Chemical Reactions In The Body

• Building reactions: Anabolism - requires energy
• Breakdown reactions: Catabolism - releases energy
• Transfer of energy in reactions:
  - coupled reactions: energy is released from one compound and used to create a bond in the formation of another compound
  - ATP (adenosine triphosphate): high-energy compound containing three phosphate groups, adenine, and ribose

note: CoA = Coenzyme A, derived from the B vitamin pantothenic acid for energy metabolism
note: aerobic: requires oxygen;  anaerobic: does not require oxygen
 

Breaking down nutrients for energy:

Glucose

• Glucose converts to pyruvate: through glycolysis: glucose is split into two 3-carbon compounds (pyruvate) in anaerobic conditions
• Pyruvate to glucose: pyruvate can, if needed, be converted back to glucose
• Pyruvate to acetyl CoA: when energy is needed in the presence of oxygen, cells remove a carbon group from pyruvate to form a 2-carbon acetyl CoA.  The stripped carbon groups are carried out of the body as carbon dioxide.  Therefore, it is an irreversible reaction.
• Acetyl CoA converts to carbon dioxide in the TCA cycle (which creates energy) or is used to make fatty acids in the body
• The Cori cycle: a path from muscle glycogen to glucose to pyruvate to lactic acid to glucose back to glycogen.  (pyruvate converts to lactic acid as a result of too little oxygen in high-intensity exercise)
   

Glycerol and Fatty Acids

• Glycerol to pyruvate: glycerol is restructured as pyruvate to form glucose or acetyl CoA
• Fatty acids to acetyl CoA: through fatty acid oxidation, fatty acids are taken apart 2 carbons at a time to combine with CoA to become acetyl CoA
• Fatty acids cannot yield glucose: 95 percent of fat cannot be converted to glucose: glycerol can yield glucose, however fatty acids cannot

Amino Acids

• Catabolism: when amino acids are needed for energy or are consumed in greater amounts than the body needs, they enter the metabolic pathways for energy: they are deaminated and converted to pyruvate, or acetyl CoA
• Amino acids to glucose: as a source of pyruvate, protein can eventually be converted to glucose
• Amino acids to fat: amino acids that are converted to actetyl CoA and not used as a fuel source are converted to fatty acids
• Deamination: stripping amino acids from their amino group results in a keto acid and ammonia
• Transamination: the transfer of an amino group from one amino acid to a keto acid
• Ammonia is converted by the liver to urea which is circulated to the kidneys and excreted (which requires additional water for excretion) in urine