Microbial Genetics Notes

Learning Outcomes Section 8.1

  • Define Terms
    • Genome: All the genetic information in a cell.
    • Gene: A segment of DNA that encodes functional products, usually proteins.
  • Genotype vs. Phenotype
    • Genotype: The sum of all gene types; an organism’s distinctive genetic makeup.
    • Phenotype: The expression of certain traits (structures or functions).
  • DNA Structure
    • DNA is composed of nucleotides, which consist of:
    • Phosphate
    • Deoxyribose sugar
    • Nitrogenous base
    • Formed into a double helix with a sugar-phosphate backbone.
    • Directionality: 5' to 3' and 3' to 5' strands.
  • Bacterial DNA Replication
    • Overall process: Semiconservative replication using 30 different enzymes.
    • Key Enzymes:
    • Helicase: Unzips DNA helix.
    • Primase: Synthesizes RNA primers.
    • DNA Polymerase: Adds bases to the new DNA chain; proofreads.
    • Ligase: Joins Okazaki fragments.
    • Topoisomerases: Prevents supercoiling.
    • Steps:
    1. Helicase unwinds DNA creating a replication fork.
    2. Single-stranded binding proteins stabilize unwound strands.
    3. DNA polymerase synthesizes leading strand continuously; synthesizes lagging strand in Okazaki fragments.
    4. RNA primers are replaced by DNA bases.
    5. DNA ligase joins fragments.
  • Central Dogma of Molecular Biology
    • Process: DNA → mRNA → Protein.

Learning Outcomes Section 8.2

  • Transcription and Translation
    • Transcription: DNA code is transcribed to synthesize RNA.
    • Translation: mRNA is translated to produce protein.
  • RNA Types:
    • Messenger RNA (mRNA): Carries code from DNA to ribosomes.
    • Transfer RNA (tRNA): Transfers amino acids during protein synthesis and contains anticodons.
    • Ribosomal RNA (rRNA): Integral part of ribosomes.
  • Codons:
    • Groups of three nucleotides on mRNA that dictate amino acid addition.
    • Start Codon: AUG (Methionine).
    • Stop Codons: UAA, UAG, UGA.
    • Anticodon: Complementary to mRNA codon on tRNA.
  • Transcription Steps:
    1. Initiation: RNA polymerase binds at the promoter.
    2. Elongation: RNA strand synthesized in the 5' to 3' direction.
    3. Termination: RNA polymerase reaches termination sequence, releases mRNA.

Learning Outcomes Section 8.3

  • Operons:
    • Genetic units in bacteria composed of coordinated genes regulated as one unit.
    • Types:
    • Inducible Operons: Activated in response to substrate (e.g., Lac operon).
    • Repressible Operons: Turned off by the product synthesized (e.g., Trp operon).
  • Lactose Operon Overview:
    • Components:
    1. Regulator: Produces repressor protein.
    2. Promoter: RNA polymerase binding site.
    3. Operator: On/off switch for gene expression.
    4. Structural Genes: Code for enzymes to break down lactose.
    • Mechanism:
    • Without lactose, repressor binds operator, blocking transcription.
    • With lactose, it binds to the repressor, allowing RNA polymerase to transcribe structural genes.
    • Enzymes produced only when lactose is present; synthesis stops when lactose is depleted.

Important Terms and Definitions

  • Nucleotide: Basic unit of DNA, consisting of a phosphate, a sugar, and a nitrogenous base.
  • Antisense RNA: RNA that can inhibit translation by binding to mRNA.
  • Micro RNA: Small RNA molecules that regulate gene expression.
  • Riboswitches: Segments of mRNA that regulate gene expression in response to small molecule binding.

Conclusion

  • Understanding microbial genetics is crucial for comprehending how genetic information is stored, replicated, and expressed in bacterial cells. This includes knowledge of DNA structure, replication processes, transcription, translation, and genetic regulation via operons.