Operons và quá trình điều hòa hoạt động của gen

Chapter 18 - Operons Control of Gene Expression in Prokaryotes Sample Pathway for Control of Tryptophan (trp) Expression Gene 1 Gene 2 Gene 3 Gene 4 Gene 5 transcription translation Enzyme 1 Enzyme 2 Enzyme 3 Enzyme 4 Enzyme 5 Each enzyme catalyzes the next series of reactions necessary for tryptophan production Promotor (RNA polymerase binding site) DNA mRNA (transcription unit) 2 Negative Feedback shut-off systems trp Basic Vocabulary mRNA Transcription Unit: - grouping of mRNA genes with related function - 2 advantages ~ 1. organization 2. easy regulation – one “on/off” switch can be used to control an entire cluster of related genes Basic Vocabulary Operon: - an entire gene-regulating system in PROKARYOTES, which includes the operator, promotor, and all corresponding genes Basic Vocabulary Operator: - “on-off” switch to genes - controls the access of RNA polymerase to genes - found within the promotor region or between the promoter and gene-encoding regions Let’s take a closer look at the tryptophan (trp) operon…an example of a “repressor” system Overview of Repressor Trp Operon Components r. Trp Repressor Gene (always “on”) promotor rp. RNA Pol. binding site o. Operator r. rp. o. Gene 1 5 Genes needed for tryptophan production mRNA transcription unit Enz 1 Enz 2 Enz 3 Enz 4 Enz 5 Gene 1Gene 3 Gene 4 Gene 5 trp mRNA for trp repressor Trp repressor protein translated in its “inactive” form RNA polymerase Trp operon controls the production of the amino acid tryptophan How is the trp operon turned off once enough trp is made? Trp repressor gene RNA pol binding site operator Increased concentration of trp (co- repressor) increases chances of trp binding to allosteric site of inactive trp repressor Inactive trp repressor protein trp trp trp trp trp How is the trp operon turned off once enough trp is made? Active trp repressor can now bind to operator RNA polymerse, therefore is physically blocked from transcribing genes for trp Why is this a repressor system? The trp operon is a repressor operon, meaning gene expression of the operon is repressed by the presence of the co-repressor, tryptophan. Watch this animation to fully understand and review this operon, then take the on-line quiz together as a class http://bcs.whfreeman.com/thelifewire/conte nt/chp13/1302002.html [...]... lactose into glucose and galactose This is an inducible operon, meaning gene expression ß-galactosidase is stimulated by the presence of an co-inducer, lactose Inducible Lac operon promotor I Lac Inducer I mRNA for inducer protein inducer protein in “active” form crp: helps RNA pol to bind rp: RNA pol.binding site crp rp o operator Genes that promote ßgalactosidase production o RNA pol blocked from ßgalactosidase... allosteric site of induce protein, inactivating it Lac Operon Animation Watch this animation to fully understand and review the lac operon! http://highered.mcgraw-hill.com/olc/dl/12008 0/bio27.swf How are genes controlled in eukaryotes? 1) Regulation of Chromatin Structure 2) Pre and post Transcriptional Regulation 3) Pre and Post Translational Regulation Regulation of Chromatin Structure N-terminus (amino... adjacent nucleosome  loose chromatin structure results, phosphorylation is adjacent to methyl group allowing for increased transcription Pre-Transcriptional Regulation • Similar to methods used in bacterial operons, using proteins that inhibit or promote binding of RNA pol – Distal and Proximal Control Elements – Proteins involved include: • Transcription factors • Activators • Mediator Proteins Post-Transcriptional . 18 - Operons Control of Gene Expression in Prokaryotes Sample Pathway for Control of Tryptophan (trp) Expression Gene 1 Gene 2 Gene 3 Gene 4 Gene 5 transcription translation Enzyme. production mRNA transcription unit Enz 1 Enz 2 Enz 3 Enz 4 Enz 5 Gene 1Gene 3 Gene 4 Gene 5 trp mRNA for trp repressor Trp repressor protein translated