Biochemistry USMLE practice questions
thrombocytopenia - deficiency of platelets in the blood. This causes bleeding into the
tissues, bruising, and slow blood clotting after injury.
A 16 year old boy presented to a doctor by his mother for the injury which he had
recently during cycle riding. On examination doctor noticed the loose, overly-flexible
joints, smooth or stretchy, easily-bruised skin and abnormal wound healing and scar
formation. This is the characteristic feature of the disorder known as - Ehlers-Danlos
syndrome
A 67-year-old man has a restricted diet that includes no fresh citrus fruits or leafy green
vegetables. His teeth are loose and his gums bleed easily. This patient's disorder most
likely results from a defect in collagen synthesis that involves which of the following
amino acids? - Hydroxyproline
N-terminal and C -terminal polypeptides of collagen are cleaved in - Extracellular space
A 15 year old boy visited the physician with the complaints of joint pain, bleeding of the
gums and loosening of the teeth. This is due to the defect in the post translational
modification of collagen molecule. This problem is corrected by supplying which
compound in the diet of the patient? - Ascorbic acid
A 40 year old woman, cigarette smoker, complained about shortness of breath and
chronic fatigue. Which one of the following most likely explains the patient's pulmonary
symptoms? - Deficiency of α1- Antitrypsin
Cross-linking of collagen to form mature collagen fibrils occurs at which of the following
sites? - Extracellular space
Individuals who are habitual and chronic smokers are likely to have a functional
deficiency of alpha 1 antitrypsin. This can cause pulmonary emphysema based on
accelerated degradation of - Elastin
Some forms of Ehlers-Danlos syndrome are characterized by abnormally elastic skin.
This is due to defective formation and function of - Collagen
The enzyme that catalyzes the cross-linking of the side chains of four lysine residues to
form desmosine is - Lysyl oxidase
A 60 year old man who lives alone came to the clinic with complaints of bleeding gums.
After investigation he was found to have vitamin C deficiency, which is required for
which stage of collagen biosynthesis? - Hydroxylation of proline and lysine residues,
you need vitamin C during this stage.
,27-year-old woman with epilepsy has been taking phenytoin to control her seizures. She
is now pregnant, and her physician is considering changing her medication to prevent
potential bleeding episodes in the infant. What biochemical activity might be deficient in
the infant if her medication is continued? - γ-Carboxylation of glutamate
39 year old male farmer is brought to the emergency department. Three hours
previously he had been spraying fields with an insecticide called Fenoxycarb. He did not
use any respiratory protection and has inhaled the vapour. He shows rippling of the
muscles under the skin, blurred vision and complains of chest tightness. He is unable to
walk. Fenoxycarb is a non-competitive inhibitor of the enzyme acetylcholinesterase, an
important mediator of neurotransmitter action. Which of the following best describes the
effect of this poison on the enzyme? - Vmax is reduced, Km is unaltered (Non
competitive inhibitor)
The conversion of dihydroxyacetone (DHAP) to glyceraldehyde-3-phosphate (GAP) is a
freely reversible reaction with an equilibrium constant close to 1. The interconversion is
catalyzed by the enzyme triose phosphate isomerase. The presence of this enzyme in a
solution of glyceraldehyde-3-phosphate will have the following effect compared with an
identical solution with no enzyme. - Decrease the time taken to reach equilibrium.
Which of the following statement is true of thrombin? - It stimulates platelets
aggregation
The number of substrate molecules converted to product by one molecule of enzyme
each second is known as the - turnover number
Allosteric postive homo-tropic effector -
Psoriasis is a chronic, non-contagious autoimmune disease that affects the skin and
joints. It commonly causes red, scaly patches to appear on the skin. Which forms of
retinoids is useful in the treatment of this condition? - Ratinoic acid
Riboflavin plays a key role in energy metabolism and is required for the metabolism of
fats, carbohydrates and proteins. Deficiency features of the vitamin includes cracked
and red lips, inflammation of the lining of mouth and tongue, mouth ulcers, cracks at the
corners of the mouth. In which one of the following reactions its coenzyme is required? -
Acyl CoA -------> 2- trans- Enoyl CoA
20 year old medical student met an accident and suffered from multiple injuries all over
the body with the bone fracture. Your surgeon colleague prefers to supplement patients
with ascorbic acid after surgery. The doctor trying to optimize which one of the following
process? - The hydroxylation of proline in tropocollagen=helps with the healing of the
bone fracture.
