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Step 1 Biochemistry Review


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Title: Step 1 Biochemistry Review

Step 1 Biochemistry Review
  • John W. Pelley, PhD

  • 6-630pm Carbohydrate metabolism review
  • Break
  • 630-7 pmLipid metabolism review
  • Lunch
  • 7-730pm Amino Acids and Nitrogen metabolism
  • Break
  • 730-8pm Molecular biology Proteins, Enzymes, and
    Misc Topics review

Carbohydrate Metabolism
  • 1. A 3-year-old African-American male has been
    diagnosed with malaria. He has become anemic
    after starting therapy with primaquine.
    Laboratory analysis reveals an increase in
    circulating reticulocytes and urine analysis
    reveals hemoglobinuria. Which of the following is
    the most likely cause of the hemoglobinuria?
  • A. Defect in the ß-globin chain
  • B. Defect in ß-globin chain synthesis
  • xC. Deficiency of glucose-6-phosphate
    dehydrogenase (G6PD)
  • D. Inhibition of pyruvate kinase
  • E. Reduced dietary iron absorption

  • 2. A 20-year-old male reports painful cramps
    during exercise. The cramps are usually followed
    by a red tint in his urine. Consumption of
    glucose containing electrolyte replacement drinks
    before exercising does not alleviate the
    symptoms. Additional tests indicate that he has a
    mild case of hemolytic anemia. The patient most
    likely has a deficiency of which of the following
  • A. Branching enzyme
  • B. Glucose-6-phosphatase
  • C. a-Glucosidase
  • D. Liver phosphorylase
  • xE. Phosphofructokinase (PFK)

  • 3. A 1-year-old boy has liver cirrhosis and
    hypotonia. His urine is negative for reducing
    substances. What enzyme associated with
    carbohydrate metabolism is most likely causing
    this childs condition?
  • A. Aldolase B
  • B. Galactose-1-phosphate uridyltransferase
  • C. Glucose-6-phosphatase
  • xD. Glucosyl (46) transferase
  • E. Liver phosphorylase

  • 4. A 3-month-old boy has progressive hepatomegaly
    and mild fasting hypoglycemia. Laboratory studies
    show that when the boy is fasting lactic acidosis
    is absent. A biopsy of liver tissue shows that
    the glycogen granules have an abnormal structure.
    The patient most likely has a deficiency of what
  • A. Branching enzyme
  • xB. Debranching enzyme
  • C. Glucose-6-phosphatase
  • D. a-Glucosidase
  • E. Liver phosphorylase

  • 5. A 2-month-old female infant has coarse facial
    features, mental retardation, corneal clouding,
    and hepatomegaly. Analysis of fibroblasts
    cultured from the patient most likely shows a
    deficiency in what enzyme?
  • A. Glucosidase
  • B. Hexosaminidase
  • xC. a-l-Iduronidase
  • D. Phosphotransferase
  • E. Sphingomyelinase

  • 6. A 25-year-old male medical student who has had
    diabetes mellitus since the age of 11 is
    unconscious when admitted to the emergency
    department. His wife suspects that he has not
    been injecting his insulin on a regular basis.
    His breath has a fruity odor and his blood
    glucose is 600 mg/dL. Glucose and ketone bodies
    are present in the urine. What substance is most
    responsible for the patients hyperglycemia?
  • A. Cortisol
  • B. Epinephrine
  • xC. Glucagon
  • D. Growth hormone
  • E. Thyroxine

  • 7. A 5-year-old male has had psychomotor
    retardation and a chronic lactic acidosis since
    birth. His fasting blood glucose is 100 mg/dL and
    he is not anemic. Which of the following is most
    likely deficient in this patient?
  • A Phosphoenolpyruvate carboxykinase
  • B. Pyruvate carboxylase
  • xC. Pyruvate dehydrogenase
  • D. Pyruvate kinase

  • 8. A 3-year-old male is brought to the
    pediatrician with failure-to-thrive. Physical
    examination of the patient reveals hepatomegaly.
    The fasting blood glucose is 30 mg/dL and no
    increase in the fasting blood glucose is seen
    with a glucagon challenge test is performed. The
    patient most likely has a deficiency of which of
    the following enzymes?
  • A Aldolase B
  • B. Fructokinase
  • C. Galactokinase
  • D. Galactose-1-phosphate uridyltransferase
  • xE. Glucose-6-phosphatase

  • 9. An 18-year-old male has a history of episodes
    of jaundice since birth. Physical examination
    shows conjunctival pallor and splenomegaly. Blood
    analysis reveals slightly increased indirect
    bilirubin, no elevation of homocysteine, and
    normocytic anemia with increased peripheral blood
    reticulocytes. Numerous spiculated red blood
    cells (RBCs) are apparent in the peripheral
    smear. The patient most likely has impaired
    activity for which of the following enzymes?
  • A Homocysteine methyltransferase
  • B. Glucose-6-phosphate dehydrogenase (G6PD)
  • C. Pyruvate dehydrogenase
  • xD. Pyruvate kinase

  • 10. A 25-year-old male of Greek descent complains
    of prolonged fatigue after a recent illness.
    Blood analysis shows normocytic anemia and urine
    analysis shows hemoglobinuria. Which of the
    following is the most likely cause of this
    patients anemia?
  • xA decreased glutathione peroxidase activity
  • B. iron deficiency
  • C. folate deficiency
  • D. reduced concentrations of ATP
  • E. reduced concentrations of NADH

