USMLE Biochemistry Block 1


 A 28-year-old man is diagnosed with a metabolic disorder after presenting with muscle weakness and cardiomyopathy. Laboratory studies show elevated levels of long-chain fatty acids. Which enzyme is most likely deficient in this patient?

Question 1 of 15

2. A newborn child presents with poor feeding, vomiting, and lethargy. Laboratory tests reveal hypoglycemia, metabolic acidosis, and elevated levels of tyrosine and methionine in blood. Which of the following metabolic pathways is most likely affected?

Question 2 of 15

3.  A researcher is studying a particular enzyme involved in glycolysis. She notes that the enzyme is inhibited by its own end product. This is an example of which of the following regulatory mechanisms?

Question 3 of 15

4.  A 6-year-old boy presents with developmental delay, aggressive behavior, and self-inflicted injuries to his fingers and lips. His urine has a strong musty odor. Which of the following is the most likely diagnosis?

Question 4 of 15

5.  A medical student studying for his boards is trying to remember the rate-limiting enzyme in the synthesis of cholesterol. Which of the following is the enzyme he's trying to remember?

Question 5 of 15

6. A 26-year-old woman presents with a history of chronic alcoholism. She complains of double vision and has difficulty walking. Laboratory tests reveal a thiamine deficiency. Which of the following enzymatic reactions is most likely to be affected in this patient?

Question 6 of 15


A 2-year-old boy presents with delayed wound healing, dry skin, fatigue, and frequent infections. His diet largely consists of rice and noodles. Which vitamin deficiency is the child most likely suffering from?

Question 7 of 15

8. A 40-year-old man shows signs of dermatitis, diarrhea, and dementia. His medical history reveals a preference for a diet that is mainly corn-based. Which of the following vitamin deficiencies is the most likely cause?

Question 8 of 15

9. A 60-year-old woman with a history of malabsorption syndrome presents with bone pain and muscle weakness. X-rays show thinning of the bone. Which vitamin deficiency is most likely responsible for the patient's symptoms?

Question 9 of 15

10. A 30-year-old vegan woman presents with fatigue, pallor, and glossitis. A complete blood count shows macrocytic anemia. Which vitamin deficiency is the most likely cause?

Question 10 of 15

11.  A 1-week-old infant presents with failure to thrive, jaundice, and hypoglycemia. Urinalysis reveals reducing substances. Which of the following is the enzyme most likely deficient in this patient?

Question 11 of 15

12. A newborn presents with vomiting after breastfeeding, lethargy, and cataracts. Laboratory findings show elevated galactitol in the blood and urine. Which of the following conditions is the most likely diagnosis?

Question 12 of 15

13.  In classic galactosemia, accumulation of which of the following substances is primarily responsible for the development of symptoms?

Question 13 of 15

14. A newborn is diagnosed with a disorder characterized by a deficiency of galactose-1-phosphate uridyltransferase. Which of the following dietary modifications is most appropriate for this patient?

Question 14 of 15

15.  A 1-month-old infant is diagnosed with classic galactosemia. Which of the following complications is the infant most likely to develop if left untreated?

Question 15 of 15


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Facultad de Medicina: Universidad Catholica de Santiago de Guayaquil
ECFMG Certification date: October 13, 2022.
Residency: 2023 Internal Medicine Applicant
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