Question 1

A 3-year-old boy develops renal failure from hyperuricemia on the second day of cytosine arabinoside therapy for acute myelogenous leukemia. Which of the following is the most likely cause of his hyperuricemia?

Accepted Answer

A)   increased catabolism of purines that are released from lysed leukemic cells
B)   inhibition of orotic acid production via the urea cycle
C)   inhibition of renal tubular transport by cytosine arabinoside
D)   inhibition of uric acid for renal excretion by ketone bodies
E)   overproduction of hypoxanthine-guanine phosphoribosyltransferase (HGPRT)  by the leukemic cellsF) None of the above
G) C) and D)

Question 2

A nucleoside analogue that is being screened as a potential anticancer agent causes gout in clinical trials. Which of the following actions of this drug may cause gout?

Accepted Answer

A)   inhibits carbamoyl phosphate synthetase
B)   inhibits the conversion of dihydrofolate to tetrahydrofolate
C)   inhibits xanthine oxidase
D)   interferes with feedback control of phosphoribosylpyrophosphate (PRPP)  synthesis
E)   interferes with feedback control of thymidylate synthaseF) A) and D)
G) A) and E)

Question 3

An enzyme system, isolated from the liver, converts deoxyuridine-5′-phosphate (dUMP)  to thymidine-5′-phosphate (dTMP) . Which of the following participates in this reaction?

Accepted Answer

A)   ATP
B)   N5,N10-methylene tetrahydrofolic acid
C)   S-adenosylmethionine
D)   thioredoxin
E)   vitamin B12F) A) and D)
G) None of the above

Question 4

A 30-year-old man comes to the ER because he has had constant severe pain in his right ankle over the past 24 hours. His uncle also had episodes of pain in single joints. The ankle is swollen and warm. Serum uric acid concentration is increased. Which of the following enzyme activities is most likely to be decreased in this patient?

Accepted Answer

A)   adenosine deaminase
B)   carbamoyl phosphate synthetase
C)   hypoxanthine guanine phosphoribosyltransferase
D)   ribonucleotide reductase
E)   thymidylate synthaseF) A) and B)
G) B) and C)

Question 5

Methotrexate is an inhibitor of which of the following enzymes?

Accepted Answer

A)   dihydrofolate reductase
B)   5-methyl-tetrahydrofolate transferase
C)   ribonucleotide reductase
D)   thymidylate synthase
E)   xanthine oxidaseF) A) and E)
G) A) and C)

Question 6

The initial reaction of the de novo synthesis pathway for pyrimidine nucleotides begins with glutamine and CO2 and is complete with the formation of uridine monophosphate. Which of the following represents the rate-limiting enzyme in this pathway?

Accepted Answer

A)   aspartate transcarbamoylase
B)   orotate monophosphate decarboxylase
C)   phosphoribosylpyrophosphate amido transferase
D)   PRPP synthetase
E)   ribonucleotide reductaseF) C) and E)
G) B) and C)

Question 7

Severe combined immunodeficiency disease (SCID)  is characterized by a complete lack of cellmediated and humoral immunity. This disorder results from a deficiency in which of the following enzymes?

Accepted Answer

A)   adenosine deaminase
B)   asparatate transcarbamoylase
C)   hypoxanthine-guanine phosphoribosyltransferase
D)   orotic acid decarboxylase
E)   purine nucleotide phosphorylaseF) B) and D)
G) B) and C) AEXPLANATION: Severe combined immunodeficiency disease (SCID) is a disorder related to defects in the activity of the purine nucleotide catabolism enzyme, adenosine deaminase (ADA)

Question 8

Allopurinol is an inhibitor of xanthine oxidase. Administration of allopurinol to a patient with gout and normal HGPRT levels would be expected to lead to which of the following?

Accepted Answer

A)   decreased levels of PRPP
B)   decreased xanthine in the blood
C)   increased de novo synthesis of IMP
D)   increased hypoxanthine in the urine
E)   increased urate in the urineF) All of the above
G) C) and D) DEXPLANATION: Most forms of gout are the result of excess purine production and consequent catabolism or due to a partial deficiency in the salvage enzyme, HGPRT. Most forms of gout can be treated by administering the antimetabolite allopurinol that strongly inhibits xanthine oxidase. The substrates for xanthine oxidase are hypoxanthine and xanthine; therefore, inhibition of the enzyme results in increased levels of hypoxanthine and xanthine in the blood and urine.

