Block 10 Heme Purine Pyrimidine MCQ's

13 Questions | Total Attempts: 630

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Block 10 Heme Purine Pyrimidine MCQ

Questions and Answers
  • 1. 
    A 44-year old woman presents to her physician with loss of appetite, fatigue, muscle weakness and depression. Initial blood analysis shows she has anemia. A bone marrow aspirate confirmed the suspicion that she has a megaloblastic anemia. Serum folic acid level was 2.9 ng/m1 (normal= 6-15), Her serum B12 level was 153 pg/ml (normal=150-75C). The patient's      megaloblastic anemia is most likely caused by
    • A. 

      A decreased synthesis of rnethionine

    • B. 

      A decreased conversion of dUMP to dTMP

    • C. 

      A decrease in the synthesis of oxaloacetate

    • D. 

      A decrease in the leves of succinyl CoA.

    • E. 

      A decreased synthesis of dUMP.

  • 2. 
    A deficiency in thiamine would most likely lead to which of the following clinical manifestations?
    • A. 

      A decrease in carboxylase activity

    • B. 

      A decrease in serum lactate concentrations

    • C. 

      A decrease in red blood cell tranketolase activity

    • D. 

      An increase in urinary methylmalonic acid

    • E. 

      An increase in prothrornbin time

  • 3. 
    An apparently healthy 5-month-old female infant was brought to the pediatrician's office by her mother with the complaints of periodic bouts of vomiting and failure to gain weight. The mother reported that the child would also have periods of irritability and lethargy. Blood analysis revealed increased levels of plasma ammonia and glutamine coupled with decreased plasma citrulline. Orotic acid was found in her urine. This child is most likely to have a deficiency of:
    • A. 

      N-acetyl glutamate synthetase

    • B. 

      Carbamoyl phosphate synthetase I

    • C. 

      Ornithine transcarbamoylase

    • D. 

      Carbamoyl phosphate synthetase II

    • E. 

      Arginosuccinate lyase

  • 4. 
    A deficiency of which of the labeled substances is responsible for the symptoms that are associated with severe combined immunodeficiency syndrome?
    • A. 

      A

    • B. 

      B

    • C. 

      C

    • D. 

      D

    • E. 

      E

  • 5. 
    A 52-year-old woman presented to the emergency room with severe generalized abdominal pains. She had been vomiting, was constipated and had a distended abdomen. Her history showed that she had recently been prescribed gresiofulvin and sulfonamide for a persistent infection. Urine analysis revealed a remarkably elevated level of porphobilinogen. The drugs were discontinued arid the patient's condition improved. The most likely cause of the patient's difficulty was:
    • A. 

      A deficiency in one of the heme biosynthesis enzymes located late in the pathway after synthesis of porphyrin

    • B. 

      A deficiency in uroporphyrinogen III cosynthase, leading to the appearance of hydroxyrnethylbilane in the urine

    • C. 

      Abnormally low activity of delta-aminolevulinate (6-ALA) dehyciratase, leading to accumulation of 6-ALA in the urine

    • D. 

      Abnormally high 6-ALA synthase activity, leading to elevated steady state production of porphobilinogen which was excreted in the urine

  • 6. 
    A 21-year-old healthy male celebrates his 21st birthday with friends and because of the occasion they persuade him to have a beer. After consuming the beer he begins to get intense abdominal pain which worsens with time. His friends take him to the emergency because he begins to suffer nausea and vomiting. Upon arrival he is noted to be anxious, has tachycardia and hypertension. Laboratory analysis reveals elevated serum and urine aminolevulinic (ALA) and porphobilinogen (PBG). He most likely has which of the following enzyme deficiency?
    • A. 

      Uroporphyrinogen decarboxylase

    • B. 

      Delta-ALA dehydratase

    • C. 

      Delta-ALA synthase

    • D. 

      PBG-Deaminase

    • E. 

      Ferrochelatase

  • 7. 
    A chemotherapeutic agent that affects both pyrimidine metabolism and RNA is?
    • A. 

      Methotrexate

    • B. 

      Leflunomide

    • C. 

      Azaserine

    • D. 

      Hydroxyurea

    • E. 

      5-Fluorouracil

  • 8. 
    A 48-year-old man who has been a heavy drinker of alcohol for the past three years presents to the physician with what looks like a red rash all over the exposed parts of his skin. The physician orders a urine sample for analysis. He collects the specimen and in the laboratory the technician notices that it has turned color from yellow to pink under fluorescent light. Which of the following enzymes is most likely deficient in this patient?
    • A. 

      Uroporphyrinogen decarboxylase

    • B. 

      Porphobilinogen deaminase

    • C. 

      Mitochondrial ferrochelatase

    • D. 

      ALA synthase

    • E. 

      UDP glucoronyl transferase

  • 9. 
    A-2-month-old infant is brought to the pediatrician because his mother notices that he has a cough which is not getting better even on over the counter (OTC) medication. On physical examination the doctor sees that the child also has a diaper rash which she considers to be very bad and notes that he is below the 5'h percentile for all growth curves, A chest radiograph reveals that the child has pneumonia and a complete blood cell count shows that lymphocytes are absent. Which of the following enzymes would most likely be deficient in this infant?
    • A. 

      Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)

    • B. 

      Dihydroorotate dehyclrogenase

    • C. 

      Xanthine oxidase

    • D. 

      Purine nucleoside phosphorylase

    • E. 

      Adenosine deaminase

  • 10. 
    A 53-year-old man presents to the emergency room. He tells the physician that he has had a 10-day history of anorexia, nausea and flu-type symptoms. He commented that his urine was dark in color for the past three days. A physical examination revealed tenderness in the right upper quadrant of the abdomen. A urine dipstick test was positive for bilirubin and urobilinogen. Liver function test were as follows: This patient most likely has:
    • A. 

      Liver cirrhosis

    • B. 

      Obstructive jaundice

    • C. 

      Hemolytic anemia

    • D. 

      Dubin-Johnson syndrome

    • E. 

      Viral hepatitis

  • 11. 
    A medical student recovering from an attack of influenza was noticed to be slightly jaundiced. Worried that he might have hepatitis the student has a blood sample taken for biochemical analysis. The results are shown below:
    • A. 

      Cholestasis

    • B. 

      Hemolytic jaundice

    • C. 

      Excess alcohol consumption

    • D. 

      Gilbert's syndrome

    • E. 

      Dubln-Johnson syndrome

  • 12. 
    A child with penicillin allergy is given a sulphonamide against otitis media. Human cells are not affected by sulphonamides because sulphonamides are specific for bacterial
    • A. 

      DNA polymerases

    • B. 

      RNA poymerases

    • C. 

      Ribonucleotide reductase

    • D. 

      Mismatch repair

    • E. 

      Folate synthesis

  • 13. 
    You are a neonatologist working in a tertiary care hospital in a state capital. A 4-week old male is transferred to you with severe jaundice that appeared at birth and has been worsening ever since. The boy is the first child of a healthy Jewish couple, pregnancy and vaginal delivery were unremarkable. The boy is of average height and weight for his age, in no acute distress, but shows marked jaundice and slight hepatomegaly. Lab: CBC normal, indirect bilirubin high, low fecal urobilinogen. What is the most likely diagnosis?
    • A. 

      Neonatal jaundice

    • B. 

      Dubin-Johnson syndrome

    • C. 

      Rotor (-Manahan-Florentin) syndrome

    • D. 

      Glucose-6-phosphate dehydrogenase deficiency

    • E. 

      Uridyl glucuronyl transferase deficiency