Daily Warm-Up Tuesday, Jan. 7th -Describe a signal transduction pathway. What are the three steps? (Hint: see Ch. 5) HW: -Read 15.1 Turn In: -Transformation lab questions

Gene Expression Why must genes be regulated? Transcription is most Environmental changes, energy cost (EVOLUTION!!!!!!!) Transcription is most common for control Prokaryotes and eukaryotes!!!! House-keeping genes transcribed always

Meet E. Coli Protein synthesis depends on our diet Ex. Tryptophan levels and lactose digestion

Levels of Control Control enzyme activity Feedback inhibition Control production of enzymes (gene expression)

Introducing…the Operon Promoter- remember this? Operator- segment of DNA that acts as an on/off switch Genes Tryptophan synthesis is performed by several enzymes. The genes for these enzymes are located next to each other.

Coordinately controlled

Turning off a gene Repressor Attaches to operator and prevents binding by RNA polymerase What does this do? Product of a regulatory gene (repressor) located away from gene

How do we turn a repressor off? Active and inactive form Need substrate

Negative Gene Regulation What do you think this results in? Stops gene regulation/production of product Operons turned off by activated repressors 2 Types: Repressible Inducible

Lac operon as an example of inducible

Positive Gene Regulation Activator- protein that binds to DNA and stimulates transcription