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 Regulatory proteins  bind to operons to promote or inhibit the transcription of transcription unit (single mRNA coded in the operon)

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

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

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

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!