1. Regulation of gene and cellular activity

2. Regulating Gene Expression
Cells use different mechanisms to sense and respond to conditions within or outside the cell.
Regulatory proteins help a cell sense internal changes and alter its gene expression to match.
Figure 10.1A

3. Figure 10.1B and C 3

4. Figure 10.3 4

5. Regulating Gene Expression
Microbes control gene expression at several levels:
- Alterations of DNA sequence
- Control of transcription
- Control of mRNA stability
- Translational control
- Posttranslational control 5

6. The E. coli Lactose Operon
The lactose utilization lacZYA operon of E. coli was the first gene regulatory system described.
First, here’s how lactose is transported and metabolized.
Figure 10.6 6

7. The Organization of the LacZYA Operon
Figure 10.5A 7

8. Scenario 1: Absence of Lactose
LacI binds as a tetramer to the operator region.
- It represses the lac operon by preventing open complex formation by RNA polymerase.
Figure 10.5B 8

9. Scenario 2: Presence of Lactose
b-galactosidase (LacZ), when at low concentrations, cleaves and rearranges lactose to make the inducer allolactose.
Allolactose binds to LacI, reducing its affinity to the operator and thus allowing induction of the operon.
Figure 10.5C 9

10. Activation of the lac Operon by cAMP-CRP
Maximum expression of the lac operon requires the presence of cAMP and cAMP receptor protein (CRP).
- The cAMP-CRP complex binds to the promoter.
- Interacts with RNA pol to increase the rate of transcription initiation
Figure 10.8 10

11. Catabolite Repression
In catabolite repression, an operon enabling the catabolism of one nutrient is repressed by the presence of a more favorable nutrient (commonly glucose).
The biphasic curve of a culture growing on two carbon sources is often called diauxic growth.
Figure 10.10 11

12. Catabolite Repression
Glucose transport by the phosphotransferase system causes catabolite repression by inhibiting the LacY permease activity.
- This is termed inducer exclusion.
Figure 10.11 12

13. Click box to launch animation
The E. coli Lactose Operon
Animation: The lac operon
Click box to launch animation

14. Figure 10.15 14

15. Attenuation of the trp Operon
Attenuation is a regulatory mechanism in which translation of a leader peptide affects transcription of a downstream structural gene.
The attenuator region of the trp operon has 2 trp codons and is capable of forming stem-loop structures.
Figure 10.16A 15

16. The Transcriptional Attenuation Mechanism of the trp Operon
Figure 10.16B and C 16

17. Figure 10.18 17

18. Figure 10.24 18

19. Figure 10.26A 19

20. Figure 10.28 20

21. Quorum Sensing
Quorum sensing refers to the process where bacterial cells work together at high density.
- It was discovered in Vibrio fischeri, a bioluminescent bacterium that colonizes the light organ of the Hawaiian squid.
Figure 10.30ACD 21

22. Figure 10.31 22

23. Click box to launch animation
Transcriptional Attenuation
Animation: Transcriptional Attenuation
Click box to launch animation

24. Click box to launch animation
Chemotaxis: Molecular Events
Animation: Chemotaxis: Molecular Events
Click box to launch animation

25. Click box to launch animation
Quorum Sensing
Animation: Quorum Sensing
Click box to launch animation