  • 11. A 33-year-old female alcoholic complains of
    tiredness and disorientation approximately 6
    hours after a cocktail party. Her blood glucose
    is at 25 mg/dL. Which of the following would you
    expect to find elevated in her bloodstream?
  • A Ethanol
  • xB. Lactic acid
  • C. Chylomicrons
  • D. Acetate

  • 12. A 7 year old male was brought to the clinic
    by his mother with the complaint that he was
    having episodes of acting and talking as if he
    were drunk. These episodes occurred after
    stressful periods such as a febrile illness or
    fatigue. On examination the boy showed rapid
    breathing and rapid heart rate. Laboratory
    analysis showed elevated blood lactate and blood
    pyruvate, although the lactate to pyruvate ratio
    was normal. Blood pH was slightly acid at 7.30
    (normal 7.35-7.45). Blood glucose and ketones
    were normal. No ragged red fibers were observed
    in a skeletal muscle biopsy. What is the most
    likely diagnosis?
  • A hypoxia
  • B. pyruvate carboxylase deficiency
  • C. mitochondrial disease
  • xD. pyruvate dehydrogenase deficiency

  • 13. A 6 day-old female full term infant was
    brought to the emergency room with an enlarged
    liver, jaundice, failure-to-thrive, and urinary
    excretion of reducing sugars and albumin. Blood
    analysis showed a normal hemoglobin level and an
    elevated serum AST and ALT. Urinalysis with
    glucose oxidase was negative. She tolerated
    feeding with sucrose, maltose, glucose, and
    fructose at doses of 2 g/kg, but she vomited
    after lactose feeding. What other tissues will be
    affected by this disease?
  • A Red blood cells
  • B. spleen
  • C. Heart muscle
  • xD. Lens of the eye
  • E. CNS

  • 14. A 56-year-old male complains of chest pain
    associated with shortness of breath and fatigue.
    A coronary angiogram indicates 85 blockage of
    the left anterior descending coronary artery.
    Which of the following pumps is most directly
    affected by this myocardial ischemia?
  • A Calcium
  • B. bicarbonate
  • C. Potassium
  • xD. Proton
  • E. Sodium 

  • 15. A 25-year-old male is brought to the
    emergency room after falling from a ladder. He
    has sustained a ruptured spleen and is going into
    hypovolemic shock as a result of blood loss. He
    is conscious and his respiratory rate is
    elevated. Which of the following biochemical
    processes is most likely increased in this
  • xA anion gap
  • B. electron transport chain
  • C. Na/KATPase
  • D. citric acid cycle activity
  • E. oxidative phosphorylation

  • 16. A 5 year old male is examined by his
    pediatrician for fatigue, nausea, and
    lightheadedness brought on when meals are
    skipped. Physical examination reveals
    hepatomegaly. Laboratory results indicate lactic
    acidosis, hyperlipidemia, elevated serum uric
    acid, and marked hypoglycemia. Administration of
    fructose did not result in conversion to glucose.
    What other organs would be expected to be
  • xA kidney
  • B. spleen
  • C. heart
  • D. brain
  • E. skeletal muscle

Lipid Metabolism
  • 17. A 59 year old male complained during an
    annual physical exam of aching in his thighs
    during his 5 mile morning runs. No significant
    changes were made in the length or speed of the
    running schedule. He has a history of elevated
    blood lipids and has been taking a standard daily
    dose of a statin drug for the past two years. A
    routine laboratory profile was normal, but the
    creatine phosphokinase (CPK) value was elevated.
    What deficiency is created by the statin drug
    that is causing the symptoms?
  • xA isoprene
  • B. cholesterol
  • C. dehydroepiandrosterone
  • D. vitamin D

  • 18. A 52-year-old man with chronic alcoholism has
    a plasma lipid profile that contains an increase
    in very-low-density lipoprotein (VLDL). The
    mechanism that best explains the increase in VLDL
    in both the blood and liver in chronic alcoholics
  • A. impaired function of apolipoprotein B-100
  • B. inactivation of capillary lipoprotein lipase
  • C. increased ß-oxidation of fatty acids
  • xD. increased synthesis of glycerol 3-phosphate

  • 19. A 3-month-old boy has rapidly progressive
    central nervous system (CNS) deterioration,
    spasticity, and failure to thrive. Physical
    examination is significant for marked
    hepatosplenomegaly. Liver biopsy shows an
    increase of sphingomyelin in the lysosomes. What
    enzyme is most likely deficient in this infant?
  • A. Arylsulfatase A
  • B. Hexosaminidase A
  • C. Liver phosphorylase
  • xD. Sphingomyelinase

  • 20. A 25-year-old woman sees her physician
    because of exhaustion and diarrhea. Physical
    examination shows that she has low blood
    pressure, and blood studies show that she is
    anemic. Other studies show that she has a tumor
    of the pituitary gland that could produce
    hypofunction. Which of the following metabolic
    conversions is most likely affected by this
    pituitary tumor?
  • A. cortisol from cholic acid
  • B. 7-dehydrocholesterol from cholesterol
  • C. mevalonate from HMG CoA
  • xD. pregnenolone from cholesterol
  • E. progesterone from pregnenolone 

  • 21. A 3-year-old girl who is listless about 4
    hours after eating is found to have a deficiency
    of carnitine. What substrate is most likely the
    childs primary energy source?
  • A. Branched-chain amino acids
  • B. Fatty acids
  • C. Fructose
  • xD. Glucose
  • E. Ketone bodies 

