Regulation of gene and cellular activity

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

Figure 10.1B and C 3

Figure 10.3 4

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

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

The Organization of the LacZYA Operon Figure 10.5A 7

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

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

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

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

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

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

Figure 10.15 14

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

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

Figure 10.18 17

Figure 10.24 18

Figure 10.26A 19

Figure 10.28 20

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

Figure 10.31 22

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

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

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