Urea Formation in Liver from Excess Amino Acids

• We can’t store excess amino acid (over daily need for protein synthesis) in our body, as the amino groups make them potentially toxic, so they’re deaminated in hepatocytes
• The reaction is an oxidation reaction producing ammonia and organic acid can enter Krebs cycle in aerobic respiration; it is soluble and toxic (raises cell pH)

  A) NH_2

  B) COOH

  C) H

  D) C

  E) R

  F) amino acid

  
• Ammonia binds to CO_2, forming urea via ornithine cycle, ATP needed for urea synthesis; NH_3 + CO_2 → CO(NH_2)_2 + H_2O - urea is soluble but less toxic; goes to liver via hepatic vein into vena cava, then to kidneys via renal arteries and filtered out of blood plasma, excreted in urine

  A) Ornithine

  B) Citrulline

  C) Arginine

  D) Ammonia

  E) NH_3

  F) CO_2

  G) H_2O

  H) NH_3

  I) H_2O

  J) H_2O

  K) Urea

  L) CO(NH_2)_2

  
• Other nitrogenous waste, uric acid, is far less toxic than urea, soluble, and requires little water needed for excretion, so in organisms where water conservation is key (birds, reptiles, insects)