  • 22. A 22-year-old woman with poorly controlled
    gestational diabetes delivers a
    large-for-gestational age infant at 24 weeks.
    Within 6 hours after birth, the newborn has
    respiratory difficulties associated with
    tachypnea and cyanosis. What substance is most
    likely deficient in this newborn?
  • A. Cardiolipin
  • B. Ceramide
  • xC. Dipalmitoyl phosphatidylcholine
  • D. Ganglioside
  • E. Sphingomyelin

  • 23. A 3-year-old child has ambiguous genitalia,
    diffuse pigmentation, and hypertension.
    Laboratory studies show an increase in plasma
    adrenocorticotropic hormone, a decrease in serum
    cortisol, and an increase in urine
    17-ketosteroids. Chromosome analysis shows an XX
    genotype. What enzyme involved in adrenal steroid
    synthesis is most likely deficient in this
  • xA. 11ß-Hydroxylase
  • B. 17a-Hydroxylase
  • C. 18-Hydroxylase
  • D. 21-Hydroxylase

  • 24. A 1-year-old child has hypertension, diffuse
    pigmentation, and female external genitalia. A
    chromosome analysis shows an XY genotype. The
    plasma adrenocorticotropic hormone concentration
    is increased, serum cortisol is decreased, and a
    random urine potassium is increased. What enzyme
    involved in adrenal steroid synthesis is most
    likely deficient in this patient?
  • A. 11ß-Hydroxylase
  • xB. 17a-Hydroxylase
  • C. 18-Hydroxylase
  • D. 21-Hydroxylase

  • 25. A 23-year-old woman has just eaten a meal
    consisting mainly of carbohydrates. What best
    describes the activity of capillary lipoprotein
    lipase and hormone-sensitive lipase in the
    adipose tissue of this individual?
  • A. Decreased capillary lipoprotein
    lipaseDecreased hormone-sensitive lipase
  • B. Decreased capillary lipoprotein
    lipaseIncreased hormone-sensitive lipase
  • xC. Increased capillary lipoprotein
    lipaseDecreased hormone-sensitive lipase
  • D. Increased capillary lipoprotein
    lipaseIncreased hormone-sensitive lipase

  • 26. A 75-year-old man develops urinary retention.
    Findings on physical examination include an
    enlarged, soft prostate gland and a bladder that
    is distended to the height of the umbilicus. A
    renal ultrasound shows enlargement of the
    bladder, both ureters, and the calyceal system of
    both kidneys. The hormone responsible for the
    enlarged prostate is most likely produced by what
  • A. Aromatase
  • B. 17a-Hydroxylase
  • C. 21-Hydroxylase
  • D. Oxidoreductase
  • xE. 5a-Reductase 

  • 27. A 2-year-old child suffers from a rare
    genetic disease that is characterized by fat
    malabsorption, spinocerebellar degeneration,
    hemolytic anemia, and pigmented retinopathy.
    Total cholesterol and triacylglycerol levels are
    extremely low, and levels of chylomicrons, very
    low-density lipoprotein (VLDL), and low-density
    lipoprotein (LDL) are not detectable. The patient
    most likely has an abnormality associated with
    what apolipoprotein?
  • A. Apolipoprotein A (apoA)
  • xB. Apolipoprotein B (apoB)
  • C. Apolipoprotein C-II (apoC-II)
  • D. Apolipoprotein E (apoE) 

  • 28. A 16-year-old boy has bilateral Achilles
    tendon xanthomas. His father died of an acute
    myocardial infarction at 32 years of age. What
    biochemical defect is most likely responsible for
    the physical finding in this patient?
  • A. Decreased clearance of very-low-density
    lipoprotein (VLDL)
  • B. Deficient levels of apolipoprotein C-II
  • C. Deficient levels of apolipoprotein E
  • D. Deficient levels of capillary lipoprotein
  • xE. Deficient levels of low-density-lipoprotein
    (LDL) receptors

  • 29. A 48-year-old man is scheduled for a lipid
    profile. He is instructed to fast for 12 hours
    before the blood sample is drawn at 8 am the next
    day. Lipid analysis shows
  • Serum cholesterol 250 mg/dL
  • Serum high-density lipoprotein cholesterol 25
  • Serum triacylglycerol 300 mg/dL
  • A refrigerated plasma sample shows a creamy layer
    on the surface of the plasma, but the plasma
    itself is clear. What change best explains the
    appearance of the refrigerated sample?
  • xA. Increased level of chylomicrons
  • B. Increased level of chylomicrons and
    low-density lipoproteins (LDL)
  • C. Increased level of chylomicrons and
    very-low-density lipoproteins (VLDL)
  • D. Increased level of LDL
  • E. Increased level of VLDL 

  • 30. A 25-year-old female has just finished eating
    a lunch consisting of a ham sandwich, potato
    salad, orange juice, and vanilla ice cream. Which
    of the following is most likely to be increased?
  • A adenylate cyclase activity
  • B. protein kinase A activity
  • C. hormone-sensitive lipase activity
  • xD. lipoprotein lipase activity 

