1-1.1 Introduction:

The main distinction between a living and non-living entity is the ability to replicate and reproduce similar offsprings. Nucleic acid molecules (DNA and RNA) present in a living organism acts as a genetic template to pass the hereditary information from one generation to the next. Nucleic acid molecules are organised as genes which code for a particular phenotype via specific proteins and the expression of a gene is regulated by both external and internal factors which aid the developmental process of an organism. This relation between genes and proteins forms the “central dogma of life”.

1-1.2 Gene :

A gene can be defined as the region of DNA (or RNA in case of virus) that controls a discrete hereditary characteristic, usually corresponding to a single protein or RNA. This includes the entire functional unit, encompassing coding (exons) and noncoding sequences (introns and regulatory sequences).

•   Exons and introns which represent the coding and noncoding regions are present in a eukaryotic gene. Introns are absent in prokaryotes.
•   The introns are removed by splicing and the exons are translated in tandem to yield the functional polypeptide that further undergoes post translational modification to become functional. These functional polypeptides (proteins) are targeted to various organelles in the cell or exported out of the cell for carrying out various intracellular and extracellular processes respectively.