Expressing all genes all the time is counterproductive because not all genes are needed in all situations and some contradict each other Bacteria Are Able to Contol When Genes Are Expressed Information in DNA is more like a recipe than a blueprint It is a collection of things that must be out together in a certain way Can t map exactly what comes out based on ingredients Control of Gene expression plays a central role in growth and development Specialization if cells is a result of gene regulation Small grafting of genome expressed in a cell at any given time Allows response to environmental changes Signal change in RNA changed cell behaviors and structures Gene regulation helps cells conserve energy Slide 7 match cells and gene expression Gene expression can be controlled at multiple levels in prokaryotes Transcriptional translational and post translational control There are two broad categories of genes to consider Structural genes Regulatory genes Code for proteins that act in structure or metabolism Code for RNA or proteins that regulate the expression of other genes by binding to DNA Some can produce products that repress transcription of other genes Negative control uses a regulatory protein to shut down transcription Repressor protein attaches to DNA Some can produce products that stimulate transcription of other genes Positive control triggers transcription Activator proteins attach to DNA and facilitate work of RNA polymerase lac operon has several genes that allow the cell to use lactose cid 127 Galactoside permeate let s lactose into the cell cid 127 Galactosidase digests lactose Structural genes in an operon at close together and form a transcriptional unit Can use one regulatory mechanism for both genes Regulatory genes are controlled separately and are not considered part of the operon Promoter signals start of transcription Signals start of lac operon but the repressor can still block transcription cid 127 When lactose is in the cell it will bind to the repressor and allow transcription to occur cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127
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