Question 9

You are treating a 4-year-old child who has been afflicted with recurrent infections. The child exhibits retarded development, weakness, and weight loss. Physical examination also shows absent tonsils and blood work reveals a lack of lymphocytes. These signs and symptoms are due to which of the following disorders?

Accepted Answer

A)   hyperuricemia
B)   Kelley-Seegmiller syndrome
C)   Lesch-Nyhan syndrome
D)   orotic aciduria
E)   severe-combined immunodeficiency (SCI
D)  F) D) and E)
G) B) and E)

Question 10

Which of the following groups of amino acids are nitrogen donors in purine ring biosynthesis?

Accepted Answer

A)   arginine, lysine, histidine
B)   asparagine, lysine, histidine
C)   glutamate, histidine, aspartate
D)   glutamine, glycine, aspartate
E)   glycine, proline, lysineF) A) and E)
G) A) and D)

Question 11

A 7-year-old boy is brought to the physician by his mother for a follow-up examination. He has had choreoathetosis, spasticity, and mental retardation since infancy and self-mutilation for 3 years. Laboratory studies show an increased serum uric acid concentration. The enzyme deficiency causing this disorder increases serum uric acid concentration by which of the following changes in purine metabolism?

Accepted Answer

A)   decreased activity of xanthine oxidase
B)   decreased formation of adenosine monophosphate
C)   decreased utilization of phosphoribosylpyrophosphate (PRPP)  in salvage
D)   increased activity of adenosine deaminase
E)   increased activity of PRPP synthetaseF) A) and B)
G) B) and C)

Question 12

The parents of a 1-year-old boy are alarmed at the increasing frequency of their child biting his lips and finger tips. In addition, on several occasions they have noticed what appears to be "orange sand" in their son's diapers. They report to their pediatrician that they believe their child is delayed in acquiring motor skills such as holding up his head and sitting unaided. Clinical tests performed on serum and urine indicate a 3-fold increase in serum uric acid and a 10-fold elevation in the urinary ratio of uric acid to creatinine. These findings are suggestive of which of the following disorders?

Accepted Answer

A)   adenosine deaminase deficiency
B)   adenylosuccinate lyase deficiency
C)   Lesch-Nyhan disease
D)   purine nucleotide phosphorylase deficiency
E)   orotic aciduriaF) A) and C)
G) A) and D)

Question 13

A 4-month-old boy is brought to the physician because of failure to thrive since birth. He is below the 5th percentile for length and at the 100th percentile for weight. Physical examination shows a doll-like face and marked hepatomegaly. After a 4-hour fast, serum studies show a decreased glucose concentration and increased concentrations of lactate, triglycerides, and uric acid. Which of the following is the most likely mechanism for the increased serum uric acid concentration in this patient?

Accepted Answer

A)   decreased hepatic amidophosphoribosyltransferase activity
B)   decreased hepatic hypoxanthine-guanine phosphoribosyltransferase activity
C)   decreased hepatic phosphoribosylpyrophosphate activity
D)   increased degradation of hepatic purine nucleotides
E)   increased degradation of hepatic pyrimidine nucleotidesF) C) and D)
G) A) and B)

Question 14

A 37-year-old man presents with tophaceous deposits within the articular cartilage, synovium, tendons, tendon sheaths, pinnae, and the soft tissue on the extensor surface of the forearms. These clinical observations suggest the patient is suffering from which of the following disorders?

Accepted Answer

A)   ADA deficiency
B)   gout
C)   Lesch-Nyhan syndrome
D)   purine nucleoside phosphorylase (PNP)  deficiency
E)   von Gierke diseaseF) D) and E)
G) C) and D)

Question 15

You are examining a 5-year-old male child who has been exhibiting a tendency to bite his lower lip to the point of bleeding as well as chewing on his fingertips. Physical examination demonstrates swollen tender joints, and blood workup indicates elevated uric acid levels. These symptoms and lab results are indicative of a deficiency in which of the following enzymes?