  • 31. A 43-year-old man with chronic renal failure,
    who requires hemodialysis, complains of
    generalized bone pain. Physical examination shows
    bowing of the legs and a sallow complexion. When
    the mans blood pressure is taken, his thumb
    flexes into his palm. A radiograph of the bones
    shows generalized osteopenia. The patient most
    likely has a deficiency of which of the following
  • A Niacin
  • B. Ascorbic acid
  • C. Vitamin A
  • xD. Vitamin D
  • E. Vitamin K 

Amino Acids and Nitrogen Metabolism
  • 32. A 2-month-old male is brought to the
    pediatrician to treat a worsening cough. Physical
    examination reveals a diaper rash and oral
    thrush. Radiography reveals a chest infiltrate
    consistent with Pneumocystis carinii pneumonia.
    Blood analysis shows a complete lack of
    lymphocytes. Which of the following enzymes is
    most likely deficient in this infant
  • xA Adenosine deaminase
  • B. Hypoxanthine-guanine phosphoribosyltransferase
  • C. Orotate phosphoribosyl transferase
  • D. Xanthine oxidase 

  • 33. A neonatal nurse notices that the urine
    produced by a newborn infant has the odor of
    maple syrup. What biochemical reaction is most
    likely defective?
  • A. Metabolism of aromatic amino acids
  • xB. Metabolism of branched-chain amino acids
  • C. Metabolism of sulfur-containing amino acids
  • D. One-carbon transfer reactions
  • E. Transformation of carbohydrates to amino acids 

  • 34. A healthy adult is placed on a diet that
    lacks tyrosine, but is otherwise balanced. As a
    result of this diet, nitrogen balance is most
    likely to
  • xA. be achieved
  • B. become negative
  • C. become positive
  • D. progress from a negative state to equilibrium
  • E. progress from a positive state to equilibrium

  • 35. A 42-year-old man is taking isoniazid to
    treat tuberculosis. He is most at risk of
    developing a deficiency of what amino acid?
  • A. Arginine
  • xB. Aspartate
  • C. Glutamate
  • D. Glutamine
  • E. Glycine 

  • 36. A 48-year-old man with cirrhosis of the liver
    is not oriented to time or place. After he is
    placed on a low-protein diet, he experiences some
    improvement in mental status. What enzyme is most
    likely responsible for these abnormalities in
    mental status?
  • A. Arginase
  • B. Argininosuccinate lyase
  • C. Argininosuccinate synthetase
  • xD. Carbamoyl phosphate synthetase I
  • E. Ornithine carbamoyltransferase 

  • 37. A 1-year-old child with mental retardation
    has a deficiency of dihydrobiopterin reductase.
    This enzyme deficiency is most closely related to
    what disorder?
  • A. Galactosemia
  • B. Maple syrup urine disease
  • C. Niemann-Pick disease
  • xD. Phenylketonuria (PKU)
  • E. Wilson disease 

  • 38. A 42-year-old man who works in a battery
    factory complains of fatigue, headaches,
    abdominal pain, and chronic diarrhea. Laboratory
    studies show a hemoglobin of 10 g/dL and a mean
    corpuscular volume (MCV) of 75 µm3. A peripheral
    blood smear shows hypochromic red blood cells
    (RBCs) with coarse basophilic stippling. What is
    an additional expected laboratory finding?
  • A. Decreased serum ferritin
  • B. Decreased zinc RBC protoporphyrin
  • C. Increased hemoglobin A2 (HbA2 ) and
    hemoglobin F (HbF)
  • xD. Increased urinary d-aminolevulinic acid (ALA) 

  • 39. A 1-year-old male child is brought to the
    pediatrician because his parents have noticed
    that the boy is mutilating himself by chewing on
    his lips. On examination, the child is found to
    be mentally retarded and manifesting signs of
    gouty arthritis. What enzyme involved in
    nucleoside metabolism is most likely deficient in
    this child?
  • A. Adenosine deaminase
  • xB. Hypoxanthine-guanine phosphoribosyltransferase
  • C. Phosphoribosylpyrophosphate synthase
  • D. Thymidine kinase
  • E. Xanthine oxidase 

  • 40. A 1-year-old boy has a history of recurrent
    bacterial and fungal infections. Serum protein
    electrophoresis shows a flat ?-globulin region.
    Further testing shows increased concentrations of
    dATP in white blood cells. What is the most
    likely diagnosis?
  • xA. Adenosine deaminase deficiency
  • B. Bruton agammaglobulinemia
  • C. Lesch-Nyhan syndrome
  • D. Oroticaciduria
  • E. Purine nucleoside phosphorylase deficiency 

  • 41. A full-term male infant begins to show
    irritability and lethargy 36 hours after birth.
    Laboratory studies show a plasma ammonia level
    that is 60 times normal and a urinary orotate
    level that is 100 times normal. What enzyme is
    most likely defective in this infant?
  • A. Arginase
  • B. Carbamoyl phosphate synthetase II
  • xC. Ornithine transcarbamoylase
  • D. Serine hydroxymethyltransferase 

  • 42. A 4-day-old infant has physiologic jaundice
    of the newborn. She receives phototherapy with
    blue light to reduce the level of bilirubin in
    her blood and eliminate jaundice in the skin.
    What mechanism best explains the manner in which
    phototherapy reduces jaundice?
  • A. Increases conjugating enzymes in the liver
  • B. Increases synthesis of vitamin D in the skin
  • C. Metabolizes bilirubin to biliverdin
  • xD. Oxidizes bilirubin to a water-soluble form

