08-lecture-presentation_Sp25

Microbial Genetics Overview

Chapter Overview

  • Chapter 8: Microbial Genetics

  • Focus on genetic material structure, function, and mechanisms guiding genetic processes.

Structure and Function of Genetic Material

Learning Objectives

  • Define key terms:

    • Genetics: Study of genes and how they carry and express information.

    • Genome: Complete set of genetic information in a cell.

    • Chromosome: DNA structures that carry hereditary information.

    • Gene: DNA segment encoding functional proteins.

    • Genetic Code: Rules for translating nucleotide sequences into amino acids.

    • Genotype vs Phenotype:

      • Genotype: Genetic makeup of an organism.

      • Phenotype: Observable expression of genes.

DNA Replication

Mechanism Overview

  • Topoisomerase and Gyrase: Relax DNA strands.

  • Helicase: Unwinds double-stranded DNA into two strands.

  • Semi-Conservative Replication: Each strand serves as a template for a new complementary strand.

  • Leading vs Lagging Strand:

    • Leading: Continuous synthesis.

    • Lagging: Discontinuous synthesis with Okazaki fragments.

Key Enzymes Involved

  • DNA Polymerase: Adds nucleotides to forming strands; proofreads DNA.

  • Helicase: Unwinds DNA.

  • Ligase: Joins Okazaki fragments.

  • Primase: Synthesizes RNA primers for replication initiation.

RNA and Protein Synthesis

RNA Types

  • rRNA: Component of ribosomes.

  • tRNA: Brings amino acids to ribosomes.

  • mRNA: Carries genetic code from DNA to ribosomes.

Transcription in Prokaryotes

  • Initiated by RNA polymerase binding to the promoter.

  • Synthesized in the 5' to 3' direction.

  • Terminates at a specific sequence called the terminator.

Translation Process

  • Initiation: Begins at the start codon (AUG).

  • Reading Codons: mRNA codons are read by tRNA, matching anticodons to codons.

  • Peptide Bonding: Amino acids are linked by peptide bonds to form polypeptides.

  • Continues until a stop codon is reached, releasing the newly formed protein.

Gene Regulation in Bacteria

Operon Concept

  • Operon: A cluster of genes controlled by a promoter and an operator.

  • Types of Genes:

    • Constitutive: Always active.

    • Inducible: Turned on by presence of specific substrates (e.g., lactose).

    • Repressible: Remains active until repressed by metabolites (e.g., tryptophan).

Mutations

Types of Mutations

  • Base Substitution: Single nitrogen base is replaced.

    • Silent Mutation: No change in protein.

    • Missense Mutation: Results in a different amino acid.

    • Nonsense Mutation: Produces a premature stop codon.

    • Frameshift Mutation: Addition or deletion of bases that shifts reading frame.

Mutagens

  • Agents inducing mutations:

    • Chemical mutagens (e.g., nitrous acid).

    • Radiation (e.g., UV light causing thymine dimers).

Genetic Transfer Mechanisms

Types of Transfer

  • Vertical Gene Transfer: From parent to offspring.

  • Horizontal Gene Transfer: Between organisms of the same generation.

    • Transformation: Uptake of "naked" DNA from the environment.

    • Conjugation: Transfer of DNA between bacteria via direct contact (sex pili).

    • Transduction: Transfer via bacteriophages, involving generalized or specialized forms.

Plasmids and Transposons

Plasmids

  • Plasmids: Circular, self-replicating DNA, smaller than chromosomes.

    • Types:

      • Conjugative: Impart genes for pili and plasmid transfer.

      • Dissimilation: Code for enzymes for unusual compound catabolism.

      • Resistance Factors (R factors): Carry genes for antibiotic resistance.

Transposons

  • Jumping Genes: Sequences that can move within and between DNA molecules.

  • Contain genes necessary for their movement (transposase).

Conclusion

Review Topics

  • Processes of DNA replication, transcription, and translation.

  • Distinctions between prokaryotes and eukaryotes in genetic processes.

  • Mutation types and DNA repair mechanisms.

  • Gene transfer techniques and their implications in genetic diversity.