, A 16 month-old girl of middle eastern parents is admitted with growth retardation. Her
long bones show demineralization with bowing of both the arms and the legs. The
patient avoided dairy products due to a lactose intolerance and her diet was composed
primarily of eggs, potatoes, and other baked goods. When she was taken outside by her
mother they were both heavily clad so as to not expose any of their skin, effectively
blocking exposure to the sun. What is the most likely diagnosis from the choices below?
- Vitamin D deficiency, not exposed to the sun.
A 43 year old Asian male presents at an outpatient department with steatorrhea. Which
of the following vitamin absorptions would be affected by this? - Vitamin E
25 year old lady had a severe vomiting and morning sickness and visited a
gynecologist. Upon examination doctor told her the good news that pregnancy test is
positive and prescribed the multivitamin tablets. Which one of the following vitamin to
reduce the risk of a pregnancy affected by spina bifida or other neural tube defects? -
Folic acid
A 54 year-old male presents in the clinics with neurological deficits such as global
confusion, apathy and disorientation. He has a 20 year of alcohol abuse. His symptoms
are typically associated with the dietary deficiency or impaired absorption of which of
the following vitamins? - Vitamin B1 =fixes neurodegenerative problems, and eye sights.
Your patient has been diagnosed with pernicious anemia. Since part of this syndrome
involves megaloblastic anemia with neuropsychiatric problems (myelopathy). You
decide to treat the patient with folate supplements. Which of the following do you expect
to happen? - Folate will successfully treat the megaloblastic anemia, but not the
myelopathy.
position of equilibrium in the graph -
A particular cytochrome enzyme normally has oxidoeductase activity and contains an
iron-based heme group. The enzyme is translated and folded before the heme group is
incorporated. An individual who has an iron malabsorption problem will produce only the
protein without the heme. Such a protein is referred to as a(n) - apoenzyme
A 40 year old woman primarily subsists on fast foods, hotdogs and diet drinks. Primary
examination reveals bleeding gums, loosening of the teeth and perifollicular
hemorrhages. The mechanism of vascular instability in this patient is most closely
associated with deficiency of which of the following vitamins? - Vitamin C
A 38 year old man with 8 year history of alcohol abuse present to a family doctor with a
complaint of diminished taste and smell. Physical examination reveals rash across his
face and neck. In addition poor healing of skin incision site on the back of his right hand.
Which of the trace element is most likely deficient? - Zink
thrombocytopenia - deficiency of platelets in the blood. This causes bleeding into the
tissues, bruising, and slow blood clotting after injury.
A 16 year old boy presented to a doctor by his mother for the injury which he had
recently during cycle riding. On examination doctor noticed the loose, overly-flexible
joints, smooth or stretchy, easily-bruised skin and abnormal wound healing and scar
formation. This is the characteristic feature of the disorder known as - Ehlers-Danlos
syndrome
A 67-year-old man has a restricted diet that includes no fresh citrus fruits or leafy green
vegetables. His teeth are loose and his gums bleed easily. This patient's disorder most
likely results from a defect in collagen synthesis that involves which of the following
amino acids? - Hydroxyproline
N-terminal and C -terminal polypeptides of collagen are cleaved in - Extracellular space
A 15 year old boy visited the physician with the complaints of joint pain, bleeding of the
gums and loosening of the teeth. This is due to the defect in the post translational
modification of collagen molecule. This problem is corrected by supplying which
compound in the diet of the patient? - Ascorbic acid
A 40 year old woman, cigarette smoker, complained about shortness of breath and
chronic fatigue. Which one of the following most likely explains the patient's pulmonary
symptoms? - Deficiency of α1- Antitrypsin
Cross-linking of collagen to form mature collagen fibrils occurs at which of the following
sites? - Extracellular space
Individuals who are habitual and chronic smokers are likely to have a functional
deficiency of alpha 1 antitrypsin. This can cause pulmonary emphysema based on
accelerated degradation of - Elastin
Some forms of Ehlers-Danlos syndrome are characterized by abnormally elastic skin.
This is due to defective formation and function of - Collagen
The enzyme that catalyzes the cross-linking of the side chains of four lysine residues to
form desmosine is - Lysyl oxidase
A 60 year old man who lives alone came to the clinic with complaints of bleeding gums.
After investigation he was found to have vitamin C deficiency, which is required for
which stage of collagen biosynthesis? - Hydroxylation of proline and lysine residues,
you need vitamin C during this stage.