  • 43. A 28-year-old woman has an intermittent
    history of severe abdominal pain that typically
    occurs after she has consumed a few glasses of
    wine or after she has been on "crash diets." In
    visits to many different physicians over the past
    few years, she has undergone several laboratory
    tests (e.g., complete blood cell count,
    electrolytes), barium studies, and laparoscopic
    examinations, none of which has revealed the
    cause of her pain. Her physician now orders a
    urine specimen for culture. The woman collects
    the specimen and leaves it near a window for
    about 30 minutes, when she notices that the urine
    color has changed from pale yellow to wine-red.
    What compound is most likely responsible for the
    color change?
  • A. Hemoglobin
  • B. Myoglobin
  • xC. Porphobilin
  • D. Urobilin
  • E. Uroporphyrin I 

  • 44. A 5-year-old black child is brought to a
    medical missionary hospital in Africa. The child
    is apathetic, and physical examination shows
    reddish brown hair, a protuberant abdomen,
    hepatomegaly by percussion, ascites, and pitting
    edema of the lower extremities. What feature is
    most likely responsible for the hepatomegaly in
    this patient?
  • A. Decreased albumin content of the blood
  • B. Decreased ß-oxidation of fatty acids
  • xC. Decreased synthesis of apolipoproteins
  • D. Increased intake of fatty food
  • E. Increased synthesis of fatty acids 

  • 45. A 53-year-old male with chronic myelogenous
    leukemia has begun treatment with multiple
    antineoplastic agents. He soon develops renal
    failure. Urinalysis shows an acid pH and the
    presence of crystals that have become deposited
    in the renal tubules. What treatment will most
    likely help reduce the deposition of the crystals
    in the renal tubules?
  • A. increased fluids
  • xB. allopurinol
  • C. ciprofloxacin
  • D. lithotripsy
  • E. hydrochlorothiazides  

  • 46. A 38-year-old male has been diagnosed with
    tuberculosis. He is treated with isoniazid and
    rifampin. He develops a microcytic anemia
    associated with a high serum ferritin
    concentration. A bone marrow examination shows
    increased iron stores and numerous ringed
    sideroblasts. What enzyme is most likely affected
    by the chemotherapy?
  • A. Glucose-6-phosphate dehydrogenase
  • B. Methylmalonyl CoA mutase
  • C. Glutathione reductase
  • xD. d-aminolevulinic acid synthase
  • E. Methemoglobin reductase  

  • 47. A 32-year-old male complains of skin lesions
    that develop whenever his skin is exposed to
    sunlight. The problem is so severe that he always
    avoids sunlight. He also notes that his urine has
    become a wine-red color. Physical examination
    shows numerous fluid-filled vesicles on areas of
    skin most exposed to sunlight. Laboratory
    studies, including a complete blood cell count
    and electrolytes, are normal. He has a history of
    chronic hepatitis C. Which of the following is
    most likely responsible for the color change in
    the urine?
  • A Heme
  • B. Urobilin
  • C. Porphobilin
  • xD. Uroporphyrin I 

Molecular biology Proteins, Enzymes, and Misc
  • 48. A 4-year-old male has been deaf since birth
    and has a history of multiple fractures. Physical
    examination reveals a bluish discoloration of the
    sclera. Which of the following proteins is most
    likely defective?
  • A fibrillin
  • B. a-l-iduronidase
  • xC. type I collagen
  • D. type III collagen
  • E. Elastin 

  • 49. A 58-year-old female complains that her heart
    does flip-flops that keep her awake at night.
    Physical examination reveals bilateral
    exophthalmos, enlarged thyroid, and pretibial
    myxedema. Which of the following
    glycosaminoglycans is producing the pretibial
  • A Chondroitin sulfate
  • xB. Dermatan sulfate
  • C. Heparin
  • D. Hyaluronic acid
  • E. Keratan sulfate I 

  • 50. A 28-year-old man has a family history of a
    disabling disorder that has caused the deaths of
    his father, grandfather, and two paternal aunts.
    The father and aunts died at a younger age than
    did his grandfather, and it appears that the
    condition progressively worsens with each
    generation. What disorder is most likely?
  • A. Cystic fibrosis
  • B. Duchenne muscular dystrophy
  • xC. Huntington disease
  • D. Metachromatic leukodystrophy
  • E. Parkinson disease 

  • 51. A cell culture of a tumor biopsy is suspected
    of containing a ras oncogene. Which protein is
    most likely to confirm this diagnosis?
  • xA. G protein
  • B. Growth factor
  • C. Growth factor receptor
  • D. Nuclear transcription factor 

  • 52. A 48-year-old woman with type 2 diabetes
    mellitus complains of intermittent problems with
    blurry vision. Physical examination shows a
    normal lens and mild diabetic retinopathy. What
    would best evaluate the possibility that
    chronically elevated glucose levels contribute to
    this patients condition?
  • A. Blood glucose (fasting)
  • B. Blood ketones
  • xC. Hemoglobin A1c concentration
  • D. Serum C-peptide 

  • 53. A 53-year-old farmer has a raised crateriform
    lesion on the inner aspect of the bridge of his
    nose and numerous gray-white hyperkeratotic
    lesions on the face, hands, back of the neck, and
    forearms. What is most likely responsible for the
    pathogenesis of these lesions?
  • A. Cleavage of DNA strands
  • B. Defects in DNA repair enzymes
  • C. Point mutations resulting in stop codons
  • xD. Pyrimidine dimers resulting in distortion of
    the DNA helix 

