Microbiology 330

DNA Structure and Function

  • Supercoiling is vital for DNA: condenses for fitting in the cell.

Genetic Elements

  • Genes for essential processes are found on:

    • Chromosomes and plasmids.

  • Chromosomes encode essential genes; plasmids encode non-essential genes.

DNA Replication

  • Essential Enzyme: DNA helicase unwinds DNA, forming a replication fork.

  • RNA Primers: Synthesized by primase to start DNA elongation.

Polymerase Chain Reaction (PCR)

  • PCR uses heat to denature DNA, replacing the function of DNA helicase.

  • PCR steps:

    • Denaturing: Mix heated to separate strands.

    • Annealing: Cool to allow primers to bind.

    • Extension: Heated to 72ºC for DNA polymerase binding.

  • Specificity in PCR is determined by primers.

Transcription Process

  • Promoters are DNA sequences recognized by RNA polymerase.

  • RNA polymerase unwinds DNA, creating a transcription bubble.

  • Archaea RNA polymerase is more similar to eukaryotic than bacterial.

Translation

  • tRNA transfers correct amino acids to the ribosome.

  • Codon on mRNA matches with tRNA anticodon.

  • Translation is terminated by release factors at stop codons.

Regulation of Gene Expression

  • Mutations upstream of the start codon can alter protein production while keeping mRNA levels constant, indicating roles of promoter and ribosome-binding site.

Quorum Sensing

  • Mechanism for bacteria to assess population density using autoinducers.

  • Bioluminescence in Aliivibrio fischeri peaks during late log to early stationary phase.

Protein Structure

  • Codon on mRNA: triplet of bases.

  • Protein Structure Types:

    • Secondary: α-helices and β-sheets formed by hydrogen bonds.

    • Tertiary: stabilized by hydrophobic interactions and disulfide bonds.

    • Molecular chaperones aid in protein folding.