Amino Acid & Protein Metabolism

Topics in this chapter

• Amino Acid Nitrogen Metabolism
• Urea Cycle and Ammonia Handling
• Amino Acid Catabolism and Energy
• Methionine and One-Carbon Metabolism
• Aromatic Amino Acid and Neurotransmitter Metabolism
• Amino Acid Transport and Excretion
• Inherited Amino Acid Disorders

Practice questions

1. Question 1Q-E4F6B3

   A 7-day-old neonate presents with poor feeding, vomiting, and a maple syrup-like odor to the urine. Laboratory evaluation reveals severe metabolic ketoacidosis. Which of the following enzyme deficiencies is responsible for this condition?

   1. A.Phenylalanine hydroxylase
   2. B.Branched-chain alpha-keto acid dehydrogenase complex
   3. C.Homogentisate 1,2-dioxygenase
   4. D.Cystathionine beta-synthase
   See the answer and solution
2. Question 2Q-A64A71

   A 45-year-old man comes to the physician because of progressive fatigue, joint pain, and bluish-black discoloration of his sclerae and ear cartilage. His urine turns dark upon standing when exposed to air. This patient's condition is most likely caused by a deficiency of which of the following enzymes?

   1. A.Tyrosinase
   2. B.Homogentisate 1,2-dioxygenase
   3. C.Fumarylacetoacetate hydrolase
   4. D.Alpha-keto acid dehydrogenase
   See the answer and solution
3. Question 3Q-68CE79

   During the urea cycle, which of the following molecules acts as an essential allosteric activator of carbamoyl phosphate synthetase I (CPS I)?

   1. A.Ornithine
   2. B.Citrulline
   3. C.N-Acetylglutamate
   4. D.Argininosuccinate
   See the answer and solution
4. Question 4Q-E59F0F

   A 6-year-old boy is brought to the clinic for evaluation of tall stature, long slender fingers (arachnodactyly), downward lens dislocation (ectopia lentis), and a history of thromboembolic events. Laboratory tests show elevated plasma homocysteine and methionine levels. This condition is most commonly due to a defect in which of the following enzymes?

   1. A.Methionine synthase
   2. B.Cystathionine beta-synthase
   3. C.Methylmalonyl-CoA mutase
   4. D.Cystathionase
   See the answer and solution
5. Question 5Q-91752B

   Which of the following amino acids is strictly ketogenic and cannot serve as a substrate for net hepatic gluconeogenesis?

   1. A.Alanine
   2. B.Aspartate
   3. C.Leucine
   4. D.Valine
   See the answer and solution