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Regulation of Protein Expression.docx

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Jeff Stuart

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Regulation of Protein ExpressionChapter 2January1714930 AMWhat is meant by protein activityCould be force generation rate of a chemical reaction for enzyme movement of moleculesCellular Activity vs Specific ActivitySpecific activityamount of event performed per unit time per molecule of that proteinThis is difficult to measure as the protein would need to be pure and nothing else in systemTotal activity amount of event per unit time per cell or unit tissue massWe usually measure this oneHow to change the rate of a proteins overall cellular activityChange the specific activity of the protein or change the amount of the proteinImportant things to considerWhat rate of change is required You can rapidly degrade a protein it takes a long time to transcribe and translate there may be thousands of nucleotides that are transcribed which then need to be transported to the area needed it tends to happen slow as so much needs to occurDo activities of any other proteins need to be changed simultaneously Regulation of the Specific ActivityPosttranslational ModificationsAffects existing proteins does not change amount but change specific activityoAll parts of the cell are continuously degrading to do enthalpyoOxygen causes problems etcCan be rapidCan be short or long livedoAs a general rule they are all reversibleoKinase phosphatase always go together both are changeable often part of a protein complexMultiple proteins may be affectedoThere are thousands of kinasesoMany of these kinases have diverse substrates recognise a particular amino acidMultiple modifications are possible within a proteinoThis can be measured antibodies can recognise a variety of proteins under a specific condition such as a phosphorylated proteinMust be reversible to be regulatory exception ubiquitation Reversible PhosphorylationThe first example historicallymobilization of glucose from glycogenWhen skeletal muscle becomes active really abruptly the glycogen is rapidly depolymerized the enzyme that does that is normally turned off so within seconds it needs to be turned onStored in the muscles and liverThe enzyme glycogen phosphorylase releases individual subunits of glucose from the polymer glycogenA single phosphorylation event of that enzyme is enough to turn it on or offNeed ATP and phosphorylase kinase to add a P to glycogen phosphorylaseATP cleaved to ADP the P released is covalently attached to a protein glycogen phosphorylase in the exampleA phosphotase will always be matched with a phosphylaseAlways with the following amino acids serine tyrosine threonine all have an OH group on the R group Reversible Acetylation
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