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Genetics Key Concepts: Gene Function, Transcription, and Regulation

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  • Beadle and Tatum experiment hypothesis
    Genes control biochemical reactions by encoding enzymes that catalyze specific metabolic steps.
  • Beadle and Tatum experiment method
    Irradiated Neurospora to create mutants, grew them on complete medium, then tested growth on minimal medium with supplements.
  • Beadle and Tatum experiment conclusion
    Each gene mutation knocks out one enzymatic step in a metabolic pathway, supporting the one gene–one enzyme hypothesis.
  • Arginine auxotroph analysis implication
    Different mutants rescued by ornithine, citrulline, or arginine show each gene corresponds to one enzyme in the pathway.
  • One gene–one polypeptide chain hypothesis
    Each gene encodes one polypeptide chain; proteins may have multiple polypeptides, unlike the older one gene–one protein idea.
  • Using supplements to map biochemical pathway blocks
    If mutant grows with downstream supplements but not upstream, the block is before the earliest rescuing compound.
  • Structure of a typical prokaryotic gene
    Includes promoter, transcription start site (+1), uninterrupted coding region, and terminator.
  • Collinearity in prokaryotic genes
    The order of codons in DNA matches the order of amino acids in the protein via mRNA.
  • Open reading frame (ORF)
    A continuous stretch of codons from a start codon to an in-frame stop codon without internal stops.
  • Role of RNA polymerase in prokaryotic transcription
    Catalyzes RNA synthesis by forming phosphodiester bonds using DNA as a template.
  • Role of sigma factor in prokaryotic transcription
    Helps RNA polymerase recognize promoters and initiate transcription at the correct site.
  • Steps of prokaryotic transcription initiation
    RNA polymerase holoenzyme binds promoter → DNA unwinds → first bonds form → promoter escape and sigma release.
  • Prokaryotic transcription elongation
    RNA polymerase moves 3’→5’ on template strand, synthesizing RNA 5’→3’.
  • Prokaryotic transcription termination types
    Rho-independent (hairpin + U-tract) and rho-dependent (Rho helicase dislodges polymerase).
  • Effect of promoter mutations in prokaryotes
    Mutations in -10/-35 regions often reduce or abolish transcription initiation.
  • Differences in RNA polymerases between prokaryotes and eukaryotes
    Eukaryotes have multiple RNA polymerases (I, II, III) for different RNA types; prokaryotes have one.
  • Differences in gene structure: prokaryotes vs eukaryotes
    Eukaryotic genes have complex promoters and introns; prokaryotic genes usually lack introns.
  • Eukaryotic transcription initiation complexity
    Requires multiple general transcription factors and complex promoter elements.
  • Posttranscriptional modifications in eukaryotes
    5’ capping, 3’ poly-A tail, and splicing of introns to produce mature mRNA.
  • Function of 5’ cap in eukaryotic mRNA
    Protects mRNA, aids ribosome binding, and facilitates nuclear export.
  • Function of 3’ poly-A tail
    Increases mRNA stability and assists in export and translation.
  • Role of introns in eukaryotic genes
    Enable alternative splicing, contain regulatory elements, and facilitate exon shuffling.
  • Impact of splice-site mutations
    Can cause exon skipping or intron retention, often leading to frameshifts or premature stops.
  • Impact of promoter/enhancer mutations in eukaryotes
    Reduce transcription by impairing RNA polymerase II or general transcription factor binding.
  • Coupling of transcription and translation
    Occurs in prokaryotes but not in eukaryotes due to nuclear compartmentalization.