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