Microbiology Chapter 8_EDITED

Chapter 8: Microbial Genetics

Structure and Function of Genetic Material

• Genetics: Study of genes, how they carry information, their expression, and replication.

• Gene: Segment of DNA encoding a functional product, typically protein.

• Chromosome: Structure containing DNA that carries hereditary information; contains genes.

• Genome: Complete genetic content of a cell.

• Genomics: Molecular study of genomes.

• Genotype: The genetic makeup of an organism.

• Phenotype: Observable expression of genes.

Prokaryotic Chromosome Structure

• Image Reference 8.1a: Depicts a disrupted E. coli cell's chromosome structure.

• Image Reference 8.1b: Genetic map of E. coli's chromosome showcasing various metabolic functions and processes.

Genetic Information Flow

• Figure 8.2: Overview of how genetic information within a cell is expressed to produce necessary proteins, involving processes of transcription and translation, including cell metabolism and growth.

DNA Structure

• Composition: DNA is a polymer of nucleotides (adenine, thymine, cytosine, guanine).

• Structure: Double helix with a deoxyribose-phosphate backbone; strands held together by hydrogen bonds between AT/CG pairs.

• Strand Orientation: Strands are antiparallel and complementary.

Transcription Process

• Definition: DNA is transcribed to produce RNA (mRNA, tRNA, rRNA).

• Steps:

  • Initiation: RNA polymerase binds to the promoter sequence.

  • Elongation: RNA strand is synthesized in the 5' to 3' direction.

  • Termination: Process ends at the terminator sequence.

• Figure 8.7: Shows RNA polymerase action from initiation to termination.

Translation Process

• Mechanism: mRNA is translated at ribosomes into proteins by tRNA carrying amino acids via codons.

• Key Points:

  • Begins at start codon (AUG), stops at nonsense codons (UAA, UAG, UGA).

  • The genetic code includes 64 codons for 20 amino acids, demonstrating degeneracy.

• Figures 8.9 and 8.10: Illustrate the sequential steps of translation from initiation, peptide bond formation, to termination.

Mutations

• Definition: Changes in genetic material that can be neutral, beneficial, or harmful.

• Types:

  • Spontaneous mutations: Occurs without mutagens.

  • Missense mutation: Alters one base, changing amino acid.

  • Nonsense mutation: Produces a stop codon due to base substitution.

  • Frameshift mutation: Caused by insertions or deletions that disrupt reading frames.

• Detection: Via experiments like the Ames test which evaluates mutagenic potential.

Genetic Transfer and Recombination

• Gene Transfer Methods:

  • Vertical Gene Transfer: Transmission during reproduction between generations.

  • Horizontal Gene Transfer: Transfer of genes between cells of the same generation, includes transformation, transduction, and conjugation.

  • Figures 8.24-8.29: Illustrate crossing over, transformation via naked DNA, and conjugation mechanism.

Plasmids and Transposons

• Plasmids: Circular DNA that can replicate independently; carry genes such as antibiotic resistance (0 R factors).

• Transposons: DNA segments that can move within the genome, facilitating genetic variation.

• Types of Transposons: Insertion sequences (simplest), complex ones carrying additional genes.

Conclusion: Genetics and Evolution

• Role in Evolution: Mutations and recombination increase diversity, providing material for natural selection, influencing organism adaptation.