(469) 2117 Chapter 8 Part B - Microbial Genetics

Chapter 1: Intro

• Overview of Microbial Genetics

  • Bacterial cells carry out numerous metabolic reactions

  • Common feature: utilization of enzymes (proteins synthesized via transcription and translation)

  • Mechanisms to prevent synthesis of unwanted enzymes

  • Many genes (60-80%) are constitutive and not regulated, always "turned on"

Chapter 2: Constitutive Genes

• Definition and Characteristics

  • Constitutive genes: Not regulated, expressed at a fixed rate

    • Always "turned on"

  • Inducible genes: Normally off, must be turned on as needed

  • Repressible genes: Normally on, must be turned off as needed

• Importance in Cellular Function

  • Housekeeping and regulatory genes are usually constitutive

  • Conserves energy by expressing proteins only as needed

• Expression Control

  • Gene expression can occur during transcription (transcriptional control), translation (translational control), or post-translational control

  • Regulation helps manage energy usage during protein synthesis

Chapter 3: The Operon Model of Gene Expression

• Components of the Operon Model

  • Promoter: Segment of DNA where RNA polymerase initiates transcription

  • Operator: Segment of DNA that controls transcription of structural genes

  • Operon: Set of operator and promoter sites with the structural genes they regulate

• Example: Inducible Lac Operon

  • Operon example that highlights gene transcription regulation based on the presence of substrates

Chapter 4: Inducible Operons

• Inducible genes are not transcribed unless an inducer (e.g. lactose) is present

• Mechanism

  • In absence of lactose, a repressor binds to the operator, inhibiting transcription

  • Presence of lactose inactivates the repressor, allowing RNA polymerase to bind and promote transcription

• Key takeaways

  • Enzymes for lactose utilization are synthesized only in the presence of lactose

Chapter 5: Changes in Genetic Material

• Mutation Overview

  • Definition: Permanent change in the base sequence of DNA

  • Types of mutations: neutral, beneficial, or harmful

• Mutagen Sources

  • Agents that cause mutations (e.g., chemical mutagens, spontaneous mutations)

  • Commonly arise from errors in DNA replication and cell division

• Mutation Effects

  • Can impact cell function, including biofilm formation, pathogenicity, and antibiotic resistance

  • Beneficial mutations can drive evolution through natural selection

• Types of Mutations

  • Base substitution/Point mutation: Affects a single nucleotide change; can be neutral, missense (change in amino acid), or nonsense (premature stop codon)

  • Frameshift mutations: Insertion or deletion of nucleotides alters reading frame affecting downstream protein synthesis

Chapter 6: Radiation Effects

• Types of Radiation that cause mutations

  • Ionizing radiation: (X-rays, gamma rays) creates ions that can oxidize nucleotides and break DNA backbone

  • UV radiation: Causes thymine dimers, which can be repaired by photolyases

Chapter 7: Genetic Recombination and Transfer

• Importance of Recombination

  • Increases genetic diversity and drives evolution

• Mechanisms of Horizontal Gene Transfer

  • Transformation: Uptake and incorporation of naked DNA from the environment

    • Griffith's experiment demonstrated transformation with encapsulated bacteria

  • Transduction: Gene transfer from a donor to a recipient via a bacteriophage

    • Generalized transduction: random bacterial DNA packaging

    • Specialized transduction: specific bacterial genes packaging

Chapter 8: Conjugative Plasmids

• Definition and Role

  • Plasmids: Self-replicating circular DNA with additional genes (e.g., for antibiotic resistance)

  • Conjugative plasmids: Carry genes for sex pili and plasmid transfer

• Types of Plasmids

  • Dissimilation plasmids: Encode enzymes for unusual compound catabolism

  • Resistance factors (R factors): Encode antibiotic resistance

Chapter 9: Genes and Evolution

• Role of Genetic Diversity

  • Mutations and recombination create cell diversity, essential for evolution

• Natural Selection Process

  • Variation within populations leads to competition for resources

  • Better-adapted individuals pass genes to offspring, fostering survival and reproductive success

  • Example: Giraffe neck length evolution due to environmental advantages

• Summary of Evolution Theory

  • Variability, heritability, success in survival leads to population evolution

  • Evolution driven by mistakes (mutations) shaping diversity and adaptation in life forms