Chapter 18 Gene Expression Eukaryotes How do eukaryotes regulate which genes are expressed in what amounts and when Learning goals By the end of this class you should be able to 1 Describe how DNA winding regulates gene expression 2 Describe how transcription factors can either positively regulate gene expression 3 Comprehend how one gene can result in multiple different protein products 4 Predict how phosphorylation can active a protein 5 Comprehend the difference in gene regulation in Prokaryotes and Eukaryotes Mechanisms of Gene Regulation Eukaryotes Nucleus Cytoplasm Chromatin Remodeling DNA wraps almost 2 times around a group of 8 and a histone called H1 seals it The are packed into 30 nm fibers then attached to scaffold proteins which can be highly condensed during cell division Must chromatin be relaxed for RNA polymerase to bind to a promoter Two pieces of evidence support this hypothesis Found DNase would find and cut up only those genes in cells which were actively expressed Must chromatin be relaxed for RNA polymerase to bind to a promoter Two pieces of evidence support this hypothesis Second mutants that do not produce normal histones produces high transcription of genes that are normally never transcribed How is chromatin altered Chromatin Remodeling Some work has shown that modifications of histones play an important role Acetylation of histones by histone acetyl HATs is usually associated with positive control Histone deacetylases HDACs remove acetyl groups causing it to condense Initiating Transcription Most promoters like the conserved TATA box sequence are bound by TATA binding TBPs Many genes also have promoter proximal elements that are unique to specific genes unlike the promoter region TATA Box TATA Binding Protein TATA Binding Proteins The binding of the TATA binding proteins tell the cell What to transcribe our DNA in Where to transcription Protein binding at both places Differential genes expression Eukaryotic genes are turned when specific regulatory proteins bind to enhancers and promoter Proximal elements and genes are turned off when regulatory proteins bind to or when chromatin remains EP SP Enhancer Silencers RP X Regulatory transcription factors proteins that bind to or promoter proximal elements Responsible for the expression silencing of particular genes in certain cell types Basal transcription factors interact with the promoter and are not restricted to particular cell types Don t do much in the way of Are transcription factors always a positive regulatory of transcription Does every transcription factors always activate transcription Mechanisms of Gene Regulation Eukaryotes Post Transcriptional Control 1 mRNA in various ways 2 Modifying the span of mRNAs 3 Activating or inactivating proteins after translation has occurred 1 Alternative Splicing of mRNAs During splicing changes in gene expression are possible because select may be removed from the primary transcript along with introns As a result the same primary DNA sequence can yield more than one kind of mature consisting of different combinations of exons 2 mRNA Stability and RNA Interference 1 RNA polymerase transcribes small RNA 2 MicroRNA miRNA is formed by initial processing 3 Hairpin loop is to form mature miRNA 4 Taken up by RNA induced silencing complex RISC Now called small interfering mRNA siRNA 5 miRNA binds to target mRNA 6 If the match is an enzyme inside RISC cuts mRNA 3 Post Translational Control Proteins are into their final conformation by chaperone proteins allowing them to function properly 3 Post Translational Control Proteins are folded into their final conformation by chaperone proteins allowing them to function properly Phosphorylation is a very common mechanism for or proteins 3 Post Translational Control Proteins are folded into their final conformation by chaperone proteins allowing them to function Phosphorylation is a very common mechanism for activating or deactivating proteins Ubiquination targets proteins for by the proteasome Comparing Gene Regulation in Prokaryotes and Eukaryotes
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