  • 54. A 3-year-old black girl is brought to a
    physicians office for a routine physical
    examination. During the examination, pallor of
    the conjunctiva and mucous membranes is observed.
    The patient is of normal height for her age, but
    her weight is below normal. The girls cousin has
    sickle cell disease. A PCR-based restriction
    (polymerase chain reaction-based) analysis
    produces three bands of 103 bp, 191bp, and 234
    bp. Knowing that bands at 103 bp and 191 bp
    correspond to normal ß-globin DNA, and a single
    234-bp band is diagnostic for sickle cell anemia,
    what is the most likely diagnosis?
  • A. Further studies are necessary
  • B. Results of blood studies are normal
  • C. Sickle cell disease
  • xD. Sickle cell trait
  • E. ß-Thalassemia minor

  • 55. A 50-year-old man complains of weight loss,
    fatigue, weakness, and a sense of fullness in the
    left upper abdominal quadrant. Physical
    examination shows pallor, splenomegaly, and
    hepatomegaly there is no lymphadenopathy. Bone
    marrow aspirate shows 30 blasts. Laboratory
    studies show a leukocyte count of 300,000/mm3 and
    the Philadelphia chromosome. What gene is most
    likely associated with these findings?
  • xA. abl
  • B. brcal
  • C. c-myc
  • D. p53
  • E. Rb 

  • 56. A 48-year-old African-American woman who has
    widespread thickening of the skin is diagnosed
    with diffuse cutaneous scleroderma. Laboratory
    studies show the presence of autoantibodies to a
    nuclear enzyme that relieves torsional stress in
    DNA. This patient most likely produces
    autoantibodies to what enzyme?
  • A. Endonuclease
  • B. Exonuclease
  • C. Helicase
  • D. Ligase
  • xE. Topoisomerase I 

  • 57. The parents of a 2-year-old child bring their
    son to the pediatricians office during a family
    vacation in Florida. They have noticed that after
    playing on the beach for several days, the boy
    has developed blisters and redness on his face,
    extremities, and trunk. He also has multiple
    freckles over the face, lips, and extremities, as
    well as pigmented patches interspersed with
    hypopigmented areas. What process is most likely
    to be defective in this child?
  • xA. DNA repair
  • B. DNA replication
  • C. mRNA splicing
  • D. Protein translation
  • E. RNA transcription 

  • 58. A 20-year-old healthy woman with a family
    history of hereditary nonpolyposis colorectal
    cancer (HNPCC) has genetic testing and is found
    to be a carrier of the HNPCC gene. Genetic
    testing shows a mutation in a gene encoding a DNA
    repair protein. This protein most likely
    participates in which type of DNA repair?
  • A. Base excision
  • B. Depurination
  • C. Nucleotide excision
  • xD. Postreplication mismatch
  • E. Recombinational 

  • 59. A child of healthy parents has an autosomal
    recessive disorder. The 0.5 kb DNA fragment of
    the normal gene amplified by polymerase chain
    reaction (PCR) contains a BamHI restriction site.
    On digestion with BamHI, this fragment yields two
    fragments, which are 0.2 kb and 0.3 kb long. This
    restriction site is lost in the mutated gene
    thus PCR amplification yields a 0.5 kb DNA
    fragment that is not sensitive to digestion with
    BamHI. The PCR-amplified 0.5 kb DNA fragments
    from both parents are subjected to BamHI
    treatment and electrophoresis. Which of the
    following DNA patterns is most likely seen on the
  • A. DNA of at least one parent has no 0.5 fragment
  • B. DNA of at least one parent has neither 0.2 nor
    0.3 kb fragments
  • xC. DNA of each parent separates into 0.2, 0.3,
    and 0.5 kb fragments
  • D. Maternal DNA migrates as a single 0.5 kb
  • E. Paternal DNA migrates as a single 0.5 kb

  • 60. A 27-year-old man complains of genital sores.
    The patient reports recent unsafe sexual contact.
    Examination of fluid from a bulla reveals
    multinucleated giant cells with intranuclear
    inclusions (Tzank cells). Which of the following
    enzymes is the best target for therapy?
  • A Adenosine deaminase
  • B. Hypoxanthine-guanine phosphoribosyltransferase
  • C. Phosphoribosylpyrophosphate (PRPP) synthase
  • xD. Thymidine kinase
  • E. Xanthine oxidase 

  • 61. A 59-year-old male complains of a
    progressively worsening cough, drenching night
    sweats, and increasing fatigue. He is diagnosed
    with Mycobacterium tuberculosis infection. The
    patient is prescribed a four-drug regimen,
    including rifampin. Which of the following
    bacterial sites is inhibited by the rifampin?
  • A acyl carrier protein
  • xB. RNA polymerase
  • C. arabinosyl transferase
  • D. ribosomal protein

  • 62. A three year old male is brought to the
    pediatrician because he has begun to stumble and
    has obvious difficulty running, jumping, and
    climbing stairs. His calf muscles have also
    become noticeably enlarged. Deletion scanning PCR
    revealed an absent band from the dystrophin gene
    after electrophoresis and blotting. What does the
    missing band represent?
  • A promoter
  • xB. exon
  • C. enhancer
  • D. splice site 

