bio aging ch 4.txt

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bio aging ch 4.txt
2012-10-21 19:57:46

ch 4
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  1. Alfred Russel Wallace
    Theorized that SMALLER organisms (that fragmented from larger orgs) would be FAVORED over larger organisms
  2. August Weismann
    • Somatic cells (of multicellular organisms) subject to senescence, while Germ cells are NOT
    • somatic cells went through a "wear and tear" process that germ cells were protected from
  3. Tracy SOnneborn
    Unicellular organisms who STOPPED undergoing sexual reproduction, due to constant feeding, showed senescence
  4. Wear and Tear process in somatic vs germ cells
    • 1. somatic cells have LESS nuclear DNA repair vs. germ cells
    • 2. somatic cells usually diploid (w/higher gene redundancy than haploid germ cells) so they can SUSTAIN greater amounts of unrepaired DNA damage
    • 3. somatic cells usually DIVIDE MORE SLOWLY than germ cells, so selection against damaged cells is less
  5. Thomas Kirkwood
    • Restatement of Weismann's disposable soma theory
    • Maximizing longevity is Not important evolutionary strategy
    • parental organism becomes disposable after reproduction, as evolution is only concerned with maximizing survival of OFFSPRING
  6. Peter Medawar
    • accumulation of detrimental mutations model for origin of senescence
    • NO Mechanism that natural selection plays in mortality - can't prevent or do anything related to mortality rates
  7. George Williams
    • Antagonistic pleiotropy model for origin of senescence
    • Natural selection COULD have effect on age associated mortality rates
  8. William Hamilton
    • Beneficial mutation model for origin of senescence
    • Natural selection might Favor senescent population
  9. Fecundity and longevity
    Relationship b/w reproduction and life span
  10. MacArthur and Wilson
    • 1st to include fecundity and age-specific mortality into their calculations
    • Included both Prodigal (r-selected) and prudent (k-selected) organisms
  11. Prodigal (R-selected) organisms
    • sacrificed longevity for maximum reproductive success.
    • Little parental care, many small offspring, Rapid maturation, Few reproductive episodes (one reprod. episode per life cycle = semelparous)
    • Examples:
    • Unicellular bacteria, protists and fungi
    • housefly, pacific salmon
  12. Prudent (K-selected) organisms
    • Trading reproduction for maximum longevity
    • Investment of parental care, Slow maturation, Few large offspring, multiple reproductive episodes (iteroparity)
    • Examples:
    • Redwood tree (sequoia)
    • Perennial plants (quaking aspen), large mammals (humans & whales)
  13. Robin Holliday
    • Similar data to the British aristocracy data
    • if delay sexual maturation, K selected can increase longevity
    • R selected may have to sacrifice longevity to INcrease reproduction
  14. Senescence patterns of Prokaryotes
    • Usually exhibit Type II Patterns
    • probably Type II b/c cell division rates are fast enough to replenish population when natural selection removes cells which sustained irreparable damage
    • Richard Cutler: using E coli, showed lower viability with age
    • Kapitanov & Aksenov: using A laidlawii (bacteria) also showed reduced viability with age
  15. Senescence patterns of Protists
    • Usually exhibit Type II, but also Type I can be induced
    • Amoeba: shown (by Muggleton) that on nutritionally deficient diet, progressive decline in cell division(even when nutrients replaced later), leading to extinction
    • Type A populations: one viable and one non-viable until both daughter cells non-viable
    • Type B populations: continual division until synchronous senescence occurs
    • Paramecium: (Sonneborn) can be induced to show senescence when self-fertilization prevented by constant feeding
    • Volvox carteri: multicellular (both somatic and germ cells). Somatic cells undergo synchronous senescence after 2000cell count.
  16. Senescence of Plants (multicellular org)
    • Annual plants (1yr life) and biennials (lifespans 1-3yrs): monocarps (single fruit), analogous to semelparous animals. Arabidopsis (flowering plant) and Glycine (soybean) show senescence as a result of changing light exposure times. Soybean senescence can be delayed if their flowers removed
    • Perennial plants (>3yr life): polycarps (multiple fruits), analogous to iteroparous animals. Populus (quaking aspen), bamboo (bambusoides), liveworts (no sexual stage, can live to 1mil)
  17. Unicellular fungi senescence
    S. cerevisiae (yeast): shows Gompertz pattern of senescence. One of the highest euk. mortality rates. Reproduce by budding, w/unequal distribution of mother and daughter cell
  18. Multicellular fungi senescence
    • (molds), reproduce thru hyphae, exhibit senescence depending on factors
    • Podospora anserina: reduced cell division rates as fungal grows on solid media, eventually entire colony dies when plasmids from mitochondrial introns amplified and inserted into genome in large numbers
    • Neurospora crassa: amplification of mitochondrial plasmids, and their insertion into mitochondrial genes, disrupt aerobic growth as above, leading to senescence
    • Both can be cured of senescence by inhibiting the replication of these plasmids
  19. Invertebrate animals aging patterns
    all animals capable of producing collagen, which may contribute to extracellular aging
  20. Rotifera aging
    • Invertebrate
    • age rapidly following a Type I Logistic pattern
    • Composed of post-mitotic cells (except for germ cells)
    • Lansing effect discovered using rotifers
  21. Nematoda aging
    • invertebrates
    • includes C. elegans (1st animal to have lineage of adult cell traced thru development and 1st to completely sequence)
    • Follow Type I Logistic pattern
  22. Flatworm aging
    • invertebrates
    • Charles child amputated flatworms to turn senescent ones into non-senescent ones
    • Sonneborn: also demonstrated thru amputations could regenerate (with head amputated) unlimited # of times
  23. Nemertinea (ribbonworms) aging
    • invertebrates
    • fed constant diet of nutrients will reach upper limit to body size and follow senescence
    • Can be fed and starved, in which they will exhibit Type II pattern)
  24. Drosophila melanogaster aging
    • invertebrates
    • All insects so far show type I aging patterns
    • Has fixed # of postmitotic cells as adult, which lead to Type I aging pattern
  25. Vertebrate animals and aging studies
    • Cold blooded hard to study, due to environmental factors (such as cold environment)
    • warm blooded studied most, they include Mus musculus, rat, dogs and cats, monkeys
    • General trends in mammals: longer lifespans correlate with larger body size
    • Sacher's ratio of brain-to-body weight is predictor of max lifespans in mammals, suggests metabolic rates mechanism for this