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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)
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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
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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.
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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
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Fundamentals of energetics and nutrition
 - Metabolism = energy transfer = oxidation/reduction
- • Nutrients (Carbon etc.)
- • Waste removal
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Prokaryotic energy groupings completed
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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
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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
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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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