USMLE Biochemistry Mcqs
USMLE Step 1, Biochemistry Multiple Choice Questions, (Mcqs) Page 2. Mcqs are obtaining from reliable sources, Uworld and others.
Prepare free your USMLE Step 1 Exam.
Pages: 1 2 3
Quiz-summary
0 of 10 questions completed
Questions:
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
Information
USMLE Biochemistry Free quiz
You have already completed the quiz before. Hence you can not start it again.
Quiz is loading...
You must sign in or sign up to start the quiz.
You have to finish following quiz, to start this quiz:
Results
0 of 10 questions answered correctly
Your time:
Time has elapsed
You have reached 0 of 0 points, (0)
Categories
- Not categorized 0%
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
- Answered
- Review
- Question 1 of 10
1. Question
An 18-year-old woman presents to the emergency department with acute onset of severe abdominal pain. She says she had a similar attack
1 year earlier after taking some barbiturates. At that time she underwent an exploratory laparotomy, which revealed nothing. The
patient no longer takes barbiturates but recently started an extremely low-carbohydrate and low-calorie diet. She has a temperature of
37°C (98.6°F), a respiratory rate of 16/min, and a blood pressure of 128/83 mm Hg. Her WBC count is normal. Laboratory studies reveal a sodium level of 127 mEq/L, and urinalysis shows increased porphobilinogen levels.The physician tells the patient that she has agenetic condition involving her RBCs. Whatcongenital disorder did the physician most likely tell the patient she has?CorrectThe correct answer is A. Acute intermittent
porphyria (AIP) is a blood disorder caused by a
defi ciency of uroporphyrinogen I synthetase.
δ-Aminolevulinic acid and porphobilinogen
are found in the urine. Patients often present
with hyponatremia and recurrent episodes of
abdominal pain and can even develop neuropsychiatric
problems. Barbiturates (among
other drugs) and starvation diets can precipitate
attacks. Patients with AIP do not have the
cutaneous photosensitivity seen in other porphyrias.IncorrectThe correct answer is A. Acute intermittent
porphyria (AIP) is a blood disorder caused by a
defi ciency of uroporphyrinogen I synthetase.
δ-Aminolevulinic acid and porphobilinogen
are found in the urine. Patients often present
with hyponatremia and recurrent episodes of
abdominal pain and can even develop neuropsychiatric
problems. Barbiturates (among
other drugs) and starvation diets can precipitate
attacks. Patients with AIP do not have the
cutaneous photosensitivity seen in other porphyrias. - Question 2 of 10
2. Question
A 48-year-old woman presents to a new physician because of the recent onset of fatigue, arthralgias, discomfort in her right upper quadrant, and polyuria. On physical examination, her skin seems somewhat browner than would be expected. Laboratory tests are remarkable for an elevated glucose level, indications of hemolysis, and increased transferrin saturation. Cardiac testing shows moderate restrictive cardiomyopathy. She mentions that she regularly requires blood transfusions. Which of the following is the cause of this patient’s condition?
CorrectThe correct answer is B. This woman suffers
from β-thalassemia major. Clinically, β-thalassemia
major manifests as severe hemolysis and
ineffective erythropoiesis. These individuals
are transfusion-dependent and frequently develop
iron overload. The consequences of iron
overload due to transfusion dependency or secondary
hemochromatosis are described in the
question stem. These manifestations are due to
iron deposition in various tissues, including the
pancreas, heart, and skin.IncorrectThe correct answer is B. This woman suffers
from β-thalassemia major. Clinically, β-thalassemia
major manifests as severe hemolysis and
ineffective erythropoiesis. These individuals
are transfusion-dependent and frequently develop
iron overload. The consequences of iron
overload due to transfusion dependency or secondary
hemochromatosis are described in the
question stem. These manifestations are due to
iron deposition in various tissues, including the
pancreas, heart, and skin. - Question 3 of 10
3. Question
A 52-year-old man with a 12-year history of poorly controlled diabetes mellitus presents to his physician complaining of changes in his vision. Physical examination reveals opacities on the lens of the eye similar to those seen in the image. Which enzyme most likely contributed to this complication?
