Block 10 Amino Acid Metabolism

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| By Chachelly
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Block 10 Amino Acid Metabolism - Quiz

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Questions and Answers
  • 1. 

    Which of the following amino acids is both essential and glucogenic?

    • A.

      Alanine (Ala, A)

    • B.

      Methionine (Met, M)

    • C.

      Leucine (Leu, L)

    • D.

      Proline (Pro, P)

    • E.

      Lysine (Lys, K)

    Correct Answer
    B. Methionine (Met, M)
    Explanation
    Methionine is both an essential and glucogenic amino acid. Essential amino acids cannot be synthesized by the body and must be obtained through the diet. Glucogenic amino acids can be converted into glucose through various metabolic pathways. Methionine is essential because it is required for the synthesis of proteins and other important molecules in the body. It is also glucogenic because it can be converted into intermediates that can enter the glucose synthesis pathway, providing a source of glucose when needed.

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  • 2. 

    K.L. was born in Ville de Saguenay (Quebec), birth was uneventful. However, she failed to thrive. Suddenly at the age of 5 months her condition deteriorated rapidly and she was transferred to an emergency room. Glutamic:pyruvic transaminase (GPT), aspartate aminotransferase (AST), ammonia and creatinine levels in blood were elevated; attending physicians noticed a strong cabbage-like smell originating from her. The most likely diagnosis is

    • A.

      Tyrosinemia I

    • B.

      Hyperlysinemia

    • C.

      Cystinuria

    • D.

      Methylmalonic aciduria

    • E.

      Glycine cleavage enzyme deficiency

    Correct Answer
    A. Tyrosinemia I
    Explanation
    The correct answer is Tyrosinemia I. This is because the patient's symptoms and laboratory findings are consistent with this condition. Elevated levels of GPT, AST, ammonia, and creatinine in the blood are indicative of liver dysfunction, which is a characteristic feature of Tyrosinemia I. Additionally, the presence of a strong cabbage-like smell suggests the accumulation of tyrosine metabolites in the body, which is a characteristic finding in this disorder.

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  • 3. 

    The presence of phenylpyruvate and phenylketones in a child’s blood are indications of the genetic disorder Phenylketonuria.  How does this compound accumulate?  This is a disorder of phenyalanine metabolism which results from:

    • A.

      Too little product formation of a metabolic pathway

    • B.

      Too much substrate accumulation for an enzymatic reaction

    • C.

      An undersupply of tyrosine for protein translation

    • D.

      An oversupply of homogentisic acid

    • E.

      Modification of blood proteins by metabolic acids

    Correct Answer
    B. Too much substrate accumulation for an enzymatic reaction
    Explanation
    Phenylketonuria is a genetic disorder that affects the metabolism of phenylalanine. In individuals with this disorder, there is a deficiency of the enzyme phenylalanine hydroxylase, which is responsible for converting phenylalanine into tyrosine. As a result, phenylalanine accumulates in the body, leading to the production of phenylpyruvate and phenylketones. These compounds are indicators of the excessive accumulation of phenylalanine, causing the metabolic pathway to have an excess of substrate for the enzymatic reaction. Therefore, the correct answer is "too much substrate accumulation for an enzymatic reaction."

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  • 4. 

    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

    Correct Answer
    C. Phenylalanine
    Explanation
    Coconut protein is considered biologically inferior because it lacks several essential amino acids. Phenylalanine is one of these essential amino acids that is missing in coconut protein. Therefore, to enhance the biological value of transgenic coconuts' protein, it is crucial to ensure that it contains an adequate amount of phenylalanine.

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  • 5. 

    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

    Correct Answer
    B. Cystathionine synthase
    Explanation
    A deficiency of cystathionine synthase would result in high blood levels of homocysteine (and also methionine). Cystathionine synthase is an enzyme that plays a crucial role in the methionine metabolism pathway. It converts homocysteine to cystathionine, which is further metabolized to produce cysteine. If cystathionine synthase is deficient, homocysteine cannot be converted to cystathionine, leading to its accumulation in the blood. This can increase the risk of atherosclerosis, as high levels of homocysteine have been associated with damage to blood vessels and the development of plaque.

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  • 6. 

    . A negative nitrogen balance is most likely 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

    Correct Answer
    C. A political prisoner who went on a hunger strike
    Explanation
    A negative nitrogen balance occurs when the body is breaking down more protein than it is synthesizing. In this case, a political prisoner who went on a hunger strike would most likely experience a negative nitrogen balance because they are not consuming enough protein or calories to meet their body's needs. Without an adequate intake of protein, the body will start breaking down muscle tissue to obtain the necessary amino acids, leading to a negative nitrogen balance.

