United State Medical Licensing Examination (Step 1) Set 10

A 4-year-old patient is presented in the pediatric clinic with microcytic anemia. An analysis of his blood by nondenaturing electrophoresis reveals the following composition of hemoglobin isoforms: HbF = 75%, HbA = 23%, HbA2 = 2%, and HbS = 0%. Using these data, is it possible to determine that the infant is most likely homozygous for which of the following?

Hepatocytes deliver ketone bodies to the circulation because they lack which of the following enzymes?

 

Which of the following statements reflects the process by which the telomeric ends of chromosomes are replicated?

In carrying out an assay using cultured hepatocytes, you find that addition of hemin (Fe3+ heme) does not have the expected consequence of reduced protoporphyrin IX synthesis. This result suggests that your hepatocytes harbor a mutant form of one of the heme-regulated enzymes of porphyrin biosynthesis. Which of the following represents the likely enzyme?

Hemochromatosis, a disorder that is the result of excess iron accumulation, is caused by deficiencies in which of the following proteins?

Amother has brought her 3-month-old baby to the pediatrician and indicates that the infant is lethargic and has poor suckling and seems uninterested in eating. In addition, the mother notes that the baby's diapers often smell like burnt sugar. This infant likely has a defect in which of the following enzymes?

Amale infant, delivered at 38 weeks' gestation, presents with severe bowing of long bones, blue sclera, and craniotabes at birth. Radiographs show severe generalized osteoporosis, broad and crumpled long bones, beading ribs, and a poorly mineralized skull. Histologic examination of the long bones revealed the trabecula of the calcified cartilage with an abnormally thin layer of osteoid, and the bony trabeculae are thin and basophilic. The symptoms observed in the infant are characteristic of which disease?

Obesity, genetic profile, and aging all contribute to the development of Type II diabetes. Of the following, which is the most important additive factor for these three conditions in the development of Type II diabetes?

A2-month-old infant suffering from increased vomiting and diarrhea is seen in the hospital and observed to have significant abdominal distention due to hepatosplenomegaly. Unfortunately, the infant does not survive. Autopsy reveals calcification of the adrenals and massive accumulation of cholesteryl esters and triglycerides in most tissues. Analysis of enzyme activity in fibroblasts and lymphocytes demonstrates a significant acid lipase (cholesteryl ester hydrolase) deficiency. These clinical findings are indicative of which of the following disorders?

As a hypothetical approach to treating the hyperglycemia associated with Type II diabetes, a drug firm proposes to develop an inhibitor of liver glycogen phosphorylase. What is the biochemical rationale for this approach to inducing hypoglycemia?