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Announcements

  • CSI-Link: Research Box

    • DUE: Monday, 11/25 @ 11:59 pm; FRQ for Module 3 Exam (50 pts)

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  • Recommended Reading from textbook for Wednesday, 11/20: Chapters 19.1 – 19.3.

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    • Students with accommodations must schedule their appointment with SAS before Monday, 12/2/24 @ 9 am!

Lecture 16: Control of Gene Expression in Bacteria

18.1 Gene Expression Regulation Methods

  • Three ways gene expression can be regulated:

    1. Transcriptional Control

    2. Translational Control

    3. Post-Translational Control

  • Benefits of each method: Considerations of response time vs energy efficiency.

18.2 The lac Operon

  • Glucose's Effect: Explain its impact on negative and positive control of transcription.

  • Operon Structure: Recognize, draw, and label components, indicating regulatory protein binding regions.

  • Roles of lac I gene product and CAP: Expressed constitutively.

  • Compare Negative Control of lac and trp Operons.

  • Predict Impact of Operon Changes on gene expression.

18.3 Global Gene Regulation vs Single Operons

  • Global Gene Regulation: Defines how multiple operons are simultaneously regulated.

  • Regulons: Functions and regulatory control (negative and positive).

  • Effects of Regulons Changes on expression.

11.4 Quorum Signaling in Unicellular Organisms

  • Role of Quorum Sensing: Detecting population density and triggering responses.

Gene Expression Overview

  • The process includes transcription to produce RNA and protein.

  • Regulation of gene expression determines gene activation timing and protein quantity.

Mechanisms of Gene Expression Regulation

  1. Transcriptional Control: Changes frequency of transcription initiation.

  2. Translational Control: Alters translational rate.

  3. Post-Translational Control: Modifications of protein post-creation.

Transcription Regulation in Bacteria

  • RNA Polymerase: Holoenzyme that interacts with regulatory proteins at specific DNA sites

  • Regulatory Proteins: DNA-binding proteins that modulate transcription rates.

Negative and Positive Control

  • Negative Control: Transcriptional repressors decrease frequency.

  • Positive Control: Activators increase transcription frequency.

Model System: lac Operon

  • Lactose Metabolism in E. coli: Glucose is the preferred carbon source.

    • Lactose utilization occurs with low glucose.

    • Enzymes lacY and lacZ required for effective lactose metabolism.

Bacterial Chromosome Background

  • Operon: Clustered genes transcribed together.

  • Regulatory DNA Sequences: Bind regulatory proteins.

lac Operon Details

  • Repressor and Operator: Bind lactose and regulate transcription.

lac Operon Activation

  • Conditions that activate include high lactose and low glucose.

  • Relations between cAMP, CAP, and repressor effects on transcription.

Predicting Operon Effects

  • Outcomes of genetic mutations and repressor placements on transcription rates.

18.2 The trp Operon

  • Mechanisms for tryptophan synthesis regulation and responses to tryptophan's presence.

Learning Checks

  • Predictions for regulatory effects based on environmental conditions.

Global Control of Gene Expression

  • Regulons: Defined sets of genes influencing bacterial response.

Quorum Signaling Role

  • Bioluminescence in Vibrio fischeri: triggers collective behaviors in response to density.

  • Example of Pathogenic Quorum Sensing in Bacteria: Activation of virulence genes at high cell density.

Summary

  • Control of gene expression in bacteria focuses on transcriptional regulation via complex interactions between operons and regulatory proteins.

  • Understanding the lac operon serves as a foundation for broader applications in molecular biology.