BIOL 201 - Lecture 3

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BIOL 201 - Lecture 3
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2011-09-21 15:04:46
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Lecture 3
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  1. Why Study Prokaryotes?
    • Earliest form of life
    • Diverse, abundant and ubiquitous
    • Relatively simple organisms for various biological studies
    • Essential to biosphere functioning (biogeochemistry)
    • Industrial potential
    • Importance to humans (Digestion Diseases Environment)
  2. Biological characteristics of Prokaryotes
    • Most are unicellular and small (0.05-1 micron in width)
    • Most have rigid cell walls
    • DNA – One double-stranded circular chromosome (plus plasmids of same form)
    • Lack nucleus
    • Lack other membrane-bound organelles (except photosynthesisers)
    • Lack cytoskeleton Smaller ribosomes than eukaryotes (70S vs 80S)
    • No sexual reproduction
    • Simple flagella common
    • Classified by size, shape, cellular arrangement, nutrition
  3. What are the implications of being microscopically small?
    • • Intimate contact with environment…For microbes, ”Everything is everywhere, and the environment selects”
    • • Rapid reproduction
    • • High ‘rate of living’– Metabolic rate is generally proportional to (volume)1/4
    • • Ecology of prokaryotes defined by aquatic continuum
    • – Almost always associated with water
    • • Direct metabolic demand
    • • Supplies nutrients
    • • Removes wastes
    • – Small size means water is extremely viscous
    • • Most movement is passive in water flow
    • • Some can swim but usually just a few mm.
    • - Restricted mobility implies spatial and temporal heterogeneity in nutrients and environment critical to activity
    • Scale: “The prokaryotic world is a mosaic of tiny islands of discontinuous resources” (B. Dyer)…and therefore of activity hotspots.
  4. Nutrient acquisition from the environment
    • Rigid cell wall precludes phagocytosis
    • Uptake across cell membrane restricted to small organics and inorganics
    • – Extracellular hydrolysis of larger organics critical
    • – Enzymes constantly being secreted into extracellular matrix
    • – Diffusion of materials in solution toward cell critical
    • Many have resource storage capacity as granules or inclusion bodies
    • – Carbon: Glycogen, butyric acid; Phosphorus and Nitrogen (‘PP’ and ‘C’ in cyanobacterium in figure); Sulfur
    • .– Gas vacuoles for buoyancy in photosynthetic groups
  5. Fundamentals of energetics and nutrition
    • Metabolism = energy transfer = oxidation/reduction
    • • Nutrients (Carbon etc.)
    • • Waste removal
  6. ´╗┐Prokaryotic energy groupings completed
  7. Prokaryotic Reproduction= Fission
    • 1) Duplication of circular chromosome
    • 2) Cell elongation
    • 3) Ingrowth of plasma membrane and attachment of DNA
    • 4) Ingrowth of cell wall
  8. Prokaryotic cell growth: Patterns and Controls
    • 1- lag phase
    • 2- exponential phase
    • 3- stationary phase
    • 4- death phase
    • Environmental controls: Water, availability, pH, Temperature, Oxygen, Nutrients
    • Biological controls within communities: Dispersal, competition, inhibition
  9. Mechanisms driving genetic variability
    • Mutation plus rapid generation time
    • - Chromosome duplication mutation rate during fission
    • ~1 mutation in a gene per 10 million cell divisions
    • E. coli: 1,000,000,000 cells cultured in 10 h-> ~100 cells with mutations in a particular gene of interest
    • Genetic transfers (unidirectional gene flow)
    • – Conjugation (plasmids donated)
    • – Transformation (DNA in environment taken up)
    • – Transduction (bacteriophages)

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