CorrectThe correct answer is B. Aldose reductase catalyzes
the breakdown of glucose into sorbitol.
Sorbitol is then metabolized to fructose, a process
that is relatively slow. In patients with hyperglycemia,
as would be present in this patient
with poorly controlled diabetes, sorbitol
accumulation with the cells of the lens leads to
a rise in intracellular osmolality, causing water
movement into the cells. This results in cellular
swelling and osmotic damage. It also leads
to a decrease in intracellular myoinositol, interfering
with cellular metabolism. Swelling of
lens fi ber cells can lead to rupture and cataract
formation (as seen in the image). Inhibition of
aldose reductase could decrease sorbitol accumulation
in the lens and thus prevent cataract
formation. No drug is currently approved to inhibit
aldose reductase, but aldose reductase inhibitors
such as epalrestat and ranirestat are
currently being tested.
IncorrectThe correct answer is B. Aldose reductase catalyzes
the breakdown of glucose into sorbitol.
Sorbitol is then metabolized to fructose, a process
that is relatively slow. In patients with hyperglycemia,
as would be present in this patient
with poorly controlled diabetes, sorbitol
accumulation with the cells of the lens leads to
a rise in intracellular osmolality, causing water
movement into the cells. This results in cellular
swelling and osmotic damage. It also leads
to a decrease in intracellular myoinositol, interfering
with cellular metabolism. Swelling of
lens fi ber cells can lead to rupture and cataract
formation (as seen in the image). Inhibition of
aldose reductase could decrease sorbitol accumulation
in the lens and thus prevent cataract
formation. No drug is currently approved to inhibit
aldose reductase, but aldose reductase inhibitors
such as epalrestat and ranirestat are
currently being tested. - Question 4 of 10
4. Question
Glucose is transported into human cells by two different families of membrane-associated carrier proteins: the glucose transporter facilitators (GLUT) and the sodium-coupled glucose transporters (SGLT). If a patient has a defect in the non-sodium-coupled glucose transporters, which cell line is still able to acquire glucose?
CorrectThe correct answer is B. This patient would
likely have a defect of glucose transporter 1,
which transports glucose across the blood-brain
barrier. A family of glucose transporters (GLUT
1-5) is responsible for cellular uptake in many
cell types. However, enterocytes and nephrons
acquire glucose through cotransport with sodium
ion.IncorrectThe correct answer is B. This patient would
likely have a defect of glucose transporter 1,
which transports glucose across the blood-brain
barrier. A family of glucose transporters (GLUT
1-5) is responsible for cellular uptake in many
cell types. However, enterocytes and nephrons
acquire glucose through cotransport with sodium
ion. - Question 5 of 10
5. Question
A 31-year-old white woman is trying to get pregnant. She has a niece who suffers from a genetic disease characterized by recurrent respiratory infections and pancreatic failure. She would like to assess her chances of having a child with this disease. Which of the following laboratory techniques could be used to determine if this woman and/or her husband is a carrier of the mutant gene?