,27-year-old woman with epilepsy has been taking phenytoin to control her seizures. She
is now pregnant, and her physician is considering changing her medication to prevent
potential bleeding episodes in the infant. What biochemical activity might be deficient in
the infant if her medication is continued? - γ-Carboxylation of glutamate
39 year old male farmer is brought to the emergency department. Three hours
previously he had been spraying fields with an insecticide called Fenoxycarb. He did not
use any respiratory protection and has inhaled the vapour. He shows rippling of the
muscles under the skin, blurred vision and complains of chest tightness. He is unable to
walk. Fenoxycarb is a non-competitive inhibitor of the enzyme acetylcholinesterase, an
important mediator of neurotransmitter action. Which of the following best describes the
effect of this poison on the enzyme? - Vmax is reduced, Km is unaltered (Non
competitive inhibitor)
The conversion of dihydroxyacetone (DHAP) to glyceraldehyde-3-phosphate (GAP) is a
freely reversible reaction with an equilibrium constant close to 1. The interconversion is
catalyzed by the enzyme triose phosphate isomerase. The presence of this enzyme in a
solution of glyceraldehyde-3-phosphate will have the following effect compared with an
identical solution with no enzyme. - Decrease the time taken to reach equilibrium.
Which of the following statement is true of thrombin? - It stimulates platelets
aggregation
The number of substrate molecules converted to product by one molecule of enzyme
each second is known as the - turnover number
Allosteric postive homo-tropic effector -
Psoriasis is a chronic, non-contagious autoimmune disease that affects the skin and
joints. It commonly causes red, scaly patches to appear on the skin. Which forms of
retinoids is useful in the treatment of this condition? - Ratinoic acid
Riboflavin plays a key role in energy metabolism and is required for the metabolism of
fats, carbohydrates and proteins. Deficiency features of the vitamin includes cracked
and red lips, inflammation of the lining of mouth and tongue, mouth ulcers, cracks at the
corners of the mouth. In which one of the following reactions its coenzyme is required? -
Acyl CoA -------> 2- trans- Enoyl CoA
20 year old medical student met an accident and suffered from multiple injuries all over
the body with the bone fracture. Your surgeon colleague prefers to supplement patients
with ascorbic acid after surgery. The doctor trying to optimize which one of the following
process? - The hydroxylation of proline in tropocollagen=helps with the healing of the
bone fracture.
, A 16 month-old girl of middle eastern parents is admitted with growth retardation. Her
long bones show demineralization with bowing of both the arms and the legs. The
patient avoided dairy products due to a lactose intolerance and her diet was composed
primarily of eggs, potatoes, and other baked goods. When she was taken outside by her
mother they were both heavily clad so as to not expose any of their skin, effectively
blocking exposure to the sun. What is the most likely diagnosis from the choices below?
- Vitamin D deficiency, not exposed to the sun.
A 43 year old Asian male presents at an outpatient department with steatorrhea. Which
of the following vitamin absorptions would be affected by this? - Vitamin E
25 year old lady had a severe vomiting and morning sickness and visited a
gynecologist. Upon examination doctor told her the good news that pregnancy test is
positive and prescribed the multivitamin tablets. Which one of the following vitamin to
reduce the risk of a pregnancy affected by spina bifida or other neural tube defects? -
Folic acid
A 54 year-old male presents in the clinics with neurological deficits such as global
confusion, apathy and disorientation. He has a 20 year of alcohol abuse. His symptoms
are typically associated with the dietary deficiency or impaired absorption of which of
the following vitamins? - Vitamin B1 =fixes neurodegenerative problems, and eye sights.
Your patient has been diagnosed with pernicious anemia. Since part of this syndrome
involves megaloblastic anemia with neuropsychiatric problems (myelopathy). You
decide to treat the patient with folate supplements. Which of the following do you expect
to happen? - Folate will successfully treat the megaloblastic anemia, but not the
myelopathy.
position of equilibrium in the graph -
A particular cytochrome enzyme normally has oxidoeductase activity and contains an
iron-based heme group. The enzyme is translated and folded before the heme group is
incorporated. An individual who has an iron malabsorption problem will produce only the
protein without the heme. Such a protein is referred to as a(n) - apoenzyme
A 40 year old woman primarily subsists on fast foods, hotdogs and diet drinks. Primary
examination reveals bleeding gums, loosening of the teeth and perifollicular
hemorrhages. The mechanism of vascular instability in this patient is most closely
associated with deficiency of which of the following vitamins? - Vitamin C
A 38 year old man with 8 year history of alcohol abuse present to a family doctor with a
complaint of diminished taste and smell. Physical examination reveals rash across his
face and neck. In addition poor healing of skin incision site on the back of his right hand.
Which of the trace element is most likely deficient? - Zink
