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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.

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slide2

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

slide5
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

slide6
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

slide8
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

slide9
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

slide10
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
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 repression12
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

slide13
Animation: The lac operon

The E. coli Lactose Operon

Click box to launch animation

slide15
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

slide21
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

slide23
Animation: Transcriptional Attenuation

Transcriptional Attenuation

Click box to launch animation

slide24
Animation: Chemotaxis: Molecular Events

Chemotaxis: Molecular Events

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slide25
Animation: Quorum Sensing

Quorum Sensing

Click box to launch animation