BIOL 3451 1st Edition Lecture 21 Outline of Last Lecture I. 15.5 Organisms Use DNA Repair Systems to Counteract MutationsII. 15.6 The Ames Test Is Used to Assess the Mutagenicity of CompoundsIII. 15.7 Geneticists Use Mutations to Identify Genes and Study Gene FunctionIV. 15.8 Transposable Elements Move within the Genome and May Create Mutations V. 16.1 Prokaryotes Regulate Gene Expression in Response to Environmental ConditionsVI. 16.2 Lactose Metabolism in E. coli Is Regulated by an Inducible SystemVII. 16.3 The Catabolite-Activating Protein (CAP) Exerts Positive Control over the lac OperonOutline of Current Lecture I. 16.3 The Catabolite-Activating Protein (CAP) Exerts Positive Control over the lac OperonII. 16.4 Crystal Structure Analysis of Repressor Complexes Has Confirmed the Operon ModelIII. 16.5 The Tryptophan (trp) Operon in E. coli Is a Repressible Gene SystemIV. 16.6 Attenuation Is a Process Critical to the Regulation of the trp Operon in E. coliV. 16.7 Riboswitches Utilize Metabolite-Sensing RNAs to Regulate Gene ExpressionVI. 16.8 The ara Operon Is Controlled by a Regulator Protein That Exerts Both Positive and Negative ControlVII. 17.1 Eukaryotic Gene Regulation Can Occur at Any of the Steps Leading from DNA to Protein ProductVIII. 17.2 Programmed DNA Rearrangements Regulate Expression of a Small Number of Genes Current LectureI. 16.3 The Catabolite-Activating Protein (CAP) Exerts Positive Control over lac Operono Can live off of lactose in absence of glucose , CAP exerts positive control by binding to the CAP-binding site, facilitating RNA polymerase binding at the promoter and transcriptioni. CAP is volume control and repressor is on/offii. Figure 16.8o For CAP to bind to promoter efficiently, must be bound to cyclic adenosine monophosphate (cAMP)i. Glucose inhibits activity of adenylyl cyclase which makes ATP and prevents cAMP from being produced and doesn’t allow for bindingii. Fig 16.8 and 16.9These 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. 16.4 Crystal Structure Analysis of Repressor Complexes Has Confirmed the Operon Modelo Three sites for repressor binding with lac operoni. Fig. 16.10ii. All three must be bound for maximum repressioniii. Repressors bind to O1 and O3 (operators), which creates repression loop (prevents access of RNA polymerase to the promoter)1. Fig 16.11 III. 16.5 The Tryptophan (trp) Operon in E. coli is a Repressible Gene Systemo 5 enzymes needed for trp production, and they are part of operon i. Fig. 16.12o In presence of tryptophan, operon repressed, and no enzymes producedi. Tryptophan is corepressor, and when present, shuts system down o When absent, called acorepressoro Trp structural genes are preceded by leader sequence containing regulatory site called an attenuatorIV. 16.6 Attenuation Is a Process Critical to the Regulation of the trp Operon in E. colio Attenuation: transcription of leader region of the trp operon can occur even when the operon is repressed in the presence of tryptophani. in absence, transcription isn’t terminated in leader region, and continues through entire operonii. The attenuation mechanism is common to several operons for enzymes responsible for synthesis of other amino acids1. Includes threonine, histidine, leucine, and phenylalanineo Leader regions form two different conformations i. Palindrome sequences: can be read either way and means the same thingii. Hairpin structures (conformations) form in presence and absence of tryptophan 1. Terminator: presence, called transcriptional terminator; does this because the ribosome is able to proceed through the sequence2. Antiterminator: absence, transcription proceeds (RNA polymerasegets to move on); does this because ribosome stalls at these codons because there is not adequate charged tRNAtrp3. Figure 16.13 *Know this*iii. Leader region: has two tryptophan codonsiv. LOOK AT (2 slides)o TRAP (trp RNA-binding attenuation protein): protein required in attenuation (used in Bacillus subtilis- used instead of ribosome stalling)i. has 11 subunits, each can bind one molecule of tryptophanii. fully saturated TRAP can bind to 5’ leader sequence, form terminator hairpin, then prevent antiterminator hairpin (Fig. 16.14) iii. Traps in specific shape to allow terminator hairpin structure to form.iv. Also have anti-TRAP (AT): gene that is induced by expression of uncharged tRNA1. Make AT protein in tryptophan-activated state and inhibits bindingto target leader RNA sequenceV. 16.7 Riboswitches Utilize Metabolite-Sensing RNAs to Regulate Gene Expressiono Many cases of gene regulation need forms of mRNA, involve riboswitchesi. Riboswitches: Present upstream from coding sequence and prevent/ regulate downstream1. Possess metabolite-sensing RNA sequence that allows transcription of that RNA to either proceed or not proceed2. Binds small molecule called aptamer (binds to ligand) and expression platform (capable of forming terminator structure)3. No regulators can avoid RNA, but they can DNA and protein4. Fig. 16.15VI. 16.8 The ara Operon is controlled by a Regulator Protein That Exerts Both Positive and Negative Controlo Arabinose (ara) operon: subject to both positive and negative regulation by AraCproteini. Metabolism governed by enzymatic products of structural genes ara B, A,and Do Transcription contolled by regulatory protein AraC, which interacts with two regulatory regions: aral and araO2i. AraC binds to aral with arabinose present and CAP-cAMP= induce expressionii. Absence of arabinose and CAP-cAMP: AraC binds to both aral and araO2 to form loop that causes repressioniii. Fig. 16.15VII. 17.1 Eukaryotic Gene Regulation Can Occur at Any of the Steps Leading from DNA to Protein Producto Make RNA, Process it, export out of nucleus, and regulation can occur at any of these steps= complexityo Complex because….i. Larger amounts of DNA that are associated with histones and other proteinsii. mRNAs have to be spliced, capped, and polyadenylated before transport from nucleusiii. chromosome in double membrane nucleus (has to be exported)iv. movement of RNAs into cytoplasm after transcription (RNA targeting: saysto go to the right place)v. RNA stability (half-life in prokaryotes is only 2-3 minutes; but in eukaryotes, we make RNA, repress it, and then have an inducer ready if need the RNA really quickly)vi. Modulation of mRNA translation as well as protein