Deck 26: Amino Acid Metabolism

Question 1

Quantitatively, the major metabolic fate of glycine in the body is:

A)Conversion to serine by addition of a one-carbon unit from tetrahydrofolate.
B)Transamination and oxidation to oxalic acid.
C)Cleavage to carbon dioxide, ammonia, and a one-carbon group on tetrahydrofolate.
D)Use for heme biosynthesis by d-aminolevulinate synthetase.
E)Use for the synthesis of pyrimidine nucleotides.

Answer 1

Cleavage to carbon dioxide, ammonia, and a one-carbon group on tetrahydrofolate.

Question 2

A 2-week-old infant presents with vomiting, lethargy, and convulsions without evidence of an infectious process.Laboratory examination reveals hyperammonemia with alkalosis.Glutamine, citrulline, and arginine levels are found elevated in the blood.The enzyme that is most likely deficient in this patient is:

A)Arginase.
B)Carbamoyl-phosphate synthetase I.
C)Arginosuccinate lyase.
D)Ornithine transcarbamoylase.
E)Arginosuccinate synthetase.

Answer 2

Arginase.

Question 3

A 2-week-old infant presents with vomiting, lethargy, and convulsions without evidence of an infectious process.Laboratory examination reveals hyperammonemia without acidosis.The diagnosis is a hereditary deficiency of N-acetylglutamate synthetase.N-acetylglutamate is an allosteric activator of:

A)Arginase.
B)Carbamoyl-phosphate synthetase I.
C)Arginosuccinate lyase.
D)Ornithine transcarbamoylase.
E)Arginosuccinate synthetase.

Answer 3

Carbamoyl-phosphate synthetase I.

Question 4

A nurse notices that the urine produced by a newborn infant has the odor of maple syrup.Which of the following pathways is most likely defective?

A)Metabolism of branched-chain amino acids.
B)Metabolism of aromatic amino acids.
C)Metabolism of sulfur-containing amino acids.
D)Transformation of carbohydrates to amino acids.
E)One-carbon transfer reactions.

Question 5

A newborn with acute encephalopathy is found to have hypoglycemia and ketonuria.Plasma leucine, isoleucine, and valine levels are markedly elevated, but the plasma ammonia level is normal.This is most likely a case of:

A)Ornithine transcarbamoylase deficiency.
B)Long-chain acyl-coenzyme A (CoA) dehydrogenase deficiency.
C)Methylmalonic acidemia.
D)Vitamin B12 deficiency.
E)Maple syrup urine disease.

Question 6

A negative nitrogen balance is most likely to be present in:

A)A heavyweight boxer training for the world championship.
B)A fast-growing teenager who eats 3500 calories of junk food every day.
C)A political prisoner who went on a hunger strike.
D)A woman who is 8 months pregnant.
E)A patient who is recovering from successful cancer surgery and chemotherapy.

Question 7

A 1-year-old child with mental retardation has a deficiency of dihydrobiopterin reductase.This enzyme deficiency leads to an increased blood level of:

A)Tyrosine.
B)Methionine.
C)Glucocerebroside.
D)Glycine.
E)Phenylalanine.

Question 8

Coconut protein is biologically inferior because it is lacking many essential amino acids.In your efforts to make transgenic coconuts with protein of high biological value, you should definitely ensure that your coconut protein has an adequate amount of:

A)Glutamine.
B)Arginine.
C)Phenylalanine.
D)Tyrosine.
E)Serine.

Question 9

The nitrogen balance is likely to be positive:

A)In a professional boxer who retired from boxing and daily training 2 months ago.
B)In a patient with arthritis who has recently been prescribed high doses of cortisol.
C)In a person living on a diet that is deficient in methionine but otherwise contains enough protein.
D)Three days after the last meal.
E)During recovery from a severe infectious illness.

Question 10

High homocysteine levels are associated with an increased risk of atherosclerosis.A deficiency of which of the following enzymes would result in high blood levels of homocysteine (and also methionine)?

A)Tyrosine hydroxylase.
B)Cystathionine synthase.
C)Threonine dehydratase.
D)Glutathione reductase.
E)L-Amino acid oxidase.