  • 63. A 24-year-old man returns from a trip to
    India and has profuse, watery diarrhea and a
    feeling of lightheadedness when he stands. A Gram
    stain of stool shows comma-shaped gram-negative
    organisms and an absence of an inflammatory
    reaction. What most accurately describes the
    biochemical alterations underlying this patients
  • A. Activation of a Gq protein
  • xB. Activation of a Gs protein
  • C. Inactivation of a Gi protein
  • D. Inhibition of a Cl channel
  • E. Stimulation of guanylyl cyclase activity

  • 64. After exercising strenuously for 1 hour, a
    23-year-old healthy man drinks two glasses of
    wine. He suddenly feels dizzy and has a rapid
    heartbeat and clammy skin. Which mechanism is
    most likely responsible for this mans reaction
    to alcohol?
  • A. Gluconeogenesis is inhibited by the abundance
    of oxaloacetate
  • B. Gluconeogenesis is inhibited by the abundance
    of pyruvate
  • C. Glycogenolysis is inhibited by ethanol
  • D. NADH is used in ethanol metabolism
  • xE. Oxaloacetate and pyruvate are diverted from
    the gluconeogenetic pathway

  • 65. An 18-year-old male complains of a rash and
    hair loss to his physician. He reports that in
    addition to a balanced diet he eats about 20 raw
    eggs per day to enhance his body-building
    exercises. What additional symptom is most likely
    in this patient?
  • A. bleeding gums
  • B. dementia
  • C. glossitis
  • xD. lactic acidosis
  • E. nystagmus 

  • 66. A 62-year-old woman whose husband died
    recently has developed a vitamin deficiency due
    to adopting a diet consisting of cereal and diet
    cola. She complains of bleeding gums after
    brushing her teeth and pain in her legs when she
    walks. Physical examination shows a smooth red
    tongue, gingivitis, carious teeth, scattered
    ecchymoses over the trunk, and pinpoint areas of
    hemorrhage around the hair follicles. Which one
    of the following reactions most likely accounts
    for these physical findings?
  • A. Cleavage of N- and C-terminal propeptide
  • B. Formation of pro-a-chains
  • C. Glycosylation of side-chain residues
  • xD. Hydroxylation of proline and lysine
  • E. Triple helix assembly of procollagen 

  • 67. A 42-year-old woman with severe rheumatoid
    arthritis begins taking an immunosuppressive
    drug. A few weeks later, she develops moderately
    severe macrocytic anemia, with pancytopenia and
    hypersegmented neutrophils. The most likely
    mechanism underlying this drug-induced anemia
    involves inhibition of
  • xA. Dihydrofolate reductase
  • B. Intestinal conjugase
  • C. Production of intrinsic factor
  • D. Reabsorption of folate 

  • 68. A 38-year-old woman with chronic alcoholism
    has been homeless for the past year. Her diet
    consists primarily of starchy processed "junk"
    foods, in addition to alcoholic beverages.
    Physical examination shows noticeably thickened
    skin and the presence of hyperkeratotic hair
    follicles. The conjunctivae are dry, and tear
    production is reduced. What other finding is most
    likely to be expected?
  • A. Bleeding gums
  • B. Hemolytic anemia
  • xC. Impaired night vision
  • D. Osteomalacia
  • E. Pain in the long bones 

  • 69. A 25-year-old medical student who has had
    diabetes mellitus since childhood is unconscious
    when admitted to the emergency room. His wife
    states that he has been studying for an
    examination for the past 2 days and has not been
    injecting his insulin on a regular basis.
    Physical examination shows a blood pressure of
    80/40 mm Hg, heart rate of 124 beats/min, and
    respiratory rate of 35 breaths/min. His breath
    has a fruity odor, and his skin turgor is poor.
    What additional finding is most likely to be
  • A. blood sodium
  • B. blood lactate
  • C. blood pH
  • D. serum bicarbonate
  • xE. anion gap 

  • 70. A 25-year-old man who has been homeless for
    several months is admitted to the hospital in a
    state of starvation. He has not eaten anything in
    the past week. He is started on a diet in which
    60 of the calories come from carbohydrates. This
    diet would most likely increase the activity of
    what enzyme?
  • A. Carnitine acyltransferase
  • B. Citrate synthase
  • xC. Glucokinase
  • D. Glucose-6-phosphatase
  • E. HMG-CoA synthase

  • 71. A 23-year-old woman, who has had diabetes
    mellitus since the age of 10, is unconscious when
    admitted to the emergency room. Physical
    examination shows a blood pressure of 80/40 mm
    Hg, heart rate of 124 beats/min, and respiratory
    rate of 35 breaths/min. She has poor skin turgor
    and a fruity odor to her breath. Her blood
    glucose level is 750 mg/dL. What enzyme is most
    likely responsible for the presence of a fruity
    odor on this patients breath?
  • A. Acetyl-CoA carboxylase
  • B. Citrate lyase
  • C. HMG-CoA reductase
  • xD. HMG-CoA synthase
  • E. Pyruvate dehydrogenase 

  • 72. During a physical examination of a
    24-year-old man who is mentally retarded, the
    physician notices clumsiness and spasticity of
    the patient's limbs, emotional lability, and
    decreased visual-spatial discrimination.
    Laboratory studies show spherical granular masses
    in urinary sediment that stain positive with PAS
    and Alcian blue. The patient most likely has a
    deficiency of what enzyme?
  • xA. Arylsulfatase A
  • B. a-Glucosidase
  • C. Hexosaminidase A
  • D. Muscle phosphorylase
  • E. Sphingomyelinase 

