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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

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Page 1: Promoters and the Lac Operon. Regulation in Prokaryotes Adjust biochemistry quickly as environment changes Jacob and Monod  extensive studies into the

Promoters and the Lac Operon

Page 2: Promoters and the Lac Operon. Regulation in Prokaryotes Adjust biochemistry quickly as environment changes Jacob and Monod  extensive studies into the

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)

Page 3: Promoters and the Lac Operon. Regulation in Prokaryotes Adjust biochemistry quickly as environment changes Jacob and Monod  extensive studies into the

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

Page 4: Promoters and the Lac Operon. Regulation in Prokaryotes Adjust biochemistry quickly as environment changes Jacob and Monod  extensive studies into the

The lac Operon• 3 genes:1) lacZ codes for β-galactosidase;

breaks lactose into glucose + glactose

2) lacY codes for permease; actively transports lactose into the cell

3) 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

Page 5: Promoters and the Lac Operon. Regulation in Prokaryotes Adjust biochemistry quickly as environment changes Jacob and Monod  extensive studies into the

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 lac operon. 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

Page 6: Promoters and the Lac Operon. Regulation in Prokaryotes Adjust biochemistry quickly as environment changes Jacob and Monod  extensive studies into the

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!