microbial genetics

Viewing DNA Across Different Time Scales

  • Moment-by-Moment: Examines DNA in real time; includes processes like:

    • DNA Replication
    • Transcription
    • Translation

  • Generational: Focuses on multiple generations where DNA or genetics are passed down (parents to offspring), considering:

    • Evolutionary changes
    • Genetic recombination (mixing traits from parents)

  • Geological Time Scale: Explores DNA changes over millions to billions of years, involving:

    • Fossil DNA studies
    • Long-term evolutionary changes

Template Theory

  • Proposed that DNA replication requires a complementary template from which to replicate.
  • This theory posits that a single original strand of DNA serves as a template for creating new DNA strands.

Encoding Information in DNA

  • DNA contains an extensive, unrestricted sequence of nucleotides, allowing it to encode an infinite amount of information.
  • The combination of bases (adenine, thymine, cytosine, guanine) results in vast genetic diversity.

Griffith and Avery's Experiments

  • Griffith's Experiment (1920s):
    • Showed bacterial transformation, indicating that genes can transfer from one organism to another (hereditary implications).
  • Avery's Experiment (1940s):
    • Discovered that DNA mediates bacterial transformation by utilizing hydrolytic enzymes.
    • Specifically, nuclease disrupted transformation, providing evidence that DNA is responsible for heredity.

Watson and Crick's Discovery

  • The pivotal experimental result for figuring out DNA’s structure was the X-ray diffraction image by Franklin & Wilkins in the 1950s.
  • DNA Structure:
    • Double helix formed by two strands of nucleotides held together by hydrogen bonds.
    • Base pairs consist of adenine with thymine (A-T) and cytosine with guanine (C-G).

DNA Replication Process

  • Requirements: DNA replication requires:
    • A template strand
    • Free nucleotides
    • DNA polymerase enzyme
    • ATP and other enzymes
  • Semiconservative Process:
    • Each new DNA molecule consists of one parental strand and one newly synthesized strand.
    • This aligns with Watson and Crick's model, ensuring that both strands are retained during replication.

Gene Categories

  • Three Basic Categories of Genes:
    1. Structural Genes: Directly encode proteins (enzymes).
    2. Regulatory Genes: Encode proteins that regulate the expression of other genes (act as switches).
    3. Operator Genes: DNA sequences that serve as binding sites for regulatory proteins, controlling transcription initiation.

Antiparallel Nature & Base Pairing

  • Strands of DNA run in opposite directions (antiparallel) which stabilizes the double helix.
  • Specific base pairing (A-T and C-G) due to molecular shape ensures accurate replication and minimizes mutations.

Generation Time in Bacteria

  • Generation Time: The time it takes for a bacterial cell to divide.
    • Faster replication is necessary before binary fission, which is influenced by environmental conditions and mutation frequencies.

Chromosome vs. Plasmid DNA

  • Chromosomes: 46 segments or 23 pairs in humans; larger in size and contain the main genome.
  • Plasmids: Small, extrachromosomal DNA, capable of independent replication in bacteria, often used in genetic engineering.