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Schedule
• 6-6:30pm Carbohydrate metabolism review– Break
• 6:30-7 pmLipid metabolism review– Lunch
• 7-7:30pm Amino Acids and Nitrogen metabolism review– Break
• 7:30-8pm Molecular biology Proteins, Enzymes, and Misc Topics review
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Carbohydrate Metabolism
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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 β-globin chainB.Defect in β-globin chain synthesisxC. Deficiency of glucose-6-phosphate
dehydrogenase (G6PD)D.Inhibition of pyruvate kinaseE. Reduced dietary iron absorption
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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 enzymes?
A.Branching enzyme B.Glucose-6-phosphataseC. α-GlucosidaseD.Liver phosphorylasexE. Phosphofructokinase (PFK)
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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 child’s condition?
A.Aldolase BB.Galactose-1-phosphate uridyltransferaseC.Glucose-6-phosphatasexD. Glucosyl (4:6) transferaseE.Liver phosphorylase
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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 enzyme?
A.Branching enzymexB. Debranching enzymeC. Glucose-6-phosphataseD.α-GlucosidaseE. Liver phosphorylase
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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.GlucosidaseB.HexosaminidasexC. α-l-IduronidaseD. PhosphotransferaseE.Sphingomyelinase
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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 patient’s hyperglycemia?
A. Cortisol B. EpinephrinexC. GlucagonD. Growth hormoneE. Thyroxine
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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 carboxykinaseB.Pyruvate carboxylasexC. Pyruvate dehydrogenaseD. Pyruvate kinase
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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 BB.FructokinaseC. GalactokinaseD.Galactose-1-phosphate uridyltransferasexE. Glucose-6-phosphatase
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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 methyltransferaseB.Glucose-6-phosphate dehydrogenase (G6PD)C. Pyruvate dehydrogenasexD. Pyruvate kinase
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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 patient’s anemia?
xA decreased glutathione peroxidase
activityB.iron deficiencyC.folate deficiencyD. reduced concentrations of ATPE.reduced concentrations of NADH 13
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 EthanolxB. Lactic acidC.ChylomicronsD. Acetate
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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 hypoxiaB. pyruvate carboxylase deficiencyC. mitochondrial diseasexD. pyruvate dehydrogenase deficiency
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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 cellsB. spleenC. Heart musclexD. Lens of the eyeE. CNS
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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 CalciumB.bicarbonateC. PotassiumxD. ProtonE. Sodium
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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 patient?
xA anion gapB.electron transport chainC. Na+/K+ATPaseD.citric acid cycle activityE. oxidative phosphorylation
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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 enlarged?
xA kidneyB. spleenC. heartD. brainE. skeletal muscle
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Lipid Metabolism
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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 isopreneB. cholesterolC. dehydroepiandrosteroneD. vitamin D
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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 is
A.impaired function of apolipoprotein B-100B.inactivation of capillary lipoprotein lipaseC.increased β-oxidation of fatty acidsxD. increased synthesis of glycerol 3-
phosphate22
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 AB.Hexosaminidase AC. Liver phosphorylasexD. Sphingomyelinase
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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 acidB.7-dehydrocholesterol from cholesterolC. mevalonate from HMG CoAxD. pregnenolone from cholesterolE. progesterone from pregnenolone
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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 child’s primary energy source?
A.Branched-chain amino acidsB.Fatty acidsC.FructosexD. GlucoseE.Ketone bodies
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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.CardiolipinB.CeramidexC. Dipalmitoyl phosphatidylcholineD.GangliosideE. Sphingomyelin
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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 patient?
xA. 11β-HydroxylaseB.17α-HydroxylaseC. 18-HydroxylaseD.21-Hydroxylase
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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.11β-HydroxylasexB. 17α-HydroxylaseC. 18-HydroxylaseD.21-Hydroxylase
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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 lipase+Decreased hormone-sensitive lipase
B.Decreased capillary lipoprotein lipase+Increased hormone-sensitive lipase
xC. Increased capillary lipoprotein lipase+Decreased hormone-sensitive lipase
D.Increased capillary lipoprotein lipase+Increased hormone-sensitive lipase
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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 enzyme?
A.AromataseB.17α-HydroxylaseC. 21-HydroxylaseD.OxidoreductasexE. 5α-Reductase
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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)
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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-IIC. Deficient levels of apolipoprotein ED.Deficient levels of capillary lipoprotein lipasexE. Deficient levels of low-density-lipoprotein
(LDL) receptors32
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/dLSerum high-density lipoprotein cholesterol: 25 mg/dLSerum 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 chylomicronsB. Increased level of chylomicrons and low-density lipoproteins (LDL)C. Increased level of chylomicrons and very-low-density lipoproteins
(VLDL)D. Increased level of LDLE. Increased level of VLDL
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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 activityB.protein kinase A activityC.hormone-sensitive lipase activityxD. lipoprotein lipase activity
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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 man’s 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 vitamins?
