The researchers have long recognized a relationship among DNA, RNA and Protein, and this recognization have guided a vast amount of research over the past decades. The pathway from DNA to RNA and RNA to protein is conserved in all forms of life and is often called as the central dogma.
Transfer of genetic information from one generation to other occurs by replication of DNA. DNA functions as a storage molecule, holding the genetic information for the lifetime of a cellular organism, and allowing that information to be duplicated and passed to the next generation. Synthesis of duplicate DNA is directed by the parental molecule and is called replication. The process of replication is catalyzed by enzyme DNA polymerase.
The genetic information stored in the DNA is divided into units named genes. An organism to function properly and to reproduce its genetic information (genes) must be expressed at particular time and place.
Gene expression begins with the synthesis of RNA from DNA.
This process of DNA-directed RNA synthesis is called transcription because the DNA base sequence is being written into an RNA base sequence. RNA polymerase enzymes catalyze transcription.
Process of transcription yields three different types of RNA depending on the gene being transcribes. These are messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).At the last phase of gene expression, information in mRNA is decoded to polypeptide. This process is called translation. Thus the amino acid sequence of a protein is a direct reflection of the base sequence in mRNA. In turn, the mRNA nucleotide sequence is complementary to a portion of the DNA genome. In addition to mRNA, translation also requires the activities of transfer RNA (tRNA) and ribosomal RNA. Thus all three types of RNA are involved in the production of protein, based on the code present in the DNA.