HOW DO CELLS KNOW WHEN TO EXPRESS A GENE? DO NOW:

DO YOU USE ALL YOUR GENES? ALL THE TIME? Consider…

Gene Expression You have the genes…now what? DNA vs. RNA

2 Processes Involved in Gene Expression Transcription Translation Both involve 3 basic steps: Initiation Elongation Termination

3 billion base pairs: Where’s the Gene?? Promoter id’s gene 2 common conserved sequences in eukaryotes: TATA box ~ 25 bp upstream (TATAAA) CAAT ~ 100 bp

What identifies the promoter? Transcription factors Basal tf – minimal level of transcription RNA Polymerase Together form Initiation Complex

Other Factors: Enhancers Further away from gene (1000s bp) Activator proteins may bind

Initiation When both complex and activator proteins in place, transcription begin BOTH PROMOTER AND ENHANCER REQUIRED FOR PROPER GENE TRANSCRIPTION Additional tf = higher levels of transcription

Elongation & Termination RNA Polymerase Build RNA in 5’  3’ What direction is DNA read? Terminator Sequence In eukaryotes, not clearly defined

EUKARYOTIC CELLS PRODUCE PRE-MRNA FROM TRANSCRIPTION

Post-Transcription processing in Eukaryotes 5’ cap Methylated Guanine 5’ – 5’ phosphodiester bond Recognition by proteins involved in translation Poly A tail added to 3’ end Prevents degradation in cytoplasm

Post-transcription modification Pre-mRNA composed of both introns & exons Removal of introns by spliceosomes Modifying pre-mRNA

mRNA made by transcription… Non-coding leader sequence at 5’ end Recognition sites to bind to ribosome Start codon – AUG Coding sequence Stop codon – UAA, UGA, UAG Non-coding trailing sequence at 3’ end

Sources: ng/genetics/transcr3.htm ng/genetics/transcr3.htm hp#process hp#process