Accepted Answer

A)   adenosine deaminase
B)   adenosine phosphoribosyltransferase
C)   AMP deaminase
D)   hypoxanthine-guanine phosphoribosyltransferase
E)   thymidylate synthaseF) None of the above
G) All of the above

Question 16

A 6-year-old boy with moderate mental retardation is brought to the physician for a follow-up examination. He has had choreoathetoid movements since the age of 16 months. He has been biting his lips and fingers for the past 2 months. His older brother has a similar condition. Physical examination shows spasticity of the lower limbs. Laboratory studies show an increased serum uric acid concentration and an increased urinary excretion of uric acid. His increased serum uric acid concentration is most likely due to which of the following?

Accepted Answer

A)   deficient amidophosphoribosyltransferase activity
B)   deficient hypoxanthine guanine phosphoribosyltransferase activity
C)   deficient xanthine oxidase activity
D)   increased adenosine phosphoribosyltransferase activity
E)   increased adenosine deaminase activityF) B) and D)
G) B) and C)

Question 17

The gouty arthritis in patients with Lesch-Nyhan syndrome results from a genetic defect in which of the following enzymes?

Accepted Answer

A)   adenosine phosphoribosyltransferase
B)   glutathione reductase
C)   hypoxanthine guanine phosphoribosyltransferase
D)   phosphoribosylpyrophosphate amidotransferase
E)   xanthine oxidaseF) A) and C)
G) A) and B)

Question 18

A 10-year-old boy who has begun chemotherapy for acute myelogenous leukemia awakens at night with fever and severe pain in the ankles. Treatment with over-the-counter analgesics does not resolve the pain. The next morning, he has pain with urination and blood in the urine. Increased degradation of which of the following compounds most likely caused this patient's symptoms?

Accepted Answer

A)   amino acids
B)   fatty acids
C)   purines
D)   pyrimidines
E)   vitamin CF) B) and E)
G) A) and D)

Question 19

A 63-year-old woman comes to the physician for a follow-up examination. She has metastatic breast cancer treated with cyclophosphamide and fluorouracil. Thymidylate synthase, which is required for deoxynucleotide synthesis, is one target of fluorouracil. Which of the following is a substrate for thymidylate synthase?

Accepted Answer

A)   dCMP
B)   dCTP
C)   dUDP
D)   dUMP
E)   dUTPF) A) and E)
G) A) and B)

Question 20

In the synthesis of pyrimidines, which of the following molecules is a direct precursor of the pyrimidine ring?

Accepted Answer

A)   aspartate
B)   fumarate
C)   glutamate
D)   glycine
E)   5-phosphoribosyl-1-pyrophosphateF) C) and D)
G) B) and E) AEXPLANATION: Synthesis of the pyrimidines requires 1 mole of glutamine, 1 mole of ATP, and 1 mole of CO2 (which form carbamoyl phosphate) and 1 mole of aspartate. An additional mole of glutamine and ATP are required in the conversion of UTP to CTP

Exam 32: Nitrogen: Nucleotide Metabolism

A 3-year-old boy develops renal failure from hyperuricemia on the second day of cytosine arabinoside therapy for acute myelogenous leukemia. Which of the following is the most likely cause of his hyperuricemia?

Correct Answer
verified

A nucleoside analogue that is being screened as a potential anticancer agent causes gout in clinical trials. Which of the following actions of this drug may cause gout?

Correct Answer
verified

An enzyme system, isolated from the liver, converts deoxyuridine-5′-phosphate (dUMP) to thymidine-5′-phosphate (dTMP) . Which of the following participates in this reaction?

Correct Answer
verified

Correct Answer
verified

Methotrexate is an inhibitor of which of the following enzymes?

Correct Answer
verified

The initial reaction of the de novo synthesis pathway for pyrimidine nucleotides begins with glutamine and CO₂ and is complete with the formation of uridine monophosphate. Which of the following represents the rate-limiting enzyme in this pathway?

Correct Answer
verified

Severe combined immunodeficiency disease (SCID) is characterized by a complete lack of cellmediated and humoral immunity. This disorder results from a deficiency in which of the following enzymes?

Correct Answer
verified
A
EXPLANATION: Severe combined immunodeficiency disease (SCID) is a disorder related to defects in the activity of the purine nucleotide catabolism enzyme, adenosine deaminase (ADA)

Allopurinol is an inhibitor of xanthine oxidase. Administration of allopurinol to a patient with gout and normal HGPRT levels would be expected to lead to which of the following?

