1. Control of Transcription DNA has “on” and “off” switches Activator –protein that binds near gene’s promoter region - allows RNA polymerase to transcribe (allows it to fit) Repressor – protein that binds to DNA and prevents RNA polymerase from binding -coded for by “regulator” gene

2. The Operon Model Operon – region of DNA with group of genes for proteins with related functions (see diagram) -All of the genes in the operon are controlled by activity at the promoter & the operator

3. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Promoter for I gene Gene for repressor protein Regulatory regionCoding region CAP-binding site Gene for permease Operator Promoter for lac operon Gene for  -galactosidase Gene for transacetylase PIPI CAP O Z Y A P lac I lac control system

4. The “Lac” Operon -in E. coli bacteria -genes for enzymes to break down lactose sugar 1. Regulator gene codes for Lac repressor protein 2. Repressor binds with operator region If no lactose present: 3. RNA polymerase can not bind to promoter, no enzyme made and operon is “off” If lactose is present: 3. Lactose binds with repressor, repressor no longer binds to operator 4.RNA polymerase transcribes the structural genes 5.Translation occurs, enzymes are made 6.Lactose is metabolized *Conservation of resources – enzymes only made when needed*

5. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Repressor CAP PromoterOperator cAMP RNA polymerase O Y A I Z lac operon is "repressed" P lac

6. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. lac operon is "induced" CAP PromoterOperator Allolactose (inducer) cAMP P lac RNA polymerase O Y A I Z

9. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. mRNA synthesis CAP- binding site RNA-polymrase binding site (promoter) Operator lacZ gene Operon ? because CAP is not bound Operon ? both because lac repressor is bound and CAP is not Operon ? because lac repressor is bound Operon ? because CAP is bound and lac repressor is not RNA polymerase Repressor RNA polymerase CAP + + + + Glucose Lactose – –– –

10. RNA in Gene regulation “Small RNA’s” Process of RNA interference (RNAi) or “RNA silencing” -double stranded RNA is cut into small pieces by enzyme called dicer -pieces then unravel into single strands 1. miRNA – micro RNA -binds to a specific RNA thus blocking it from being translated -reversible 2. siRNA – small interfering RNA -binds to specific mRNA, destroys it Purposes: (evolutionary origins) 1. Inactivate viral DNA transcription 2. Inactivate transposons – renegade “jumping genes” 3. Regulation

11. Nucleosomes

12. X- Inactivation