs, , Telomeric RNA, 7sRNA, 7sK RNA, B2 RNA, Srp RNA,  and many more (Refer to the chapter ‘small molecular wt. RNAs’).  According to ENCODE information the HUGO people have given ~3000 specific names for the small ncRNAs. With the exception of mRNA, tRNA and Genetic RNAs all others can be clubbed into Non Coding RNAs (Nc small RNAs). Most of these ncRNA are transcribed by non-coding DNA and many of them derived from regular transcripts but most of them are regulatory in nature.