Regulation of gene and cellular activity

• 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.

Regulating Gene Expression

Figure 10.1A

Figure 10.1B and C

Figure 10.3

• 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

• 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

The Organization of the LacZYA OperonFigure 10.5A

• 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

• 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

• 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

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

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

• Animation: The lac operon

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The E. coli Lactose Operon

Figure 10.15

• Attenuation is a regulatory mechanism in which translation of a leader peptide affects transcription of a downstream structural gene.

Attenuation of the trp Operon

Figure 10.16A

The attenuator region of the trp operon has 2 trp codons and is capable of forming stem-loop structures.

The Transcriptional Attenuation Mechanism of the trp Operon

Figure 10.16B and C

Figure 10.18

Figure 10.24

Figure 10.26A

Figure 10.28

• 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

Figure 10.31

• Animation: Transcriptional Attenuation

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Transcriptional Attenuation

• Animation: Chemotaxis: Molecular Events

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Chemotaxis: Molecular Events

• Animation: Quorum Sensing

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Quorum Sensing