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Promoters and the Lac Operon

Promoters and the Lac Operon. Regulation in Prokaryotes. Adjust biochemistry quickly as environment changes Jacob and Monod  extensive studies into the effects of lactose on expression of lactase genes Operon  regulatory sequence in DNA for a specific gene(s) + the genes

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Promoters and the Lac Operon

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  1. Promoters and the Lac Operon

  2. Regulation in Prokaryotes • Adjust biochemistry quickly as environment changes • Jacob and Monod extensive studies into the effects of lactose on expression of lactase genes • Operon regulatory sequence in DNA for a specific gene(s) + the genes • Regulatory proteins bind to operons to promote or inhibit the transcription of transcription unit (single mRNA coded in the operon)

  3. Regulation of an Operon • Operator section at the start of the operon • Promoter starting point of transcription • Activator protein attaches to operator to promote expression • Repressor protein attaches to operator to inhibit expression • Gene coding for regulatory proteins (activators/repressors) are called regulatory genes • Non-regulating proteins come from structural genes

  4. The lac Operon • 3 genes: • lacZ codes for β-galactosidase; breaks lactose into glucose + glactose • lacYcodes for permease; actively transports lactose into the cell • lacA codes for transacetylase; We don’t know what it does • Negatively regulated • Regulator gene lacI codes for Lac repressor • Limits lac expression when lactose is absent (normal) • When lactose is added, it is made into allolactose(inducer for lac operon) • Inhibits lac repressor by binding to it

  5. Lac Operon Part II; Positive Regulation • Lac operon is repressed in the presence of lactose if glucose is also added. Why? • Glucose is a better source of energy • Converting lactose into usable sugars (glucose) requires energy • First transformed bacteria for insulin production used the lacoperon. Why was this a poor choice? • Only makes insulin when in the a lactose solution • High levels of glucose (produce of lactose breakdown) will slow production

  6. Assignments for Next Week • PPT Presentations on Ch. 18: • Groups of 2; 5-8 min presentations • Topics: • Promoters in DNA (use Lac Operon as example) • PCR (how does it work? Why do we need it?) • Gel Electrophoresis (how does it work? Why use it?) • Screening Modified Bacteria (how do we know the right plasmid made it inside) • Please use lots of pictures/videos to help explain these topics • I want to see GOOD presentation skills • No LAZY PPTs full of text! • No READING the whole PPT!

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