GCD 3022 1st Edition Lecture 20 Outline of Last Lecture I Transcription a Rho independent and rho dependent b Sigma factor i Mutation ii Transcription initiation and role of sigma factor c Transcription region d Coding and template strands II Translation a Gene mapping b Splicing i Mutation ii Introns and exons iii Coding information in eukaryotes c Translated RNAs i Type of translated RNA ii tRNA anticodon d Mistakes in translation i Anti codon mutation These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute ii Start and stop codons e Termination of translation i Site of termination ii Number of codons translated f Prokaryotic vs Eukaryotic initiation g A P and E sites III Consensus sequence IV Degenerate genetic code Outline of Current Lecture I Introduction a Gene regulation b Unregulated genes c Benefit of regulating genes II Overview of transcriptional regulation a Timing of regulation in bacteria b Regulatory proteins i Repressors ii Activators c Negative and positive control d Effector molecules i Inducers ii Corepressors iii Inhibitors III Regulation of the lac operon a Operon b Transcriptional units i lac operon 1 DNA elements 2 Structural genes ii lacI gene c Regulation by a repressor protein i Transcriptional regulation ii Inducible negative control d lacI gene experiment i problem ii set up iii hypothesis iv conclusion Current Lecture I Introduction a Gene regulation the level of gene expression that varies under different conditions b Unregulated genes also called constitutive These genes have constant levels of expression and often encode proteins that are continuously necessary for the organism s survival c Benefit of regulating genes ensures that proteins are produces only when required by the cell This process aids in metabolism response to environmental stress and cell division Regulation can occur at any of the points along the way to gene expression II Overview of transcriptional regulation a Timing of regulation in bacteria the most common way to regulate gene expression in bacteria is by influencing the initiation of transcription rate of RNA synthesis b Regulatory proteins i Repressors bind to DNA and inhibit transcription ii Activators bind to DNA and increase transcription rate c Negative and positive control negative control means that transcription is regulated by repressors and positive control means that transcription is regulated by activator proteins d Effector molecules bind to regulatory proteins not directly to DNA i Inducers bind to activators and cause them to bind to DNA or bind to repressors and prevent them from binding to DNA ii Corepressors bind to repressors and cause them to bind to DNA iii Inhibitors bind to activators and prevent them from binding to DNA III Regulation of the lac operon a Enzyme adaptation when a particular enzyme appears in the cell only after the cell has been exposed to the enzyme s substrate b Operon regulatory unit consisting of a few structural genes under the control of one promoter Encodes a polycistronic mRNA contains the coding sequence for two or more structural genes Contains promoter terminator structural genes and operator c Transcriptional units i lac operon 1 DNA elements promoter binds DNA polymerase operator binds lac repressor protein and CAP site binds catabolite activator protein CAP 2 Structural genes a lacZ encodes B galactosidase enzymatically cleaves lactose and lactose analogues and converts lactose to allolactose isomer b lacY encodes lactose permease membrane protein required for transport of lactose and analogues c lacA encodes galactoside transacetylase covalently modifies lactose and analogues ii lacI gene not considered part of the lac operon Has its own promoter i promoter Constitutively expressed at very low levels and encodes the lac repressor only a small amount of this protein is needed to repress the lac operon d Regulation by a repressor protein i Transcriptional regulation lac operon can be regulated by a repressor protein or by an activator protein ii Inducible negative control more frequent way of regulation Involves the lac repressor protein and allolactose as the inducer binds to lac repressor and inactivates it Repressor does not completely inhibit transcription e lacI gene experiment Jacob Monod and Pardee identified a few rare mutant strains of bacteria with an abnormal lactose adaptation One type involved a defect in the lacI gene in which the lac operon was constitutively expressed even in the absence of lactose These mutations mapped very close to the lac operon i Problem to determine the mode of regulation of the lac operon ii Set up identified plasmids F factors that carried portions of the lac operon These are also called merozygotes or partial diploids because they have one copy of the lacI gene on the chromosome and the other on the F factor This separation of the lacI gene meant that the gene on the F factor is not physically connected to those on the bacterial chromosome iii Hypothesis either the inducer protein produced from the chromosome can diffuse and activate the lac operon on the F factor or the repressor from the F factor can diffuse and turn off the lac operon on the bacterial chromosome iv Conclusion the mechanism is a trans acting mutation which means that genetic regulation can occur even though DNA segments are not physically adjacent This is mediated by genes that encode regulatory proteins