GCD 3022 1st Edition Lecture 20Outline of Last Lecture I. Transcriptiona. Rho independent and rho dependentb. Sigma factori. Mutationii. Transcription initiation and role of sigma factorc. Transcription regiond. Coding and template strandsII. Translationa. Gene mappingb. Splicingi. Mutationii. Introns and exonsiii. Coding information in eukaryotesc. Translated RNAsi. Type of translated RNAii. tRNA anticodond. Mistakes in translationi. Anti-codon mutationThese 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 codonse. Termination of translationi. Site of terminationii. Number of codons translatedf. Prokaryotic vs. Eukaryotic initiationg. A, P, and E sites III. Consensus sequenceIV. Degenerate genetic codeOutline of Current LectureI. Introductiona. Gene regulationb. Unregulated genesc. Benefit of regulating genesII. Overview of transcriptional regulationa. Timing of regulation in bacteriab. Regulatory proteinsi. Repressors ii. Activators c. Negative and positive controld. Effector moleculesi. Inducersii. Corepressorsiii. InhibitorsIII. Regulation of the lac operona. Operonb. Transcriptional units i. lac operon1. DNA elements2. Structural genesii. lacI genec. Regulation by a repressor proteini. Transcriptional regulationii. Inducible, negative controld. lacI gene experimenti. problemii. set up iii. hypothesisiv. conclusionCurrent LectureI. Introductiona. 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 regulationa. 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 proteinsi. Repressors: bind to DNA and inhibit transcriptionii. Activators: bind to DNA and increase transcription ratec. Negative and positive control: negative control means that transcription is regulated by repressors and positive control means that transcription is regulatedby activator proteins.d. Effector molecules: bind to regulatory proteins, not directly to DNAi. 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 DNAiii. Inhibitors: bind to activators and prevent them from binding to DNAIII. Regulation of the lac operona. 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 unitsi. lac operon1. DNA elements: promoter (binds DNA polymerase), operator (bindslac 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 thelac operon).d. Regulation by a repressor proteini. 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 thelac repressor protein and allolactose as the inducer (binds to lac repressorand 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 operonii. 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 onthe 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