Metabolism — MCQs

A 5-month-old boy is brought to the pediatrician by his parents, who began noticing that the infant was not able to hold his head upright when sitting or in a prone position. Upon examination, the infant has a musty odor, fair skin with patches of eczema, and blue eyes. The pediatrician orders laboratory tests and prescribes a special diet. Which of the following amino acids becomes essential and must be supplemented in this patient's condition?

A 22-year-old primigravid woman comes to the physician for her initial prenatal visit at 12 weeks' gestation. She has had generalized fatigue and shortness of breath over the past 2 months. She has also had a tingling sensation in her toes for the past month. Three years ago, she was treated for gonorrhea. She follows a strict vegan diet since the age of 13 years. Her temperature is 37°C (98.6°F), pulse is 111/min, and blood pressure is 122/80 mm Hg. Examination shows pale conjunctivae and a shiny tongue. Muscle tone and strength is normal. Deep tendon reflexes are 2+ bilaterally. Sensation to vibration and position is decreased over the upper and lower extremities. When asked to stand, hold her arms in front of her, and close her eyes, she loses her balance and takes a step backward. Which of the following is most likely to have prevented this patient's condition?

A 2-month-old Middle Eastern female infant from a consanguinous marriage presents with seizures, anorexia, failure to thrive, developmental delay, and vomiting and fatigue after eating. Blood work demonstrated levels of methylmalonic acid nearly 500 times normal levels. A carbon-14 propionate incorporation assay was performed on the fibroblasts of the patient and compared to a healthy, normal individual. Little to none of the radiolabeled carbons of the propionate appeared in any of the intermediates of the Krebs cycle. Which of the following reactions is not taking place in this individual?

A 10-year-old boy is brought into your clinic by his mother for sunburns that have not been healing. The mother states that he easily gets sunburned. The mother admits she gave birth to him at home and has never taken him to see a doctor. The patient walks with a wide stance gait and appears unstable on his feet. He has an extensive erythematous, scaling, hyperkeratotic rash on his face, neck, arms and legs. After extensive workup, the patient is found to have a genetic disorder that results in defective absorption of an important vitamin. Which of the following is likely to be low if measured?

An investigator is studying severely ill patients who experience hypoglycemia and ketonuria during times of fasting. The investigator determines that during these episodes, amino acids liberated from muscle proteins are metabolized to serve as substrates for gluconeogenesis. Nitrogen from this process is transported to the liver primarily in the form of which of the following molecules?

A 4-year-old boy is brought to the physician because of a rash and difficulty swallowing. His family emigrated from Nigeria 2 months ago. Examination shows an erythematous rash with fine yellow scales on his eyebrows and nasolabial folds. Oral examination shows an erythematous throat and swollen tongue. There is peeling and fissures of the skin at the corners of the mouth and cracking of the lips. His hemoglobin concentration is 9.6 g/dL; mean corpuscular volume is 89 μm3. Erythrocyte glutathione reductase assay shows an increased activity coefficient. This patient is most likely deficient in a vitamin that is a precursor to which of the following molecules?

An 18-month-old boy is brought in to the pediatrician by his mother for concerns that her child is becoming more and more yellow over the past two days. She additionally states that the boy has been getting over a stomach flu and has not been able to keep down any food. The boy does not have a history of neonatal jaundice. On exam, the patient appears slightly sluggish and jaundiced with icteric sclera. His temperature is 99.0°F (37.2°C), blood pressure is 88/56 mmHg, pulse is 110/min, and respirations are 22/min. His labs demonstrate an unconjugated hyperbilirubinemia of 16 mg/dL. It is determined that the best course of treatment for this patient is phenobarbital to increase liver enzyme synthesis. Which of the following best describes the molecular defect in this patient?

In a lab experiment, a researcher treats early cells of the erythrocyte lineage with a novel compound called Pb82. Pb82 blocks the first step of heme synthesis. However, the experiment is controlled such that the cells otherwise continue to develop into erythrocytes. At the end of the experiment, the cells have developed into normal erythrocytes except that they are devoid of heme. A second compound, anti-Pb82 is administered which removes the effect of Pb82. Which of the following is likely to be true of the mature red blood cells in this study?

An investigator is studying nutritional deficiencies in humans. A group of healthy volunteers are started on a diet deficient in pantothenic acid. After 4 weeks, several of the volunteers develop irritability, abdominal cramps, and burning paresthesias of their feet. These symptoms are fully reversed after reintroduction of pantothenic acid to their diet. The function of which of the following enzymes was most likely impaired in the volunteers during the study?

A 54-year-old man comes to the physician because of generalized fatigue and numbness of his legs and toes for 5 months. He has hypertension and hypercholesterolemia. He underwent a partial gastrectomy for peptic ulcer disease 15 years ago. Current medications include amlodipine and atorvastatin. He is a painter. His temperature is 37°C (98.6°F), pulse is 101/min, respirations are 17/min, and blood pressure is 122/82 mm Hg. Examination shows conjunctival pallor and glossitis. Sensation to vibration and position is absent over the lower extremities. He has a broad-based gait. The patient sways when he stands with his feet together and closes his eyes. His hemoglobin concentration is 10.1 g/dL, leukocyte count is 4300/mm3, and platelet count is 110,000/mm3. Which of the following laboratory findings is most likely to be seen in this patient?