Lecture 8

Lecture 8 - Regulation of Transcription Prokaryotes Jacob...

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Unformatted text preview: Regulation of Transcription Prokaryotes Jacob and Monod the lac operon Rotations of bacterial flagella 20 genes are needed to generate a bacterial flagellum Related genes are often organized as operons Operon - an arrangement of genes in a contiguous linear array In an operon a continuous strand of mRNA carries the message for a related series of enzymes (polycistronic mRNA) Why are genes organized into operons? Genes encoding enzymes in a common pathway can all be induced simultaneously. This type of control is called coordinate control . One mRNA expresses multiple proteins. Weak promoters have poor consensus sequences and initiate transcription infrequently Strong promoters generally have good consensus sequences and initiate transcription often Many promoters are regulated by additional regulatory proteins as well Repressors inhibit transcription initiation Activators increase transcription initiation Promoter sequence determines first level of regulation Three levels of transcription:-basal level-repressed-activated-35 -10 DNA bending proteins can facilitate these distal interactions Activation by recruitment RNA polymerase Repressor mRNA Repressors usually block transcription initiation by: interfering with RNA polymerase binding or preventing open complex formation The lac operon consists of three genes under the control of a single promoter. lacZ encodes -galactosidase, an enzyme that catalyzes the hydrolysis of lactose lacY encodes the lactose permease, required for transport of lactose into the cell lacA encodes a transacetylase of unknown function lacPromoter lacZ lacY lacA Levels of...
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Lecture 8 - Regulation of Transcription Prokaryotes Jacob...

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