Messenger RNA is produced via the process of transcription. DNA is transcribed into mRNA using RNA polymerase. First, the double helix structure of the DNA unravels, and the hydrogen bonds break between the paired nucleotides of DNA strands by the action of DNA helicase. One strand of DNA act as a template strand or anti-sense strand to produce the complementary mRNA strand. RNA polymerase reads the DNA template strand and the RNA nucleotides are paired according complementary base-pairing rule to the DNA template strand. For example, base T pairs with A, C pairs with G, base A on DNA pairs with RNA nucleotide U (uracil).Then RNA polymerase catalyses the formation of phosphodiester bond between the ribose sugar of one RNA nucleotide to the phosphate of another nucleotide to join the individual RNA nucleotides together and form a pre-mRNA strand. The pre-mRNA is then further spliced to remove introns forming the processed mRNA consisting of exons that code for the final gene product. The processed mRNA is finally transported out of the nucleus into the cytoplasm for translation.