1. Genetics of Viruses and Bacteria Ch 18

2. Operon – consists of the operator, the promoter, and the genes Operator – “switch” controls transcription …repressor binding site Repressor – binds to operator and controls transcription by blocking the attachment of RNA Polymerase to the promoter

3. Corepressor – cooperates w/ repressor to switch the operon off. (*tryptophan controls the regulation of the gene by binding to the repressor when tryptophan is present….p338 Fig 18.19) Repressible enzymes – anabolic…build or synthesize end products from raw materials *Make end product if needed and suspend production if already present. *Tryptophan is a repressible operon usually on but can be repressed/inhibited when tryptophan binds to the repressor. http://highered.mcgraw- hill.com/olc/dl/120080/bio26.swf

4. Inducible enzymes- catabolic….break down into simpler molecules, inactivates the repressor. *lactose is an inducible operon….usually off but when stimulated/induced lactose binds to the repressor and mRNA is transcribed *present only when substrate is present.

5. http://vcell.ndsu.nodak.edu/animations/lacOp eron/movie-flash.htm http://highered.mcgraw- hill.com/sites/0072556781/student_view0/cha pter12/animation_quiz_3.html http://www.sumanasinc.com/webcontent/ani mations/content/lacoperon.html http://highered.mcgraw- hill.com/olc/dl/120080/bio27.swf http://phsgirard.org/APbiology/Chapter18/Lac Operon.mov