Recent questions tagged usmle

by admin (2.6k points) in Biochemistry asked Sep 15

A 15-year-old boy presents with prolonged fa- tigue and mild jaundice following a serious infection. Blood tests reveal hemoglobin of 10.5 g/dL and an elevated reticulocyte count. A peripheral blood smear reveals Heinz bodies. Which of the following best describes the nor- mal action associated with this patient’s meta- bolic defect?

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by admin (2.6k points) in Biochemistry asked Sep 15

Hemoglobin consists of four polypeptide sub- units: two a subunits and two b subunits. The arrangement of these subunits shifts between a taut and relaxed conformation, resulting in changes in hemoglobin’s oxygen affinity. At a given partial pressure of oxygen, which of the following will decrease hemoglobin’s affinity for oxygen?

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by admin (2.6k points) in Biochemistry asked Sep 15

A 6-year-old boy is brought to his pediatrician’s office by his parents, who report that the child has been unusually thirsty for the past week. He also has increased urinary frequency and has wet the bed three times in the past two weeks. A random blood glucose level is 215 mg/dL. The pediatrician suspects that the child has type 1 diabetes mellitus caused by autoimmune destruction of insulin-producing pancreatic b cells. Which of the following is the transporter for glucose to enter pancreatic b cells?

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by admin (2.6k points) in Biochemistry asked Sep 15

At a routine check-up, a 7-year-old boy is found to have osteoporosis. The patient is tall and thin with pale skin, fair hair, and flushed

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by admin (2.6k points) in Biochemistry asked Sep 15

A 53-year-old man presents to his physician, because he has blood in his urine and some low back pain. A gross specimen of kidneys from a patient with the same condition is shown in the image. Which of the following also is associated with this disorder?

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by admin (2.6k points) in Biochemistry asked Sep 15

A 59-year-old woman with history of morbid obesity, hypercholesterolemia, and diabetes mellitus presents to the emergency depart- ment with complaints of substernal chest pain lasting two hours. An ECG reveals ST eleva- tions in the lateral leads. The troponin level at admission is extremely elevated, and a cre- atine kinase-myocardial bound test is pend- ing. Which of the following is a key cell me- diator in the pathogenesis of an atherosclerotic plaque?

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by admin (2.6k points) in Biochemistry asked Sep 15

A 30-year-old man is diagnosed with type I fa- milial dyslipidemia. Recent laboratory studies show an elevated triglyceride level but normal LDL and HDL cholesterol levels. Which of the following explains the pathophysiology of this disease?

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by admin (2.6k points) in Biochemistry asked Sep 15

After consumption of a carbohydrate-rich meal, the liver continues to convert glucose to glucose-6-phosphate. The liver’s ability to con- tinue this processing of high levels of glucose is important in minimizing increases in blood glucose after eating. What is the best explana- tion for the liver’s ability to continue this con- version after eating a carbohydrate-rich meal?

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by admin (2.6k points) in Biochemistry asked Sep 15

An 8-month-old boy is brought to the pediatri- cian by his parents because he has recently lost the ability to crawl or hold his toys. On exami- nation the patient is tachypneic and breathing with considerable effort; the liver is palpable five finger widths below the right costal mar-

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by admin (2.6k points) in Biochemistry asked Sep 15

A 5-year-old boy was playing outside during recess when he began to experience difficulty breathing. He was brought to his physician, because his symptoms seemed to be getting worse. On examination, the physician notes that the boy is struggling to breathe and hears diffuse wheezing bilaterally. The boy’s heart rate is 98/min, respiratory rate is 24/min, and oxygen saturation is 90%. His medical history is significant only for seasonal allergies and mild eczema. Which type of medication will alleviate this patient’s respiratory symptoms?

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by admin (2.6k points) in Biochemistry asked Sep 15

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?

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by admin (2.6k points) in Biochemistry asked Sep 15

A 5-day-old boy is brought to the emergency department after a tonic-clonic seizure at home. The infant is the product of a full-term, uneventful pregnancy, and was normal until two days prior to presentation. The mother re- ports irritability and poor feeding at home, and the infant was difficult to rouse this morning before suffering the seizure. On physical ex- amination, the infant is tachypneic to 75/min, has icteric sclerae, and has poor muscle tone throughout. Laboratory studies show the fol- lowing levels: plasma ammonia, 300 μmol/L (normal = 10-40 μmol/L); blood urea nitro- gen, 1.5 mg/dL; and creatinine, 0.4 mg/dL. A plasma amino acid analysis fails to detect citrulline. Urine amino acids demonstrate el- evated orotic acid levels.

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by admin (2.6k points) in Biochemistry asked Sep 15

A 2-year-old boy presents to the pediatrician with fever, facial tenderness, and a green, foul- smelling nasal discharge. The patient is diag- nosed with sinusitis, and the physician notes that 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 finding would this patient be most likely to have?

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by admin (2.6k points) in Biochemistry asked Sep 15

A 65-year-old woman who has been in the hos- pital for three weeks receiving cefotaxime to treat Klebsiella pneumonia develops a urinary tract infection. Urine cultures are positive for Enterococcus faecium. Treatment with vanco- mycin is attempted but is unsuccessful. Which of the following aided in this microorganism’s ability to persist despite vancomycin treat- ment?

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by admin (2.6k points) in Biochemistry asked Sep 15

A 32-year-old woman presents to her physician for the third time in six 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 three 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 per- formed (see image). This woman may have a human leukocyte antigen subtype that also in- creases her risk of which disease?

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by admin (2.6k points) in Biochemistry asked Sep 15

A segment of DNA is isolated and added to a mixture of four deoxynucleotides, two specific oligonucleotide sequences, and heat-stable DNA polymerase. The mixture is then heated to denature the DNA, cooled, and reheated in a number of cycles. Which of the following laboratory techniques does this describe?

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by admin (2.6k points) in Biochemistry asked Sep 15

A 52-year-old man with a 12-year history of poorly controlled diabetes mellitus presents to his physician complaining of changes in his vi- sion. Physical examination reveals opacities on the lens of the eye similar to those seen in this image. Which enzyme most likely contributed to this complication?

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by admin (2.6k points) in Biochemistry asked Sep 15

A mother brings her 6-month-old son to the pediatrician. She has noticed that he seems “afraid of light” and, after some Internet re- search, she is concerned that he might be an albino. Laboratory analysis reveals uropor- phyrin in his urine. The child most likely has which of the following conditions?

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by admin (2.6k points) in Biochemistry asked Sep 15

A scientist working in a research laboratory has been examining different agonists of serotonin receptor 1B (5-HT1B), a G-protein-coupled re- ceptor. Compound A has a much higher affin- ity for 5-HT1B than compound B. Both com- pounds have a higher affinity for the receptor than serotonin. Which of the following de- scribes the relationship between compound A and compound B when considering the guan- ine-nucleotide exchange activity of 5-HT1B?

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by admin (2.6k points) in Biochemistry asked Sep 15

As increased intracellular calcium is detrimen- tal to the cell, calcium homeostasis is tightly regulated both across the cell membrane and within the cell via sequestration in the en- doplasmic reticulum and mitochondria. In which of the following ways does increased intracellular calcium concentration cause the most cell damage?

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