CorrectThe correct answer is D. PCR and sequencing
can be used to determine if this woman and/or
her husband is a carrier of the cystic fi brosis
gene, the most common single-gene mutation
in white people. This mutation commonly
presents with dysfunction of the lungs, pancreas,
and other organs due to buildup of thick
mucus. PCR is used to amplify the region of
interest, and sequencing is used to see if the
cystic fi brosis mutation is present.IncorrectThe correct answer is D. PCR and sequencing
can be used to determine if this woman and/or
her husband is a carrier of the cystic fi brosis
gene, the most common single-gene mutation
in white people. This mutation commonly
presents with dysfunction of the lungs, pancreas,
and other organs due to buildup of thick
mucus. PCR is used to amplify the region of
interest, and sequencing is used to see if the
cystic fi brosis mutation is present. - Question 6 of 10
6. Question
32-year-old woman presents to her physician for the third time in 6 months. She has been feeling very tired and depressed, and has come to talk about starting antidepressants. She also complains of a 4.5-kg (10-lb) weight gain over the past 3 months. During her physical examination the physician notices that she is wearing a sweater and a coat, despite the room being at a warm temperature. Problems with the thyroid are suspected, and a biopsy is performed (see image). This woman may have a human leukocyte antigen subtype that also increases her risk of which disease?CorrectThe correct answer is B. This woman has
symptoms of Hashimoto’s thyroiditis, an autoimmune
disorder resulting in hypothyroidism
(also known as myxedema), although there
may be a transient hyperthyroidism at the very
onset of disease when follicular rupture occurs.
It is a type IV hypersensitivity associated with
autoantibodies to thyroglobulin, thyroid peroxidase,
and the thyroid-stimulating hormone receptor
itself. The most common presenting
symptoms of Hashimoto’s thyroiditis are those
seen in this patient, as well as constipation and
dry skin. Histologic characteristics include
massive infi ltrates of lymphocytes with germinal
cell formation. Hashimoto’s thyroiditis is
associated with the DR5 human leukocyte antigen
subtype, as is pernicious anemia, a disease
that leads to vitamin B12 defi ciency caused
by atrophic gastritis and destruction of parietal
cells.IncorrectThe correct answer is B. This woman has
symptoms of Hashimoto’s thyroiditis, an autoimmune
disorder resulting in hypothyroidism
(also known as myxedema), although there
may be a transient hyperthyroidism at the very
onset of disease when follicular rupture occurs.
It is a type IV hypersensitivity associated with
autoantibodies to thyroglobulin, thyroid peroxidase,
and the thyroid-stimulating hormone receptor
itself. The most common presenting
symptoms of Hashimoto’s thyroiditis are those
seen in this patient, as well as constipation and
dry skin. Histologic characteristics include
massive infi ltrates of lymphocytes with germinal
cell formation. Hashimoto’s thyroiditis is
associated with the DR5 human leukocyte antigen
subtype, as is pernicious anemia, a disease
that leads to vitamin B12 defi ciency caused
by atrophic gastritis and destruction of parietal
cells. - Question 7 of 10
7. Question
A 65-year-old woman develops a urinary tract infection. Urine cultures are positive for Enterococcus faecium. Treatment with vancomycin is attempted but is unsuccessful. Which of the following molecular changes is responsible for this patient’s vancomycin resistance?
CorrectThe correct answer is A. Vancomycin is an antibiotic
that is effective only in fi ghting grampositive
cocci. It binds tightly to a cell wall precursor
that contains the amino acid sequence
D-ala D-ala and prevents cell wall synthesis. Resistance
to vancomycin is transferred via plasmids
and encodes enzymes that convert D-ala
D-ala to D-ala D-lac, preventing vancomycin
from binding. This type of resistance is much
more common with Enterococcus faecium than
with Enterococcus faecalis.IncorrectThe correct answer is A. Vancomycin is an antibiotic
that is effective only in fi ghting grampositive
cocci. It binds tightly to a cell wall precursor
that contains the amino acid sequence
D-ala D-ala and prevents cell wall synthesis. Resistance
to vancomycin is transferred via plasmids
and encodes enzymes that convert D-ala
D-ala to D-ala D-lac, preventing vancomycin
from binding. This type of resistance is much
more common with Enterococcus faecium than
with Enterococcus faecalis. - Question 8 of 10
8. Question
A 2-year-old boy presents to the pediatrician with fever, facial tenderness, and a green, foulsmelling nasal discharge. The patient is diagnosed with sinusitis, and the physician notesthat he has a history of recurrent episodes of sinusitis. X-ray of the chest is ordered because of the fever; it reveals some dilated bronchi and shows the heart situated on the right side of his body. A congenital disorder is diagnosed. Which other fi nding would this patient be most likely to have?
