BIO 3170 Lecture Notes - Lecture 8: Stem-Loop, Transfer Rna, Tryptophan
25 Feb 2017
School
Department
Course
Professor
Control of Gene expression Prokaryotes
• NEW SLIDE 17
The Tryptophan (trp) operon
• Binding of repressor is regulated by a ligand tryptophan
• Binding increases the affinity for the receptor which eventually precents RNA polymerase from
binding
• * Do’t reeer the struutures
• 3 enzymes ooing from 5 epeptides and the 5 peptides are encoded by 5 genes
Regulator region of TRP
• 1 regulatory site for 5 genes
• Attenuation – allows for RNA polymerase (begins after the opertartor) TSS SITE to get into the
strucutural genes, there is a stop gene??
Two major types of transcriptional control
• COMPARING LACTOSE (allolactose regulation)
o Binding of alloclatos te receptor loses the affinity for the site
o Negative and positive regulation mediated by the CAP protein
o Cylci amp increases the affinity of ligand to CAP sites
• COMPARING TRP
o Binding increases affinity for operator site
o There is no positive regulation
o Instead there is attenuation
Yellow boxes ( -10 box and -35 box)
• Attenuator allows for transcription to be turned off prior to reaching strucutural genes
o RNA polymerase initiates transcription at the ebeiing of leader sequence→ transciptens
attenuator sequence → terminator sequence
o Intrinsic terminator for RNA polymerase – strucutural formation of the hairpin loop by
the RNA
▪ Allws for the dissociation of the RNA from the DNA template
▪ Hairpin loop – strucuure that allows for RNa polymerase to come off and not
transcribe into the structural genes.
• ATTENUATION is not psobiel in a eukaryoteic cell because transcription and translation occur in
different places in eukaryotes therefore they cannot be coupled
Two Mechanisms
• TRansciption starts @ begiingin of leader
• Transcrpt is divided into four regions
o LEADER RNA → translation→ LEADER PEPTIDE
find more resources at oneclass.com
find more resources at oneclass.com
