2. G ENE R EGULATION The turning on and off of genes Allows organisms to respond to environmental changes Ex: lac Operon in bacteria

4. E. C OLI AND L ACTOSE E. coli uses 3 enzymes to metabolize lactose. 2 control sequences are located next to the lactase enzymes Promoter – site where RNA polymerase attaches and initiates transcription Operator – acts as a switch (determining whether RNA polymerase can attach to promoter and start transcription)

6. O PERON A cluster of genes with related functions, promoter, and an a operator Occurs in prokaryotes

7. R EPRESSOR Protein that functions by binding to the operator Blocks the attachment of RNA polymerase to the promoter region Molecule that turns off transcription Cells have a regulatory gene to make the repressor

9. A CTIVATORS Proteins that turn operons on by binding to DNA Makes it easier for the RNA polymerase to bind to the promoter Allows bacteria to survive in frequently changing environments.

10. E UKARYOTES AND G ENE E XPRESSION Each eukaryote gene has its own promoter and other control sequences The default state for most genes tend to be “off”