Correct Answer
verified

Which of the following groups of amino acids are nitrogen donors in purine ring biosynthesis?

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

A 37-year-old man presents with tophaceous deposits within the articular cartilage, synovium, tendons, tendon sheaths, pinnae, and the soft tissue on the extensor surface of the forearms. These clinical observations suggest the patient is suffering from which of the following disorders?

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

The gouty arthritis in patients with Lesch-Nyhan syndrome results from a genetic defect in which of the following enzymes?

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

In the synthesis of pyrimidines, which of the following molecules is a direct precursor of the pyrimidine ring?

Correct Answer
verified
A
EXPLANATION: Synthesis of the pyrimidines requires 1 mole of glutamine, 1 mole of ATP, and 1 mole of CO₂ (which form carbamoyl phosphate) and 1 mole of aspartate. An additional mole of glutamine and ATP are required in the conversion of UTP to CTP

Exam 32: Nitrogen: Nucleotide Metabolism

A 3-year-old boy develops renal failure from hyperuricemia on the second day of cytosine arabinoside therapy for acute myelogenous leukemia. Which of the following is the most likely cause of his hyperuricemia?

Correct AnswerverifiedShow Answer

A nucleoside analogue that is being screened as a potential anticancer agent causes gout in clinical trials. Which of the following actions of this drug may cause gout?

Correct AnswerverifiedShow Answer

An enzyme system, isolated from the liver, converts deoxyuridine-5′-phosphate (dUMP) to thymidine-5′-phosphate (dTMP) . Which of the following participates in this reaction?

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

Methotrexate is an inhibitor of which of the following enzymes?

Correct AnswerverifiedShow Answer

The initial reaction of the de novo synthesis pathway for pyrimidine nucleotides begins with glutamine and CO2 and is complete with the formation of uridine monophosphate. Which of the following represents the rate-limiting enzyme in this pathway?

Correct AnswerverifiedShow Answer

Severe combined immunodeficiency disease (SCID) is characterized by a complete lack of cellmediated and humoral immunity. This disorder results from a deficiency in which of the following enzymes?

Correct AnswerverifiedAEXPLANATION: Severe combined immunodeficiency disease (SCID) is a disorder related to defects in the activity of the purine nucleotide catabolism enzyme, adenosine deaminase (ADA)

Allopurinol is an inhibitor of xanthine oxidase. Administration of allopurinol to a patient with gout and normal HGPRT levels would be expected to lead to which of the following?

Correct AnswerverifiedShow Answer

Which of the following groups of amino acids are nitrogen donors in purine ring biosynthesis?

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

A 37-year-old man presents with tophaceous deposits within the articular cartilage, synovium, tendons, tendon sheaths, pinnae, and the soft tissue on the extensor surface of the forearms. These clinical observations suggest the patient is suffering from which of the following disorders?

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

The gouty arthritis in patients with Lesch-Nyhan syndrome results from a genetic defect in which of the following enzymes?

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

In the synthesis of pyrimidines, which of the following molecules is a direct precursor of the pyrimidine ring?

Correct AnswerverifiedAEXPLANATION: Synthesis of the pyrimidines requires 1 mole of glutamine, 1 mole of ATP, and 1 mole of CO2 (which form carbamoyl phosphate) and 1 mole of aspartate. An additional mole of glutamine and ATP are required in the conversion of UTP to CTP

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

The initial reaction of the de novo synthesis pathway for pyrimidine nucleotides begins with glutamine and CO₂ and is complete with the formation of uridine monophosphate. Which of the following represents the rate-limiting enzyme in this pathway?

Correct Answer
verified

Correct Answer
verified
A
EXPLANATION: Severe combined immunodeficiency disease (SCID) is a disorder related to defects in the activity of the purine nucleotide catabolism enzyme, adenosine deaminase (ADA)

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified
A
EXPLANATION: Synthesis of the pyrimidines requires 1 mole of glutamine, 1 mole of ATP, and 1 mole of CO₂ (which form carbamoyl phosphate) and 1 mole of aspartate. An additional mole of glutamine and ATP are required in the conversion of UTP to CTP