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Anaerobic Respiration, Metabolism Evolution

cellular respiration of protein - 1st broken down into amino acids 

  • deamination - process that removes the amino group
  • reactions convert remaining carbon chain into parts that take place in glycolysis/Krebs cycle
  • alanine converted to pyruvate
  • glutamate converted into a-ketoglutarate
  • aspartate converted into oxaloacetate

cellular respiration of fat - 1st broken down into fatty acids and glycerol 

  • beta oxidation - process that removes 2-carbon acetyl groups from fatty acids to convert them into acetyl groups
    • takes place in mitochondrial matrix
    • each acetyl group combines w/ coenzyme A to form acetyl-CoA
  • produces 20% more ATP than glucose per 6-carbon molecule
  • contains 2x as much kilocalories per gram

fermentation - process that recycles NAD+ in absence of oxygen 

  • uses organic compound as electron acceptor instead of oxygen

ethanol fermentation - occurs in yeast (single-celled fungi) 

  • pyruvate accepts hydrogen from NADH
  • enzymes remove CO2 from pyruvate through decarboxylation, making acetaldehyde (2-carbon molecule)
  • CO2 released causes bread to rise
  • acetaldehyde + NADH >> ethanol + NAD+
  • ethanol begins to kill yeast at 12% concentration

lactic acid fermentation - uses lactate dehydrogenase to transfer H from NADH to pyruvate  

  • pyruvate + NADH >> lactic acid + NAD+
  • lactate - ionized form of lactic acid
  • interferes w/ muscle function when circulating blood can't remove lactic acid fast enough

evolution of metabolism - changed stage by stage 

  • degradation - breaks down organic molecules abiotically produced
    • started w/ origin of ability to use chemical bond energy
  • glycolysis - initial breakdown of glucose
    • captures a larger amount of chemical bond energy by breaking bonds in steps
    • hasn't changed in over 2 billion years
  • anaerobic photosynthesis - uses light to pump protons from cells
    • still uses chemiosmosis to produce ATP
    • evolved in absence of oxygen
    • dissolved H2S provided hydrogen for procedure
  • oxygen-forming photosynthesis - H2O replaced H2S
    • generates oxygen instead of sulfur
    • all oxygen in atmosphere from oxygen-forming photosynthetic reaction
  • nitrogen fixation - obtaining nitrogen atoms from N2 gas by breaking triple bonds
    • evolved in hydrogen rich atmosphere
    • occurs in oxygen-free environments (oxygen poisons nitrogen-fixation)
  • aerobic respiration - final event in history of metabolic evolution
    • gets energy from electrons in organic molecules
    • uses same proton pumps as photosynthesis
    • 1st evolved among purple nonsulfur bacteria (obtained hydrogen from organic molecules)
    • mitochondria thought to be descendents of nonsulfur bacteria
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