BOLOGY 107 Lecture 30Outline of Last Lecture I. Gene Expressiona. Translation (cont.)b. Protein targetingc. PolyribosomesII. Mutationsa. What they areb. How they ariseOutline of Current Lecture III. Gene Regulationa. Prokaryotic gene regulationb. Lac OperonCurrent LectureGene Regulation1) Regulation of when, where, and how much a gene is expresseda) Every cell has the same DNA, must be expressed differently for each cellb) Biochemical pathways are regulated by:i) Regulating enzyme activity (feedback)ii) Regulating enzyme production (expression)2) Prokaryotic gene regulationi) Focuses for the cells:(1) Energy conservation(2) Respond to the environmentii) Operons(1) A cluster of functionally related genes and the sequences that control them(a) Genes are transcribed as a unit into a single mRNA(b) mRNA translated into multiple proteins(i) Prokaryotes and viruses(2) Regulatory proteins respond to biochemical signals to turn Operon on or off(3) Allows for coordinated regulation on genes in a single pathway(4) Transcription regulation of OperonThese 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.(a) Sequences (i) Promoter- RNA polymerase binding site and transcription start site(ii) Operator- sequence near promoter that binds to the repressor(iii) Repressor- protein that binds to the operator to block RNA polymerase1. Corepressor- small molecule that binds to the repressor and allows it to block transcription2. Inducer- small molecule that binds to the repressor and prevents it from blocking transcription3) Lac Operona) Some organisms, like E. coli can use lactose as an energy sourcei) Can only use it when lactose is present and glucose is not(1) Lactose is split into glucose and galactoseb) Lac Operon is made of three genes for lactose metabolismi) LacZ = β-galactosidase, cleaves lactose or rearranges it to allolactoseii) LacY = lactose permease, allows lactose into the celliii) LacA = transacetylase, acetylates β-glactosidase to modify its activityc) Negative regulation- promoter is turned off when substrate is absenti) Lac I – the Lac repressor blocks transcription when there is no lactose(1) Lac repressor binds to operator, preventing transcription(a) “Leaky” block- a little bit of β-galactosidase is made, converts lactose to allolactose(i) Allolactose indicates lactose is present(b) Allolactose is an inducer that inactivates Lac repressor(i) Allosteric regulation- changes shape so it cannot bindii) Cells do not waste energy making enzymes for a substrate that is not presentd) Positive regulation- promoter is turned on when energy is neededi) CAP- catabolite activator protein increases promoter function when glucose islow(1) cAMP is a cellular indicator for low glucose, binds to CAP(2) CAP binds to the activator sequence adjacent to promoter(3) RNA polymerase binds ro CAP to be loaded onto the promoterii) Cells do not waste energy making glucose from lactose if glucose is
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