Regulation of gene and cellular activity

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

4. Figure 10.3

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

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

7. The Organization of the LacZYA Operon Figure 10.5A

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

9. 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. Scenario 2: Presence of Lactose Figure 10.5C

10. 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 Activation of the lac Operon by cAMP-CRP Figure 10.8

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

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

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

14. Figure 10.15

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

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

17. Figure 10.18

18. Figure 10.24

19. Figure 10.26A

20. Figure 10.28

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

22. Figure 10.31

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

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

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