  • 73. An otherwise healthy 1-year-old girl has
    fasting hypoglycemia after eating a meal
    containing carbohydrates. Extended fasting does
    not result in ketosis or lactic acidosis. The
    patient most likely has what disorder?
  • A. Glycogen storage disease type VI
  • xB. Medium-chain acyl CoA dehydrogenase
  • C. Pyruvate carboxylase deficiency
  • D. Thiamine deficiency 

  • 74. A 65-year-old man with a known history of
    chronic alcoholism complains of severe chest pain
    that radiates down the inside of his left arm. An
    ECG shows a prior acute anterior myocardial
    infarction (MI). A complete blood cell count
    shows a macrocytic anemia with hypersegmented
    neutrophils and mild pancytopenia. No neurologic
    abnormalities are evident. The plasma
    homocysteine level is increased. What best
    explains the increase in plasma homocysteine in
    this patient?
  • A. Decreased level of cystathionine synthase
  • B. Decreased level of dihydrofolate reductase
  • C. Decreased level of thymidylate synthetase
  • xD. Decreased serum folate
  • E. Decreased serum vitamin B12 

  • 75. A 52-year-old man with chronic bronchitis
    requires continuous supplementary O2 to maintain
    an adequate arterial PO2. What would most likely
    improve O2 delivery to this patients tissues?
  • xA. Decreased arterial pH
  • B. Decreased red blood cell 2,3-bisphosphoglycerat
    e (2,3-BPG)
  • C. Decreased temperature
  • D. Hyperventilation 

  • 76. A 3-year-old child shows signs of mental
    deterioration and skeletal deformities.
    Microscopic and laboratory analyses show enlarged
    lysosomes and increased levels of lysosomal
    enzymes in the serum. These findings are most
    likely caused by a defect in what process?
  • A. Gene amplification
  • xB. Mannose 6-phosphate attachment
  • C. Nuclear localization signal
  • D. Transferrin receptor mRNA 

  • 77. A 25-year-old woman complains of chest pain.
    On physical examination, a midsystolic click is
    audible, followed by a late systolic murmur,
    indicating a valvular disease. What
    glycosaminoglycan is associated with the valvular
  • A. Chondroitin sulfate
  • xB. Dermatan sulfate
  • C. Heparan sulfate
  • D. Hyaluronic acid
  • E. Keratan sulfate 

  • 78. A 40-year-old man of Scandinavian descent
    sees his physician with complaints of shortness
    of breath and a nonproductive cough. He has
    smoked one pack of cigarettes daily for 30 years.
    A chest radiograph shows increased lung volume,
    and the diaphragm appears flatter than normal.
    The suspected diagnosis is emphysema because of
    an enzyme deficiency. This deficiency most likely
    results in
  • A. decreased collagen cross-linking
  • B. defective collagen fiber synthesis
  • C. defective a-keratin synthesis
  • xD. increased neutrophil elastase
  • E. mutated elastin protein 

  • 79. A 3-year-old male with nephrotic syndrome has
    a urine protein level gt4 g/day. Physical
    examination reveals generalized edema and
    ascites. What best describes the effect on
    calcium in his serum?
  • A. Decreased ionized calcium
  • xB. Decreased total calcium
  • C. Normal total calcium
  • D. Increased ionized calcium

  • 80. A 23-year-old male is admitted to the
    emergency room after an evening of dancing at a
    rock concert. He reports that he took a large
    number of poppers to increase his enjoyment at
    the concert. He has a bluish discoloration to his
    lips, palms of his hands, and his fingernails.
    Arterial blood gas analysis shows a normal p02
    but the blood is a chocolate-brown color.
    Administration of pure O2 does not improve the
    bluish discoloration. Which of the following is
    the most likely diagnosis?
  • A glucose 6-phosphate deficiency
  • B. carbon monoxide poisoning
  • xC. methemoglobinemia
  • D. iron deficiency anemia 

  • 81. A 15 year old female complains of fatigue.
    Her laboratory results indicate her serum iron is
    7.5 mmole/liter. Which of the following will most
    likely be elevated by the indicated therapy?
  • xA transferrin
  • B. ceruloplasmin
  • C. ferritin
  • D. haptoglobin
  • E. albumin 

  • 82. A 45 year old woman developed dementia,
    myoclonus, weakness and spasticity. She became
    comatose within months after onset of
    neurological signs. Postmortem brain biopsy
    showed spongiform encephalopathy consistent with
    Creutzfeldt-Jakob disease. Several
    encephalopathies including Creutzfeldt-Jakob are
    thought to be caused by prions. What level of
    protein structure is altered by prions?
  • A primary structure
  • xB. secondary structure
  • C. tertiary structure
  • D. quaternary structure

  • 83. A 42-year-old male who works at a firing
    range complains of headaches, loss of sensation,
    weakness, a metallic taste in the mouth, and
    uncoordinated walking. Laboratory studies show a
    hemoglobin of 9 g/dL and a mean corpuscular
    volume (MCV) of 70 µm3. His red blood cells
    (RBCs) are hypochromic with coarse basophilic
    stippling. What is an additional expected
    laboratory finding?
  • A. Decreased serum ferritin
  • B. Decreased zinc RBC protoporphyrin
  • C. Increased hemoglobin A2 (HbA2) and hemoglobin
    F (HbF)
  • xD. Increased urinary d-aminolevulinic acid