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Understanding Microbial Genetics and Genomics

May 9, 2025

Lecture on Genetics and Microbial Genomics

Overview of Gene Function

  • Gene Function: Codes for specific proteins.
  • Genetics of Microbes: Focus on microbial DNA.
    • Bacterial DNA: Circular, single chromosome (nucleoid) in cytoplasm.
    • Eukaryotic DNA: Linear chromosomes inside nucleus.

Genome Structure

  • Genome: All genetic material in an organism.
  • Chromosomal vs. Extrachromosomal DNA
    • Chromosomal DNA: Majority of genetic material; humans have 46 chromosomes.
    • Extrachromosomal DNA: Found in mitochondria (single circular chromosome), chloroplasts (in plants), and plasmids.
  • Plasmids: Small circular DNA in prokaryotes, sometimes eukaryotes; can transfer genes between organisms.
  • Viruses: Can contain DNA or RNA genomes, but not both.

Genetic Material and Its Components

  • DNA and RNA: Made of nucleotides.
    • Nucleotide Components: Phosphate group, sugar (deoxyribose in DNA, ribose in RNA), nitrogenous bases (A, T, C, G for DNA; A, U, C, G for RNA).
  • DNA Structure: Double helix with anti-parallel strands; base pairing (A-T and C-G).

Central Dogma of Genetics

  • Flow of Genetic Information: DNA -> RNA -> Protein.
    • Transcription: DNA is transcribed to mRNA.
    • Translation: Ribosomes translate mRNA to proteins.

Differences in Gene Expression

  • Eukaryotic Gene Expression
    • Occurs in nucleus; involves RNA processing (splicing, capping, polyadenylation).
    • Translation occurs in cytoplasm.
  • Prokaryotic Gene Expression
    • Occurs in cytoplasm; transcription and translation can happen simultaneously.
    • No RNA processing needed.

Operons in Prokaryotes

  • Definition: Set of functionally related genes regulated together.
  • Types of Operons
    • Inducible Operons: Normally off, turned on by a substrate (e.g., Lac operon by lactose).
    • Repressible Operons: Normally on, turned off by product accumulation (e.g., Arginine operon).

Horizontal Gene Transfer

  • Recombination: Exchange of DNA between bacteria.
  • Types of Horizontal Gene Transfer
    • Conjugation: DNA transfer via sex pilus.
    • Transformation: Uptake of naked DNA from environment.
    • Transduction: DNA transfer via bacteriophages.
  • Plasmids in Gene Transfer: Often convey antibiotic resistance, virulence factors.

Mutations and Their Impact

  • Mutations: Changes to DNA sequence.
    • Spontaneous Mutations: Random errors during DNA replication.
    • Induced Mutations: Caused by mutagens (chemical, radiation).
  • DNA Repair: Photoactivation can repair UV-induced damage.

Ames Test

  • Purpose: Identify mutagenic/carcinogenic chemicals.
  • Procedure: Uses specific strains of bacteria to observe mutation rates in presence of test chemicals.
  • Interpretation: Increased mutation rate indicates mutagenicity.

This lecture covered foundational concepts in microbial genetics, focusing on the structure and expression of genetic material, differences between prokaryotic and eukaryotic systems, and the mechanisms of gene transfer and mutation. These insights are crucial for understanding microbial function and evolution.

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