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  • 7. 

    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 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

    Correct Answer
    A. Arginase
    Explanation
    The correct answer is Arginase. This is because the patient's symptoms, such as vomiting, lethargy, and convulsions, along with laboratory findings of hyperammonemia and elevated levels of glutamine, citrulline, and arginine, suggest a urea cycle disorder. Arginase is the enzyme responsible for the final step of the urea cycle, converting arginine to ornithine and urea. Deficiency in arginase leads to the accumulation of arginine and subsequent elevation of citrulline and glutamine, resulting in hyperammonemia.

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  • 8. 

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

    • A.

      Ornithine transcarbamoylase deficiency

    • B.

      Long-chain acyl-CoA dehydrogenase deficiency

    • C.

      . Methylmalonic acidemia

    • D.

      Vitamin B12 deficiency

    • E.

      Maple syrup urine disease

    Correct Answer
    E. Maple syrup urine disease
    Explanation
    In Maple syrup urine disease (MSUD), there is a deficiency of the branched-chain alpha-ketoacid dehydrogenase enzyme complex, leading to the accumulation of leucine, isoleucine, and valine. This results in the characteristic sweet-smelling urine (maple syrup odor) and neurological symptoms such as encephalopathy. Hypoglycemia and ketonuria are also commonly seen in MSUD. The normal plasma ammonia level helps to differentiate MSUD from other urea cycle disorders, such as ornithine transcarbamoylase deficiency. Long-chain acyl-CoA dehydrogenase deficiency and methylmalonic acidemia would not typically present with elevated levels of leucine, isoleucine, and valine. Vitamin B12 deficiency would not cause the specific pattern of amino acid elevation seen in MSUD.

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  • 9. 

    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

    Correct Answer
    A. Metabolism of branched-chain amino acids
    Explanation
    The correct answer is metabolism of branched-chain amino acids. Maple syrup urine disease (MSUD) is a genetic disorder that affects the metabolism of branched-chain amino acids (leucine, isoleucine, and valine). In individuals with MSUD, there is a deficiency of an enzyme complex that is responsible for breaking down these amino acids. As a result, these amino acids and their byproducts accumulate in the body, leading to the characteristic odor of maple syrup in the urine. Defects in the metabolism of aromatic or sulfur-containing amino acids, transformation of carbohydrates to amino acids, or one-carbon transfer reactions would not result in this specific symptom.

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  • 10. 

    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

    Correct Answer
    E. Phenylalanine
    Explanation
    Dihydrobiopterin reductase is an enzyme involved in the synthesis of tetrahydrobiopterin (BH4), which is a cofactor for the enzyme phenylalanine hydroxylase. Phenylalanine hydroxylase converts phenylalanine to tyrosine. Therefore, a deficiency of dihydrobiopterin reductase would lead to decreased levels of BH4, resulting in impaired phenylalanine metabolism and increased blood levels of phenylalanine.

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  • 11. 

    A.B. is transferred into the emergency room of a local hospital. Upon investigation high levels of glutamate:oxaloacetate transaminase (GOT) and glutamate:pyruvate transaminase (GPT) are found in his serum. His problems probably involve the following organ:

    • A.

      Heart

    • B.

      Brain

    • C.

      Liver

    • D.

      Muscle

    • E.

      Lungs

    Correct Answer
    C. Liver
    Explanation
    The presence of high levels of glutamate:oxaloacetate transaminase (GOT) and glutamate:pyruvate transaminase (GPT) in A.B.'s serum suggests liver involvement. These enzymes are primarily found in the liver and their elevated levels indicate liver damage or dysfunction. The other organs listed (heart, brain, muscle, lungs) do not typically produce significant amounts of these enzymes, making the liver the most likely organ affected in this case.

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  • 12. 

    The figure shows the metabolism of an anti-hypertensive drug in 258 unrelated British volunteers. Which statement about this experiment is false?

    • A.

      Patients in group A would get the lowest reduction of blood pressure from a given dose

    • B.

      Patients in group C would be most at risk of getting an overdose

    • C.

      The drug is converted by a cytochrome P450

    • D.

      Patients in the left of the diagram metabolize the drug only very slowly.

    Correct Answer
    D. Patients in the left of the diagram metabolize the drug only very slowly.
    Explanation
    The statement "Patients in the left of the diagram metabolize the drug only very slowly" is false. This is because the figure shows that patients in the left of the diagram metabolize the drug at a faster rate compared to patients on the right.

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  • Current Version
  • Mar 22, 2023
    Quiz Edited by
    ProProfs Editorial Team
  • Jun 18, 2012
    Quiz Created by
    Chachelly
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