1. 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

2. 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

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

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

5. 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.

6. Coordinately controlled

7. 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

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

9. 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

10. Lac operon as an example of inducible

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