1. Transcriptional
Regulation in
Prokaryotes

2. Transcriptional Regulation in Prokaryotes
Why might a prokaryote need to regulate gene expression?
Metabolism based from external food sources

3. Operons in Bacteria
Operons: Clusters of genes that are under the control of the same promoter. The clusters of genes often control the same metabolic pathways.
Why would operons be advantageous?

4. Operons in Bacteria
Operons: Clusters of genes that are under the control of the same promoter. The clusters of genes often control the same metabolic pathways.
Why would operons be advantageous?
To facilitate coordination of gene expression
Bacteria are reliant on what ever food source is available

5. Operons in Bacteria Operons produce a polycistronic mRNA product
The same mRNA contains 3 different proteins

11. The lac Operon

12. The lac Operon Lac Operon is regulated by levels of glucose or lactose
Glucose is the preferred metabolite
Lactose will be used if glucose levels are low
B-Galactosidase (B-gal)

13. The lac Operon Lac Operon is regulated by levels of glucose or lactose
Glucose is the preferred metabolite
Lactose will be used if glucose levels are low
Would glucose positively or negatively regulate the lac operon?
Would lactose positively or negatively regulate the lac operon?

14. The lac Operon Lac Operon is regulated by levels of glucose or lactose
Glucose is the preferred metabolite
Lactose will be used if glucose levels are low
Would glucose positively or negatively regulate the lac operon?
Presence of glucose: Negative regulation
Lac operon off
Would lactose positively or negatively regulate the lac operon?
Presence of lactose: Positive regulation
Lac operon on

15. The lac Operon 15

16. The lac Operon 16

17. The lac Operon 17

18. The lac Operon 18

19. The Lac Operon: Regulation of a Repressor
Figure 18-6
The Lac Operon: Regulation of a Repressor
Lactose Absent
Lactose Present
allolactose useable form of lactose 19

20. Lac Operon: Regulation of the activator CAP
II. cAMP positively regulates the CAP activator
High glucose=low cAMP
Since glucose is present, transcription of lac genes are not needed.
No CAP activator recruitment
Low glucose=high cAMP
Since glucose is low, lactose can be utilized.
The CAP activator and cAMP interact which allows the CAP activator sequence to bind to the promoter region.
The CAP protein can then recruit RNA poly
CAP Activator recruits RNA poly
CAP Activator