A NiacinB.Ascorbic acidC. Vitamin AxD. Vitamin DE. Vitamin K
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Amino Acids and Nitrogen Metabolism
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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 deaminaseB.Hypoxanthine-guanine
phosphoribosyltransferase (HGPRT)C. Orotate phosphoribosyl transferaseD.Xanthine oxidase
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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 acidsxB. Metabolism of branched-chain amino
acidsC.Metabolism of sulfur-containing amino acidsD. One-carbon transfer reactionsE.Transformation of carbohydrates to amino
acids 38
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 achievedB.become negativeC.become positiveD. progress from a negative state to
equilibriumE.progress from a positive state to equilibrium
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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.ArgininexB. AspartateC.GlutamateD. GlutamineE.Glycine
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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.ArginaseB.Argininosuccinate lyaseC.Argininosuccinate synthetasexD. Carbamoyl phosphate synthetase IE.Ornithine carbamoyltransferase
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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.GalactosemiaB.Maple syrup urine diseaseC.Niemann-Pick diseasexD. Phenylketonuria (PKU)E.Wilson disease
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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 ferritinB.Decreased zinc RBC protoporphyrinC. Increased hemoglobin A2 (HbA2 ) and
hemoglobin F (HbF)xD. Increased urinary δ-aminolevulinic acid
(ALA) 43
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 deaminasexB. Hypoxanthine-guanine
phosphoribosyltransferase (HGPRT)C. Phosphoribosylpyrophosphate synthaseD.Thymidine kinaseE. Xanthine oxidase
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40. A 1-year-old boy has a history of recurrent bacterial and fungal infections. Serum protein electrophoresis shows a flat γ-globulin region. Further testing shows increased concentrations of dATP in white blood cells. What is the most likely diagnosis?
xA. Adenosine deaminase deficiencyB.Bruton agammaglobulinemiaC.Lesch-Nyhan syndromeD. OroticaciduriaE.Purine nucleoside phosphorylase deficiency
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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.ArginaseB.Carbamoyl phosphate synthetase IIxC. Ornithine transcarbamoylaseD. Serine hydroxymethyltransferase
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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 liverB.Increases synthesis of vitamin D in the skinC.Metabolizes bilirubin to biliverdinxD. Oxidizes bilirubin to a water-soluble
form47
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. HemoglobinB. MyoglobinxC.PorphobilinD. UrobilinE. Uroporphyrin I
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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 bloodB.Decreased β-oxidation of fatty acidsxC. Decreased synthesis of apolipoproteinsD.Increased intake of fatty foodE. Increased synthesis of fatty acids
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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 fluidsxB. allopurinolC. ciprofloxacinD. lithotripsy E. hydrochlorothiazides
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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 dehydrogenaseB.Methylmalonyl CoA mutaseC. Glutathione reductasexD. δ-aminolevulinic acid synthaseE. Methemoglobin reductase
51
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 HemeB. UrobilinC. PorphobilinxD. Uroporphyrin I 52
Molecular biology Proteins, Enzymes, and Misc Topics
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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 fibrillinB.α-l-iduronidasexC. type I collagenD. type III collagenE.Elastin
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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 myxedema?
A Chondroitin sulfatexB. Dermatan sulfateC. HeparinD.Hyaluronic acidE. Keratan sulfate I
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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 fibrosisB.Duchenne muscular dystrophyxC. Huntington diseaseD.Metachromatic leukodystrophyE. Parkinson disease
56
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 proteinB.Growth factorC.Growth factor receptorD. Nuclear transcription factor
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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 patient’s condition?
A.Blood glucose (fasting)B.Blood ketonesxC. Hemoglobin A1c concentrationD. Serum C-peptide
58
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 strandsB.Defects in DNA repair enzymesC.Point mutations resulting in stop codonsxD. Pyrimidine dimers resulting in distortion
of the DNA helix 59
54. A 3-year-old black girl is brought to a physician’s 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 girl’s 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 β-globin DNA, and a single 234-bp band is diagnostic for sickle cell anemia, what is the most likely diagnosis?
