Transcription is the process of formation of RNA from DNA.
- The structural genes are polycistronic and continuous.
- A single DNA dependent RNA polymerase catalyses the transcription of all three types of RNA that is mRNA, tRNA & rRNA
- The DNA strands unwind and one of the strands (3' → 5’) acts as the template strand.
- The RNA polymerase binds at the promoter site for transcription.
- It uses ribonucleotides for polymerization on a DNA template following complementary of bases.
- As unwinding continues, the new strand of RNA also elongates. Polymerisation occurs in the 5’ → 3’ direction.
- When RNA polymerase falls on the terminator sequence, the synthesis stops and the new RNA strand is liberated.
- The structural genes are split.
- They have exons interspread with introns. (the coding and non coding sequence respectively)
- The primary transcript of RNA undergoes splicing , by which the introns are removed and the exons are joined together.
- The hn RNA undergoes two additional processes called, capping and tailing to become mRNA.
- Methyl guanosine tri phosphate is added to the 5’ end of hn RNA in capping.
- Adenylate residues (about 200 – 300) are added at the 3’ end in tailing.
- The fully processed hn RNA is called mRNA is released from the nucleus into the cytoplasm.
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