Step 1 Biochemistry Review
John W. Pelley, PhD
john.pelley@ttuhsc.edu
www.ttuhsc.edu/SOM/success/
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
2
Carbohydrate Metabolism
3
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 chain
B. Defect in β-globin chain synthesis
xC. Deficiency of glucose-6-phosphate
dehydrogenase (G6PD)
D.Inhibition of pyruvate kinase
E. Reduced dietary iron absorption
4
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-phosphatase
C. α-Glucosidase
D.Liver phosphorylase
xE. Phosphofructokinase (PFK)
5
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 B
B.Galactose-1-phosphate uridyltransferase
C.Glucose-6-phosphatase
xD. Glucosyl (4:6) transferase
E. Liver phosphorylase
6
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 enzyme
xB. Debranching enzyme
C. Glucose-6-phosphatase
D.α-Glucosidase
E. Liver phosphorylase
7
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. α-l-Iduronidase
D. Phosphotransferase
E. Sphingomyelinase
8
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. Epinephrine
xC. Glucagon
D. Growth hormone
E. Thyroxine
9
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
10
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
11
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
12
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 activity
B.iron deficiency
C.folate deficiency
D. reduced concentrations of ATP
E. 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 Ethanol
xB. Lactic acid
C.Chylomicrons
D. Acetate
14
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
15
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
16
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
17
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 gap
B. electron transport chain
C. Na+/K+ATPase
D.citric acid cycle activity
E. oxidative phosphorylation
18
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
kidney
B. spleen
C. heart
D. brain
E. skeletal muscle
19
Lipid Metabolism
20
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
21
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-100
B.inactivation of capillary lipoprotein lipase
C.increased β-oxidation of fatty acids
xD. increased synthesis of glycerol 3phosphate
22
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
23
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
24
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 acids
B.Fatty acids
C.Fructose
xD. Glucose
E. Ketone bodies
25
22. A 22-year-old woman with poorly controlled
gestational diabetes delivers a large-forgestational 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
26
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 17ketosteroids. Chromosome analysis shows an XX
genotype. What enzyme involved in adrenal
steroid synthesis is most likely deficient in this
patient?
xA. 11β-Hydroxylase
B. 17α-Hydroxylase
C. 18-Hydroxylase
D.21-Hydroxylase
27
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-Hydroxylase
xB. 17α-Hydroxylase
C. 18-Hydroxylase
D.21-Hydroxylase
28
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
29
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.Aromatase
B. 17α-Hydroxylase
C. 21-Hydroxylase
D.Oxidoreductase
xE. 5α-Reductase
30
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)
31
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 lipase
xE. Deficient levels of low-density-lipoprotein
(LDL) receptors
32
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 mg/dL
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
33
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
34
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 Niacin
B. Ascorbic acid
C. Vitamin A
xD. Vitamin D
E. Vitamin K
35
Amino Acids and Nitrogen Metabolism
36
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
(HGPRT)
C. Orotate phosphoribosyl transferase
D.Xanthine oxidase
37
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
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 achieved
B.become negative
C.become positive
D. progress from a negative state to
equilibrium
E. progress from a positive state to equilibrium
39
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
40
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
41
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
42
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 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 deaminase
xB. Hypoxanthine-guanine
phosphoribosyltransferase (HGPRT)
C. Phosphoribosylpyrophosphate synthase
D.Thymidine kinase
E. Xanthine oxidase
44
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 deficiency
B.Bruton agammaglobulinemia
C.Lesch-Nyhan syndrome
D. Oroticaciduria
E. Purine nucleoside phosphorylase deficiency
45
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
46
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
47
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
48
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 β-oxidation of fatty acids
xC. Decreased synthesis of apolipoproteins
D.Increased intake of fatty food
E. Increased synthesis of fatty acids
49
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
50
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. δ-aminolevulinic acid synthase
E. 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 Heme
B. Urobilin
C. Porphobilin
xD. Uroporphyrin I
52
Molecular biology Proteins,
Enzymes, and Misc Topics
53
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.α-l-iduronidase
xC. type I collagen
D. type III collagen
E. Elastin
54
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 sulfate
xB. Dermatan sulfate
C. Heparin
D.Hyaluronic acid
E. Keratan sulfate I
55
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
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 protein
B.Growth factor
C.Growth factor receptor
D. Nuclear transcription factor
57
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 ketones
xC. Hemoglobin A1c concentration
D. 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 strands
B.Defects in DNA repair enzymes
C.Point mutations resulting in stop codons
xD. 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 necessary
B. Results of blood studies are normal
C. Sickle cell disease
xD.
Sickle cell trait
E. β-Thalassemia minor
60
•
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
61
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
62
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 repair
B. DNA replication
C. mRNA splicing
D. Protein translation
E. 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 excision
B. Depurination
C. Nucleotide excision
xD. Postreplication mismatch
E. Recombinational
64
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 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 fragment
E. 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 deaminase
B. Hypoxanthine-guanine phosphoribosyltransferase
(HGPRT)
C. Phosphoribosylpyrophosphate (PRPP) synthase
xD. Thymidine kinase
E. 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 protein
xB. RNA polymerase
C.arabinosyl transferase
D. ribosomal protein
67
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
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 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
69
64. After exercising strenuously for 1 hour, a 23year-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
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
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 gums
B. dementia
C. glossitis
xD. lactic acidosis
E. 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 fragments
B. Formation of pro-α-chains
C. Glycosylation of side-chain residues
xD. Hydroxylation of proline and lysine side-chains
E. 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 reductase
B.Intestinal conjugase
C.Production of intrinsic factor
D. 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 gums
B. Hemolytic anemia
xC. Impaired night vision
D.Osteomalacia
E. 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 sodium
B. blood lactate
C. blood pH
D. serum bicarbonate
xE. 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 acyltransferase
B. Citrate synthase
xC. Glucokinase
D.Glucose-6-phosphatase
E. 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 carboxylase
B. Citrate lyase
C. HMG-CoA reductase
xD. HMG-CoA synthase
E. Pyruvate dehydrogenase
77
72. During a physical examination of a 24-yearold man who is mentally retarded, the physician
notices clumsiness and spasticity of the patient's
limbs, emotional lability, and decreased visualspatial 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. α-Glucosidase
C. Hexosaminidase A
D.Muscle phosphorylase
E. Sphingomyelinase
78
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
deficiency
C.Pyruvate carboxylase deficiency
D. Thiamine deficiency
79
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
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 pH
B.Decreased red blood cell 2,3bisphosphoglycerate (2,3-BPG)
C.Decreased temperature
D. Hyperventilation
81
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
82
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 sulfate
xB. Dermatan sulfate
C.Heparan sulfate
D. Hyaluronic acid
E. Keratan sulfate
83
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 α-keratin synthesis
xD. increased neutrophil elastase
E. mutated elastin protein
84
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 calcium
xB. Decreased total calcium
C.Normal total calcium
D. Increased ionized calcium
85
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
86
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
87
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
88
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 δ-aminolevulinic acid (ALA)
89