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Download Protein Synthesis - Quinnipiac University
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Regulation of Gene Expression In Prokaryotes Regulation of Gene Expression • Constituitive Gene Expression (promoters) • Regulating Metabolism (promoters and operators) • Regulating Development (sigma switches) Constituitive Gene Expression (promoters) promoter coding sequence Regulating Metabolism (promoters and operators) promoter operator coding sequence Major and minor grooves - protein binding Major and minor grooves - protein binding Recognition involves the major groove Regulatory Proteins Bind DNA negative control positive control Many regulatory proteins are dimers and bind to palindromes Repressors & metabolic pathways repressor deactivated genes ON product repressor activated genes OFF energy Synthetic Pathway precursor molecules energy macromolecule Degredative Pathway repressor activated genes OFF substrate repressor deactivated genes ON Metabolic signals and repressor activity metabolic signal molecule gene off gene on gene on gene off repressor protein DNA binding site the lac operon Lactose Metabolism the metabolic signal for repression Negative Control When activated by binding of the metabolic signal molecule, the lac repressor binds to the operator, blocking RNA polymerase Negative control in the lac operon the lac operon Conventional interpretation of dominance focusing on enzyme function QuickTime™ and a Animation decompressor are needed to see this picture. Conventional interpretation of codominance focusing on enzyme function QuickTime™ and a Animation decompressor are needed to see this picture. But alternatively, control regions can be involved - a recessive operator mutation But alternatively, control regions can be involved - a dominant operator mutation But alternatively, control regions can be involved - one inducer mutation But alternatively, control regions can be involved - another inducer mutation the Lac control region Cyclic AMP Positive Control cAMP is present when glucose is unavailable cAMP binds to CAP protein, which then binds to the promoter binding of the CAP-cAMP complex to the promoter, activates it CAP-cAMP positioning of CTD CAP-cAMP acts in formation of closed promoter The Lactose Operon: Control of a degredative pathway Practice Answers Trp operon, control of a a biosynthetic pathway The Tryptophan Operon: Control of a synthetic pathway Tryptophan Synthesis allosteric protein Attenuation of trp The leader sequence: two trp codons and a stop codon The mechanism of attenuation - termination Region 2 can bind with 1 or 3, but affinity for 1 is higher Over riding attentuation if shortage of trp causes ribosome to stall, 2 binds with 3 …no terminator hairpin forms Control of development: Sigma switching Different sigmas and their regions of homology RNA polymerase in bacteria core enzyme RNA polymerase sigma Sigma factors recognize promoters and disassociate when the RNA polymerase binds to the promoter, leaving the core enzyme to make the transcript Phage SPOI (in B. subtilis) • 3 phases of gene expression – Early phase – Mid phase – Late phase • Each phase uses a different sigma, each recognizing a different promoter • The genes of each phase all have the same kind of promoter, recognized by one of the sigma factors Sigma Switching • Early phase. Early genes have promoters recognized by the host’s RNA polymerase. gp28 is an early protein that acts as a sigma factor for the middle phase genes. gp28 has a higher affinity for the CORE’s binding site than it’s own sigma, thus displacing the host’s sigma and turning off the early genes and turning on the mid genes. early transcripts early proteins, including gp28 middle transcripts middle proteins, including gp33, gp34 late transcripts late proteins hostphase genes have promoters recognized by gp28. Gp33 and gp34 are Middle middle proteins that actsigma as a sigma factor for the late genes. • Middle phase . • Late phase gp28 sigma gp33-34 sigma Lambda Lysogenic Life Cycles - Temperate Viruses Genetic map of Lambda 3 phases again N antitermination Q antitermination cI and cro duke it out Establishing Lysogeny Maintaining Lysogeny Induction SOS Prokaryote versus Eukaryote Comparison Prokaryotes Eukaryotes Transcription Factor (eukaryotic sigma) sigma Step 1 promoter Step 1 promoter promoter Step 2 Step 2 Positive control in eukaryotes - gene enhancers Gene activation in Eukaryotes: A different complicated initiation complex for each different context in which a gene is expressed
