1. Homework #2 is posted and due 10/17
Exams should be returned on W 10/3

2. Each step in gene expression presents an opportunity to regulate when and how much of a gene product will be produced.

3. Why change gene expression?
Different cells need different components
Responding to the environment
Replacement of damaged/worn-out parts

4. Two points to keep in mind:
Cellular components are constantly turned-over.
Gene expression takes time:
Typically more than an hour from DNA to protein. Most rapidly 15 minutes.

5. DNA damage inhibits rRNA transciption
Fig 1a
The ATM repair pathway inhibits RNA polymerase I transcription in response to chromosome breaks Nature Vol 447 pg (7 June 2007)

6. In bacteria, transcription and translation occur simultaneously
In bacteria, transcription and translation occur simultaneously. So most regulation of gene expression happens at transcription.
Fig 8.11

7. Transcription initiation in prokaryotes: sigma factor binds to the -35 and -10 regions and then the RNA polymerase subunits bind and begin transcription
Fig 8.8

8. Operon: several genes whose expression is controlled by the same promoter
Fig

9. E. coli lactose metabolism
Fig 10.5
E. coli lactose metabolism

10. In the absence of lactose, the lac operon is repressed.
Fig 10.6
In the absence of lactose, the lac operon is repressed.

11. Fig 10.6
Lactose binds to the repressor, making it inactive, so that transcription can occur.

12. Fig 10.6

13. Glucose is a better energy source than lactose
Fig 10.13

14. Low glucose leads to high cAMP
cAMP binds to CAP which increases lac operon transcription
Fig 10.13

15. High glucose leads to low cAMP
low cAMP, CAP inactive, low lac operon transcription
Fig 10.13

16. The lac operon: one example of regulating gene expression in bacteria
Fig