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UNT BIOL 3451 - Regulation of Gene Expression in Eukaryotes
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BIOL 3451 1st Edition Lecture 22 Outline of Last 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 GenesOutline of Current Lecture I. 17.2 Programmed DNA Rearrangements Regulate Expression of a Small Number of GenesII. 17.3 Eukaryotic Gene Expression Is Influenced by Chromatin Modifications III. 17.4 Eukaryotic Transcription Initiation Is Regulated at Specific Cis-Acting Sites IV. 17.5 Eukaryotic Transcription Initiation Is Regulated by Transcription Factors That Bind toCis-Acting SitesV. 17.6 Activators and Repressors Interact with General Transcription Factors at the PromoterVI. 17.7 Gene Regulation in a Model Organism: Transcription of the GAL genes of Yeast Current LectureI. 17.2 Programmed DNA Rearrangements Regulate Expression of a Small Number of Geneso Figure 17.3- In recombination, bring 1 V region next to a J region- One of the ways to create diversityo 2 other mechanisms to increase antibody diversity- Imprecise recombination between any pair of LV and J regions; cutting in different ways will add different nucleotides to the junction where you cutThese 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.- High hypermutation (random somatic mutation) brings more variation into the LVJ region’s sequence (binds N and adds random nucleotides-4 possibilities per nucleotide: 4x4x4…)1. P nucleotides are in original DNA and found different spot2. N nucleotides are not form original (more variation)3. Somatic mutation gives you random mutations in different spotsII. 17.3 Eukaryotic Gene Expression Is Influenced by Chromatin Modificationso Most of genes on genome is not for this particular cell, usually for someone else (very small amount of genes needed for each cell)o Chromosomes are in a small part (territory) in nucleus, and are separate from other chromosomes- Transcription and translation spatially distincto Eukaryotic DNA combined with histone and non-histone proteins to form chromatin- More protein than genetic material there- Protects it there from things (like transcription factors) to prevent expression- Chromatin structure inhibits transcription, replication, and DNA repair- Usually, all the systems are designed to deal with this, unless the system breaks down, then there is a problemo In interphase, each chromosome occupies a discrete area called chromosome territoryo Channels between chromosomes called interchromosomal domainso Chromosome structure is continually being rearranged, specifically in development; done so transcriptionally active genes are cycled to the edges of chromosome territories- Transcription factories (new term): nuclear sites that contain most of the active RNA polymerase and transcription regulatory molecules (has to be in the right place)o Chromatin remodeling: important for regulating gene expression; either changesin nucleosome (histones), DNA, or other proteins; modifications might mean being moved, turned on, etc.- Most nucleosomes contain normal histones (H2A, H3)1. Are variants: H2A.Z and H3.3 that facilitate gene transcription (makes easier to turn it on)- Histone acetylation of nucleosome; catalyzed by histone acetyltransferase enzymes (HATs)1. Increases transcription (fig 17.4)a. Alteration of DNA-histone contactsb. Alteration of DNA pathc. Remodeling of nucleosome core particled. Right hand side is where more accessible- Also have phosphorylation and methylation1. Change structure, type of remodeling so causes chromatin to be more or less accessibleo Chromatin remodeling involves - Repositioning of nucleosomes (first one in fig 17.4)1. Allows for regions of chromosome accessible to transcription regulatory proteinsa. Transcription activatorsb. RNA polymerse IIc. SWI/SNF: best studied remodeling complexes- Removal of nucleosomes (last one in fig 17.4)o DNA methylation: decreased gene expression- Occurs more often on cytosine of CpG (C phosphodiester bond G- not nucleotide!) doubled in DNA- Represses transcription by binding to transcription factors of DNAIII. 17.4 Eukaryotic Transcription Initiation Is Regulated at Specific Cis-Acting Siteso Transcription regulation requires binding of many regulatory factors to specific DNA sequences- Cis-acting sequence: naturally, only affects DNA on same strand (sequence located on same chromosome as gene it is regulating)1. Promoters (where RNA polymerase is going to bind to factor; factor binds to promoters)2. Enhancers (turn up)3. Silencers (turn down)- Promoters: nucleotide sequences that serve as recognition sites for transcription machinery (transcription factors- these bind to sequence and RNA polymerase binds to factor (in humans))1. Critical for initiation of transcription2. Located adjacent to genes regulated, generally in vicinity 3. Diversity in promoters in terms of structure (sequence) and function (how they are turned on) (Fig. 17.5)a. Focused promoters: specific transcription start siteb. Dispersed promoters: several start sites, not a specific one4. Made up of one or more core elements (sequences) that bind to specific initiation proteins (always there!)a. Necessary but not sufficient (if there, it can be turned on, but it isn’t quite yet) b. Initiator (Inr), TATA box (helps to really fix starting point-notalways there), TFIIB recognition element (BRE) (for DNA polymerase II- that’s why Roman Numeral II), downstreampromoter element (DPE) (downstream means further into the gene area), motif ten element (MTE)c. Fig 17.65. Promoters primarily contain proximal promoter elements located upstream of TATA and BRE motifs, enhancing levels of basal transcriptiona. CCAAT and GC boxesb. Fig 17.7- Enhancers (cis-acting): modular and contain several short DNA sequences increasing transcription rates; complex of


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UNT BIOL 3451 - Regulation of Gene Expression in Eukaryotes

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