Tiêu đề 24. TRANSCRIPTION AND TRANSCRIPTION FACTORS.pdf ✅

PHARMD GURU Page 1 1. INTRODUCTION: Transcription is the process by which genetic information encoded in DNA is copied into RNA. This is a critical step in gene expression and is regulated by a variety of factors to ensure precise control of cellular function. While the fundamental process of transcription is conserved across prokaryotic and eukaryotic organisms, the complexity and regulation differ significantly. 2. BASIC PRINCIPLES OF TRANSCRIPTION IN PROKARYOTES: A. OVERVIEW: Transcription in prokaryotes is relatively simple due to the absence of a defined nucleus and the streamlined nature of their genetic material. The process involves the synthesis of RNA from a DNA template, mediated by RNA polymerase. B. STAGES OF TRANSCRIPTION IN PROKARYOTES: a) INITIATION:  Promoter Recognition: RNA polymerase binds to a specific DNA sequence called the promoter, which contains conserved sequences at the -10 (TATAAT, Pribnow box) and -35 (TTGACA) regions relative to the transcription start site.  Role of Sigma Factor (σ): The core RNA polymerase enzyme requires the sigma factor to recognize and bind to promoter sequences. The sigma factor dissociates after initiation.  Open Complex Formation: Once bound, the DNA strands unwind, forming an open complex, exposing the template strand for RNA synthesis. b) ELONGATION:  RNA Synthesis: RNA polymerase adds ribonucleotides complementary to the DNA template strand in the 5’ to 3’ direction.  Unwinding and Rewinding: DNA unwinds ahead of RNA polymerase and rewinds behind it. TRANSCRIPTION AND TRANSCRIPTION FACTORS

PHARMD GURU Page 3 Figure 1: Diagram illustrating the structure of RNA polymerase and its interaction B. STAGES OF TRANSCRIPTION IN EUKARYOTES: a) INITIATION:  RNA Polymerases:  RNA Polymerase I: Transcribes rRNA (except 5S rRNA).  RNA Polymerase II: Transcribes mRNA and small nuclear RNAs (snRNAs).  RNA Polymerase III: Transcribes tRNA, 5S rRNA, and other small RNAs.  Promoter Elements:  TATA Box: Located ~25-30 bp upstream of the transcription start site, recruits TATA-binding protein (TBP).  Initiator (Inr) Sequence: Surrounds the transcription start site, essential for transcription initiation.  Proximal Promoter Elements (CAAT box, GC box): Help regulate transcription efficiency.  Pre-Initiation Complex (PIC): A multi-protein complex involving TFIID, TFIIA, TFIIB, TFIIE, TFIIF, and TFIIH, which stabilizes RNA polymerase II at the promoter.