A. Further studies are necessaryB. Results of blood studies are normalC. Sickle cell diseasexD. Sickle cell traitE. β-Thalassemia minor
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• 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. ablB. brcalC. c-mycD. p53E. Rb
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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.EndonucleaseB.ExonucleaseC. HelicaseD.LigasexE. Topoisomerase I
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57. The parents of a 2-year-old child bring their son to the pediatrician’s 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 repairB. DNA replicationC. mRNA splicingD. Protein translationE. RNA transcription
63
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 excisionB.DepurinationC. Nucleotide excisionxD. Postreplication mismatchE. Recombinational
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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 gel?
A. DNA of at least one parent has no 0.5 fragmentB. DNA of at least one parent has neither 0.2 nor 0.3 kb fragmentsxC.DNA of each parent separates into 0.2, 0.3, and 0.5 kb fragmentsD. Maternal DNA migrates as a single 0.5 kb fragmentE. Paternal DNA migrates as a single 0.5 kb fragment
65
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 deaminaseB.Hypoxanthine-guanine
phosphoribosyltransferase (HGPRT)C. Phosphoribosylpyrophosphate (PRPP) synthasexD. Thymidine kinaseE. Xanthine oxidase
66
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 proteinxB. RNA polymeraseC.arabinosyl transferaseD. ribosomal protein
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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 promoterxB. exonC. enhancerD.splice site
68
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 patient’s diarrhea?
A.Activation of a Gq proteinxB. Activation of a Gs proteinC. Inactivation of a Gi proteinD.Inhibition of a Cl¯ channelE. Stimulation of guanylyl cyclase activity
69
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 man’s reaction to alcohol?
A.Gluconeogenesis is inhibited by the abundance of
oxaloacetateB.Gluconeogenesis is inhibited by the abundance of
pyruvateC. Glycogenolysis is inhibited by ethanolD.NADH is used in ethanol metabolismxE. Oxaloacetate and pyruvate are diverted
from the gluconeogenetic pathway 70
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 gumsB.dementiaC. glossitisxD. lactic acidosisE. nystagmus
71
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 fragmentsB. Formation of pro-α-chainsC. Glycosylation of side-chain residuesxD. Hydroxylation of proline and lysine side-chainsE. Triple helix assembly of procollagen
72
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 reductaseB.Intestinal conjugaseC.Production of intrinsic factorD. Reabsorption of folate
73
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 gumsB.Hemolytic anemiaxC. Impaired night visionD.OsteomalaciaE. Pain in the long bones
74
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 increased?
A. blood sodiumB. blood lactateC. blood pHD. serum bicarbonatexE. anion gap
75
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 acyltransferaseB.Citrate synthasexC. GlucokinaseD.Glucose-6-phosphataseE. HMG-CoA synthase
76
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 patient’s breath?
A. Acetyl-CoA carboxylaseB. Citrate lyaseC. HMG-CoA reductasexD. HMG-CoA synthaseE. Pyruvate dehydrogenase
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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 AB.α-GlucosidaseC. Hexosaminidase AD.Muscle phosphorylaseE. Sphingomyelinase
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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 VIxB. Medium-chain acyl CoA dehydrogenase
deficiencyC.Pyruvate carboxylase deficiencyD. Thiamine deficiency
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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 synthaseB. Decreased level of dihydrofolate reductaseC. Decreased level of thymidylate synthetasexD. Decreased serum folateE. Decreased serum vitamin B12 80
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 patient’s tissues?
xA. Decreased arterial pHB.Decreased red blood cell 2,3-
bisphosphoglycerate (2,3-BPG)C.Decreased temperatureD. Hyperventilation
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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 amplificationxB. Mannose 6-phosphate attachmentC.Nuclear localization signalD. Transferrin receptor mRNA
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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 lesion?
A.Chondroitin sulfatexB. Dermatan sulfateC.Heparan sulfateD. Hyaluronic acidE.Keratan sulfate
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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-linkingB.defective collagen fiber synthesisC. defective α-keratin synthesisxD. increased neutrophil elastaseE. mutated elastin protein
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79. A 3-year-old male with nephrotic syndrome has a urine protein level >4 g/day. Physical examination reveals generalized edema and ascites. What best describes the effect on calcium in his serum?
A.Decreased ionized calciumxB. Decreased total calciumC.Normal total calciumD. Increased ionized calcium
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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 deficiencyB. carbon monoxide poisoningxC. methemoglobinemiaD. iron deficiency anemia
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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 transferrinB.ceruloplasminC.ferritinD. haptoglobinE.albumin
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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 structurexB. secondary structureC. tertiary structureD.quaternary structure
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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 ferritinB.Decreased zinc RBC protoporphyrinC. Increased hemoglobin A2 (HbA2) and
hemoglobin F (HbF) xD. Increased urinary δ-aminolevulinic acid
(ALA) 89
