12th Class Biology Molecular basis of Inheritance / विरासत का आणविक आधार Transcription

Formation of mRNA from DNA is called as Transcription. It is heterocatalytic function of DNA. Template of DNA called sense strand (Master Strand) is involved. The segment of DNA involved in transcriptions is cistron, which have a promoter region where initiation is start and terminator region where transcription ends. Enzyme involved in transcription is RNA polymerase-II. Which consist five polypeptide \[\alpha ,\beta ,{{\beta }^{'}},\omega \] (constitute core enzyme) and \[\sigma \](sigma factor). Sigma \[(\sigma )\] factor recognise promoter site while remaining core enzyme takes part in chain elongation. After transcription, DNA molecule reassociates to form its original structure. In eukaryotes hn RNA (heterogenous nuclear RNA) which consist exon (coded region) and introns (non coded region or intervening sequences) formed in nucleus and diffuse in cytoplasm is also known as split gene which goes to transcription changes for removing the introns and later formed mRNA.

It consist three phenomenon

(1) Initiation : Initiation start with help of \[\sigma \](sigma) factor of RNA polymerase enzyme. At the cap region which have 7 methyl guanosine residue at the 5^¢.

(2) Elongation : Elongation is done by core enzyme, which moves along the sense strand.

(3) Termination : In prokaryotes termination is done by rho \[(\rho )\] factor while in eukaryotes poly A tail is responsible for termination at the 3^¢.