Transcription
The Central Dogma elucidates the process by which DNA encodes proteins, unfolding in three phases: replication, transcription, and translation. Following DNA replication of its two strands, information is transcribed into RNA.
The process of transcription in protein synthesis is as follows:
1. Transcription is the initial step in protein synthesis, where m-RNA is formed from the DNA template.
2. Initiating transcription requires the enzyme DNA-dependent RNA polymerase, copying genetic information from DNA into m-RNA.
3. A transcription unit includes a promoter, structural gene, and terminator, with the template strand in the 3’→5′ direction and the coding strand in the 5’→3′ direction.
4. Structural genes differ in eukaryotes and prokaryotes, with eukaryotic genes containing introns and exons. RNA polymerase binds to the promoter during transcription, initiating elongation.
5. Termination involves RNA polymerase and the newly synthesized m-RNA falling off when reaching the terminator region.
6. Transcription requires initiation factor (σ sigma) and termination factor (ρ rho). In eukaryotes, RNA undergoes processing with three RNA polymerase enzymes: I, II, and III.
7. RNA polymerase I forms r-RNA, II forms hn-RNA, and III forms t-RNA and sn-RNA.
8. Initially non-functional, eukaryotic RNA undergoes splicing, capping, and tailing for activation.
9. hn-RNA, after splicing, capping, and tailing, transforms into m-RNA, which leaves the nucleus in eukaryotic cells to participate in protein synthesis at ribosomes.