LS9Prokaryotictranscription

LS9Prokaryotictranscription - Lecture 9: Prokaryotic Gene...

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1 Lecture 9: Prokaryotic Gene Regulation Jacob and Monod the lac operon Rotations of bacterial flagella
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2 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)
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3 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
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4 Three levels of transcription: -basal level -repressed -activated -35 -10 DNA bending proteins can facilitate these distal interactions Activation by recruitment
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5 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 β -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
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LS9Prokaryotictranscription - Lecture 9: Prokaryotic Gene...

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