CorrectThe correct answer is C. Kartagener’s syndrome,
or immotile cilia, is caused by a defect
in dynein that prevents effective movement of
cilia. The full syndrome is characterized by sinusitis,
bronchiectasis, situs inversus, and male
infertility. Cilia play an important role in moving
mucus along the airway and clearing debris;
the absence of this function contributes to the
pulmonary fi ndings of the syndrome. Cilia are
also very important for leukocyte movement and
phagocytosis. Infertility is present in most patients
due to immotile cilia.IncorrectThe correct answer is C. Kartagener’s syndrome,
or immotile cilia, is caused by a defect
in dynein that prevents effective movement of
cilia. The full syndrome is characterized by sinusitis,
bronchiectasis, situs inversus, and male
infertility. Cilia play an important role in moving
mucus along the airway and clearing debris;
the absence of this function contributes to the
pulmonary fi ndings of the syndrome. Cilia are
also very important for leukocyte movement and
phagocytosis. Infertility is present in most patients
due to immotile cilia. - Question 9 of 10
9. Question
A 9-month-old boy is brought to the emergency department after his mother is unable to rouse him. His past medical history is signifi cant for the onset of seizures at the age of 4 months and for a delay in reaching developmental milestones. On examination, the patient is found to have poor muscle tone and an enlarged liver. Laboratory studies show a blood urea nitrogen level of 3.2 mg/dL, a creatinine level of 0.4 mg/ dL, and a serum ammonia level of 300 mg/dL. A plasma amino acid analysis fails to detect citrulline, while his urinary orotic acid level is increased. This patient suffers from a defi ciency of which of the following enzymes?
CorrectThe correct answer is D. This child is suffering
from an inherited form of hyperammonemia
as a result of a defect in ornithine transcarbamoylase.
This enzyme is a component of the
urea cycle that is responsible for combining
carbamoyl phosphate and ornithine to make
citrulline. As a result, the patient has an excess
of ammonia in circulation, which leads to
mental retardation, seizures, and ultimately
death. Some patients with ornithine transcarbamoylase
defi ciency also exhibit a very low
blood urea nitrogen level, but this is not
enough to make a conclusive diagnosis.IncorrectThe correct answer is D. This child is suffering
from an inherited form of hyperammonemia
as a result of a defect in ornithine transcarbamoylase.
This enzyme is a component of the
urea cycle that is responsible for combining
carbamoyl phosphate and ornithine to make
citrulline. As a result, the patient has an excess
of ammonia in circulation, which leads to
mental retardation, seizures, and ultimately
death. Some patients with ornithine transcarbamoylase
defi ciency also exhibit a very low
blood urea nitrogen level, but this is not
enough to make a conclusive diagnosis. - Question 10 of 10
10. Question
A 42-year-old woman presents to her physician with generalized itching. Physical examination reveals scleral icterus. Laboratory tests show: Total bilirubin: 2.7 mg/dL Conjugated bilirubin: 2.4 mg/dL Alkaline phosphatase: 253 U/L Aspartate aminotransferase: 36 U/L Alanine aminotransferase: 40 U/L What is the most likely mechanism underlying this patient’s jaundice?
CorrectThe correct answer is D. This patient has obstructive
jaundice, causing her pruritus and
scleral icterus. In this situation conjugated bilirubin
cannot be excreted, and its levels are therefore elevated in the serum. The unconjugated
bilirubin level, however, is not elevated.
Alkaline phosphatase is usually elevated in
cases of obstructive jaundice.IncorrectThe correct answer is D. This patient has obstructive
jaundice, causing her pruritus and
scleral icterus. In this situation conjugated bilirubin
cannot be excreted, and its levels are therefore elevated in the serum. The unconjugated
bilirubin level, however, is not elevated.
Alkaline phosphatase is usually elevated in
cases of obstructive jaundice.