Transcription 🧬 | Molecular Basis of Inheritance | Class 12 NCERT Biology | Genetics NEET Prep 2026” скачать в хорошем качестве

Transcription 🧬 | Molecular Basis of Inheritance | Class 12 NCERT Biology | Genetics NEET Prep 2026”

https://www.instagram.com/biologkgsir... For any contacts - contactus.biolog@gmail.com [Transcription] Transcription is the process by which the information in DNA is copied into RNA. Template: DNA Product: RNA (mRNA, tRNA, rRNA) Enzyme: RNA polymerase 1. Transcription in Prokaryotes Occurs in the cytoplasm (no nucleus). RNA Polymerase (holoenzyme) carries out transcription. It has: Core enzyme (α₂ββ′) → polymerization σ (sigma) factor → promoter recognition Steps: Initiation – Sigma factor binds promoter (–35 and –10 regions). Elongation – RNA polymerase synthesizes RNA (5′ → 3′ direction). Termination – Two types: Rho-dependent termination (needs Rho protein) Rho-independent (hairpin loop formation in RNA) mRNA produced is often polycistronic (codes for multiple proteins). Transcription and translation are coupled (occur simultaneously). 2. Transcription in Eukaryotes Occurs inside the nucleus. More complex; three different RNA polymerases: RNA Pol I → rRNA (28S, 18S, 5.8S) RNA Pol II → mRNA, some snRNA RNA Pol III → tRNA, 5S rRNA, small RNAs Promoters: TATA box, CAAT box, GC box. Requires transcription factors (TFs) for initiation (unlike prokaryotes where sigma factor alone works). Steps: Initiation – TFs + RNA Pol II bind promoter → transcription bubble. Elongation – RNA chain grows. Termination – Polyadenylation signal (AAUAAA) helps end transcription. mRNA is initially hnRNA (heterogeneous nuclear RNA) → undergoes processing: Capping (5′ cap) Splicing (removal of introns, joining of exons) Polyadenylation (Poly-A tail at 3′ end) Final product: mature mRNA (monocistronic) → exported to cytoplasm for translation. ✅ Key Differences: Prokaryotes: Single RNA polymerase, polycistronic mRNA, no RNA processing, transcription & translation coupled. Eukaryotes: Multiple RNA polymerases, monocistronic mRNA, RNA processing (capping, splicing, tailing), transcription in nucleus & translation in cytoplasm.