BOLOGY 107 Lecture 30 Outline of Last Lecture I Gene Expression a Translation cont b Protein targeting c Polyribosomes II Mutations a What they are b How they arise Outline of Current Lecture III Gene Regulation a Prokaryotic gene regulation b Lac Operon Current Lecture Gene Regulation 1 Regulation of when where and how much a gene is expressed a Every cell has the same DNA must be expressed differently for each cell b Biochemical pathways are regulated by i Regulating enzyme activity feedback ii Regulating enzyme production expression 2 Prokaryotic gene regulation i Focuses for the cells 1 Energy conservation 2 Respond to the environment ii 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 Operon These 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 polymerase 1 Corepressor small molecule that binds to the repressor and allows it to block transcription 2 Inducer small molecule that binds to the repressor and prevents it from blocking transcription 3 Lac Operon a Some organisms like E coli can use lactose as an energy source i Can only use it when lactose is present and glucose is not 1 Lactose is split into glucose and galactose b Lac Operon is made of three genes for lactose metabolism i LacZ galactosidase cleaves lactose or rearranges it to allolactose ii LacY lactose permease allows lactose into the cell iii LacA transacetylase acetylates glactosidase to modify its activity c Negative regulation promoter is turned off when substrate is absent i 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 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 bind ii Cells do not waste energy making enzymes for a substrate that is not present d Positive regulation promoter is turned on when energy is needed i CAP catabolite activator protein increases promoter function when glucose is low 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 promoter ii Cells do not waste energy making glucose from lactose if glucose is present
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