RNA World

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  1. Miller-Urey experiment
    • Showed that mimicking prebiotic conditions in the lab could result in the production of the 20 most common amino acids.
    • Proteins were originally thought to be the heritable information.
  2. Peptide Nucleic Acid
    • Possibly pre-RNA
    • Similar to RNA
    • Can be generated under ‘prebiotic conditions’
  3. RNA
    • Woese/Crick/Orgel proposed that RNA could catalyze reactions.
    • RNAs can self-replicate, cut and elongate oligonucleotides
    • present in many of the oldest (slowest evolving) and critical cellular processes
    • transcription and translation, cofactors
    • Can store and transmit information (and is subject to natural selection)
    • High local concentrations speed assembly
    • RNAs can polymerize in the presence of clay (montmorillonite)
  4. Why RNA -> DNA?
    • DNA allows for specialization in cells, DNA could store genetic info while RNA could be a cell messenger.
    • DNA is more stable than RNA
    • due to the deoxyribose sugar is less reactive
    • double-strandedness (ds) shields information from unwanted interactions
    • DNA replication has proof
    • reading systems lacking in RNA replication
    • ds also provides an inherent error-correction
    • Higher stability = lower mutation rates = high fidelity = longer genes and genomes
    • More information and more complexity
  5. Virulence factors
    • Secretion systems
    • Adhesins-proteins that recognize and bind specific substrates
    • Motility-flagella, fimbrae (get where you need and attach) 
    • Toxins-endo/LPS, ecto
    • Cellulases
    • Collagenases
    • antibiotic resistance
  6. Coincidental Evolution
    Virulence is not directly selected for, it's a by-product of selection on other traits.
  7. Short sighted evolution
    • A pathogen will experience many generations within a host that makes it well-adapted to its host before it can be transmitted.
    • Traits for growth at the cost of transmissibility may rise to high frequency.
  8. Trade-off hypothesis
    • Pathogenicity and transmissibility shape the alleles that rise to high frequency.
    • Disease transmitted by physical contact have a reduced fitness.
  9. Facultative symbiosis
    Mutualisms are not important to the survival of either species, but engage in mutualism while the other species is around.
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RNA World
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