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Download 17.2 Changes in Chromatin Structure Affect the Expression of Genes
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17.1 Eukaryotic Cells and Bacteria Have Many Features of Gene Regulation in Common, but They Differ in Several Important Ways • Each structural gene has its own promoter, and is transcribed separately. • DNA must unwind from the histone proteins before transcription. • Activators are more common in Eukaryotes. • Transcription and translation are separated in time and space. 17.2 Changes in Chromatin Structure Affect the Expression of Genes • DNase I hypersensitivity • DNase I hypersensitive sites: more open chromatin configuration site, upstream of the transcription start site • Histone modification • Addition of methyl groups to the histone protein tails • Addition of acetyl groups to histone proteins 17.2 Changes in Chromatin Structure Affect the Expression of Genes • Chromatin remodeling • Chromatin-remodeling complexes: bind directly to DNA sites and reposition nucleosomes • DNA methylation of cytosine bases adjacent to guanine nucleotides (CpG)–CpG islands 17.3 The Initiation of Transcription Is Regulated by Transcription Factors and Transcriptional Activator Proteins • Trancriptional activators, coactivators, and repressors 17.3 The Initiation of Transcription Is Regulated by Transcription Factors and Transcriptional Activator Proteins • Transcriptional activator protein GAL4 Concept Check 1 Most transcriptional activator proteins affect transcription by interacting with . a. b. c. d. introns the basal transcription apparatus DNA polymerase nucleosomes Concept Check 1 Most transcriptional activator proteins affect transcription by interacting with . a. b. c. d. introns the basal transcription apparatus DNA polymerase nucleosomes 17.3 The Initiation of Transcription Is Regulated by Transcription Factors and Transcriptional Activator Proteins • Enhancers and insulators • Enhancer: DNA sequence stimulating transcription from a distance away from promoter • May increase transcription of many genes in vicinity • Insulator: DNA sequence that blocks or insulates the effect of enhancers 17.3 The Initiation of Transcription Is Regulated by Transcription Factors and Transcriptional Activator Proteins • Coordinated gene regulation • Response elements: common regulatory elements upstream of the start sites of a collective group of genes in response to a common environmental stimulus • Heat-shock proteins 17.4 Some Genes Are Regulated by RNA Processing and Degradation • Gene regulation through RNA splicing 17.4 Some Genes Are Regulated by RNA Processing and Degradation • The degradation of RNA • 5′-cap removal • Shortening of the poly(A) tail • Degradation of 5′ UTR, coding sequence, and 3′ UTR 17.5 RNA Interference Is an Important Mechanism of Gene Regulation • Small interfering RNAs and microRNAs • RISC: RNA-induced silencing complex 17.5 RNA Interference Is an Important Mechanism of Gene Regulation • Mechanisms of Gene regulation by RNA interference • RNA cleavage: RISC containing an siRNA, pair with mRNA molecules and cleavage to the mRNA • Inhibition of translation • Transcriptional silencing: altering chromatin structure • Silencer-independent degradation of mRNA 17.6. Some Genes Are Regulated by Processes That Affect Translation or by Modification of Proteins • Model Genetic Organism • The plant Arabidopsis thaliana
