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Gene expression is controlled on multiple levels • Transcriptional, translational, and post translational control• Transcriptional control saves the most energy but takes a long time to respond• Post translational is the fastest but is the most energy inefficientClusters of bacterial genes controlled together are called operons• Operon includes both promoter, operator, and structural genes• Regulatory genes are not part of the operon • Regulatory genes vs structural genes• Structural genes are transcribed and translated• Regulatory genes may be transcribed and translated but they regulate the genes that are expressed• Genes vs gene products• Genes are lowercase and italicized• Gene products have a capital first letter and are not italicized• Regulatory genes vs regulatory sequences• Regulatory genes interact with regulatory sequences• Regulatory sequences are specific stretches of DNA that can be modified to change expression• Studied by identifying mutants• Negative sign jeans mutant• This us not directly observed - it is a modelSome regulatory genes produce products that interact with regulatory regions and repress transcription• Negative control shuts down transcription• Repressor protein binds to regulatory sequence (operator)lac operon lactose will bind to Repressor and allow transcription to occurSome regulatory ends produce products that stimulate transcription of other genes• Activator protein binds to initiator and speeds up transcription of the operonPresence of glucose interferes with the movement if lactose in the cell• Glucose interferes with lactose's ability to go through poresTrp encodes three enzymes that are involved in biosynthesis in tryptophan Trp operons regulatory gene trpR is far upstream of the operon and encodes a Repressor protein that is usually inactive Without tryptophan the Repressor can not bind to the operatorWhen tryptophan is present the Repressor can bind to the operatorIn the presence of arabinose, the activator binds to the initiatorIn the absence of arabinose the AraC protein blocks itself from being produced• The same Repressor can work at multiple operons leading to lots of genes being regulated• One Repressor protein can act in multiple places in the genomeInformation flow is more complicated in eukaryotes providing more opportunities for control• mRNA needs more processing in eukaryotes• mRNA must also be moved• Opportunities for eukaryotic control• In the nucleus:• Access to DNA • Transcription regulation• Processing of transcript• In the cytoplasm:• Degrading mRNA• Speed and number of translations• Post translational processing• DNA is highly packaged and is mostly inaccessible• DNA is wound around his tones to form nucleosomes• Chromatin is DNA + histones• 8 histones are in one nucleosome• DNA backbone had a negative charge, histones have a positive surface charge• Linked DNA is exposed• Acetyl groups added of histones open the chromatin and expose more DNA • Elements of eukaryotic genes are more or less exposed based on the chromatin remodelingImplications of chromatin remodeling• Remodeling (changes in groups added to histone proteins) can be pretty stable over time• The signal of which genes to express can be passed to daughter cells• There may be a histone code• Epigenetic inheritance (patterns of inheritance not due to differences in DNA sequence) break the rules of central


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Pitt BIOSC 0160 - Lecture notes

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