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Energy and Carbon Acquisition in Organisms: An Overview of Nutritional Strategies

This text explores the various nutritional strategies organisms use to obtain energy and carbon for synthesizing organic compounds. It delves into the diversity of energy sources in prokaryotes, including phototrophs that use light and chemotrophs that utilize inorganic chemicals. The distinctions between autotrophs (self-feeders) and heterotrophs (other-feeders) are examined, along with specific examples like cyanobacteria. Furthermore, it highlights the evolution of life and the role of cyanobacteria in shaping Earth's oxygen-rich atmosphere.

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Energy and Carbon Acquisition in Organisms: An Overview of Nutritional Strategies

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  1. Nutrition • how organisms obtain energy and carbon to make organic compounds • diverse in prokaryotes

  2. Energy Sources • Light • phototrophs • Inorganic chemicals (eg. H2S, NH3, Fe2+) • chemotrophs • Organic compounds • chemotrophs

  3. Carbon Sources • CO2 • autotroph (self feeder) • Organic Compounds • heterotroph (other feeder)

  4. Photoautotrophs • energy from light • carbon from CO2 • most plants, some protists • most photosynthetic prokaryotes

  5. example • cyanobacteria • H2O + CO2 with light • releases oxygen

  6. another example • Purple sulfur bacteria • H2S + CO2 with light • releases sulfur • also green sulfur bacteria • light from hydrothermal vents!

  7. Chemoautotrophs • energy from inorganic chemicals • carbon from CO2 • only certain prokaryotes

  8. symbiosis • 2 kinds of organisms live in direct contact • symbiont is smaller one (vs host)

  9. example • tube worm symbionts • live inside tube worms • Use H2S, CO2 gathered by host. • Make food for both.

  10. Photoheterotrophs • energy from light • carbon from organic compounds • certain prokaryotes

  11. example • purple nonsulfur bacteria • accessory pigments—absorb diff.  • bacteriochl a • blue • carotenoids • yellow, red

  12. Chemoheterotrophs • energy and carbon from organic compounds • most prokaryotes and protists, fungi, animals, some plants

  13. example • lactic acid bacteria • including Lactobacillus • yogurt • requires many nutrients • human gut, vagina • “probiotics”?

  14. History of Early Life • 4.5 bya the Earth formed conditions extreme • 100 °C, CH4, CO2, H2S, Fe2+, N2, NH3 • 3.5 bya first fossil evidence of life: complex cyanobacteria • 3.2 bya fossils from hydrothermal vent community

  15. stromatolite: fossil colony of cyanobacteria Ancient cyanobacteria look like modern ones Knoll, A.H. (2003) Life on a Young Planet: The First Three Billion Years of Evolution on Earth. Princeton University Press, Princeton, New Jersey. (Milner Library, 5th floor)

  16. Cyanobacteria produced O2 Atmosphere • H2O + CO2 (w/light) ---> glucose + O2 • O2 precipitates iron (sea & land) before accumulates • 2.5 bya banded iron formations • 2 bya O2 accumulates in atmosphere • O2 is pollutant-breaks chemical bonds

  17. oxygen and metabolism • obligate aerobes require O2 • obligate anaerobes killed by O2 • facultative anaerobes OK either way

  18. some prokaryotes survived: • 1) anaerobic habitats (no O2) • 2) evolved antioxidant mechanisms • 3) used O2 as electron receptor • major innovation • aerobic resp evolved • more complex life forms possible

  19. some prokaryotes can fix nitrogen • N N is N2 in air • enzyme nitrogenase • N2-->NH3 (ammonia)

  20. examples: symbiotic nitrogen fixers • 1) Rhizobium • root nodules of legumes (eg soybeans) • N for plant and field • 2) Anabaena (cyanobacterium) • in water fern Azolla • rice fields

  21. nitrogen fixation & oxygen • O2 poisons nitrogenase • cyanobacterial strategies: • 1) avoid oxygen • 2) PS & N-fix diff places or times • 3) special N-fix cells—heterocytes • formerly heterocysts

  22. summary • diverse biochemistry • create and adapt to environment • put together & take apart almost all molecules of modern life • cyanobacteria most self-sufficient: need light, CO2, N2, H2O, minerals

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