Free USMLE® Step 1 Biochemistry Questions

Are you preparing for USMLE® Step 1? Biochemistry makes up 14–24% of the Step 1 exam. Try 10 free biochemistry practice questions below or access more in Lecturio’s all-in-one USMLE Step 1 Qbank.
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Preview 10 Free USMLE® Step 1 Biochemistry Practice Questions

The most effective way to succeed in your biochemistry course is to combine different learning modalities:
First, deep-dive into the topics with video lessons and Lecturio’s Concept Pages. Next, apply what you’ve learned in practical situations by answering clinical case questions in the Qbank to best prepare for your exam.

A 44-year-old man presents to an oncologist after being diagnosed last week with small cell lung carcinoma confirmed by biopsy. He had worked as a plant technician in the metal processing unit of a factory for the last 14 years. His family history is unremarkable. His oncologist concludes that this cancer is most likely mediated by mutations triggered by chronic chemical exposure at his work. Which of the following enzymes is primarily inhibited at the biochemical level by the chemical agent responsible for this patient’s condition?

A. Pyruvate dehydrogenase

B. Phosphofructokinase

C. Dihydrofolate reductase

D. Glucose-6-phosphate dehydrogenase

E. Aconitaseandibular branch

A 5-month-old boy presents to the pediatrician for increasing irritability over the past three weeks. The boy’s mother also reports that he is no longer sleeping through the night and has episodes of respiratory distress. She has noticed that his skin is cool and clammy in the morning. Physical examination reveals hepatomegaly. Laboratory findings show hypoglycemia with elevated lactate, uric acid, and triglyceride levels. Which of the following enzymes is most likely deficient in this patient?

A. Debranching enzyme

B. Hepatic glycogen phosphorylase

C. Lysosomal α-1,4-glucosidase

D. Muscle glycogen phosphorylase

E. Glucose-6-phosphatase

A 6-year-old boy presents with bleeding gums. His past medical history reveals a recent supracondylar fracture of the right humerus due to a fall while playing. On physical examination, petechiae are seen all over the patient’s body. The patient’s tongue is shown in the image. Which of the following is the most likely cause of this patient’s condition?

A. Child abuse

B. Osteogenesis imperfecta

C. Menkes disease

D. Vitamin C deficiency

E. Ehlers-Danlos syndrome

Scorbutic tongue
Image by CDC Public Health Image Library. License: CC0 1.0

A 7-year-old boy and the rest of his family visit a physician for a physical after migrating to the United States. His mother reports that her son is always tired and had no energy to play like the other kids in their remote village in Nigeria. He was born at 39 weeks’ via spontaneous vaginal delivery and is meeting all developmental milestones. He is behind on most of his vaccines, and they have developed a plan to get him caught up. On examination, the boy presents with jaundice, mild hepatomegaly, and tachycardia. A CBC with manual differential reveals atypical appearing red blood cells, consistent with sickle cell disease. It is expected that 2,3-bisphosphoglycerate at the biochemical level should be high in this patient. Which of the following is true of this molecule’s role in metabolism?

A. an intermediate of glycolysis

B. an intermediate of the TCA cycle

C. an intermediate of ketogenesis

D. an intermediate of the urea cycle

E. it performs its function in the mitochondrial intermembrane space

A 12-month-old boy presents to his pediatrician for a follow-up appointment. He was recently diagnosed with failure to thrive and developmental delay; all 3 major growth measurements are below the 1st percentile for his age: his weight is 7 kg (15.4 lb), height is 61 cm (24 in), and head circumference is 42 cm (16.5 in). The patient’s father had a younger sister who had mental and physical growth delays and died at a very young age. The patient was able to raise his head at the age of 7 months and began to sit alone only recently. He babbles, coos, and smiles at other people. Vital signs are blood pressure 75/40 mm Hg, heart rate 147/min, respiratory rate 28/min, and temperature 36.4°C (97.5°F). He has coarse facial features with small deep orbits, proptotic eyes, large lips, and gingival hyperplasia. His skin is pale with decreased elasticity. Lung and heart sounds are normal. There is diminished anterior abdominal wall muscle tone and hepatomegaly. Muscle tone is increased in all muscle groups of muscles in the extremities. The physician tests for suspected hereditary diseases. A blood test shows increased serum lysosomal enzyme concentration and decreased N-acetylglucosamine-1-phosphotransferase (GlcNAc phosphotransferase) activity within the leukocytes. What causes clinical symptoms in a patient with this lysosomal enzyme deficiency?

A. Dysfunctional metabolism of sphingomyelin and accumulation within the lysosomes

B. Impaired hydrolysis of GM2-ganglioside and accumulation in the cytoplasm

C. Lack of mannose phosphorylation on N-linked glycoproteins

D. Glycogen accumulation within the hepatocytes

E. Defective glycolysis resulting in a total energy deficiency

A 72-year-old man presents to the hospital with retrosternal chest pain and shortness of breath. The pain started 5 hours before arrival and has not changed after taking sublingual nitroglycerin. The patient has a history of long-standing persistent atrial fibrillation but had not been taking anticoagulants at the time of presentation. He had also been diagnosed with iron-deficiency anemia 3 months before admission and is taking 120 mg of elemental iron daily. ECG shows inferior ST-elevation myocardial infarction. The patient is managed with percutaneous coronary intervention (PCI) of the right coronary artery within an hour of arrival. A few hours later, he develops cardiogenic shock and ultimately dies about 8 hours after his arrival. The autopsy reveals extensive inferior-posterior myocardial infarction, and the image shows a slide of tissue from his heart. Which of the following statements regarding this patient’s cardiac tissue is true?

A. There is coagulative necrosis of the myocytes.

B. The changes in the myocardial tissue result from lipid peroxidation during the patient’s lifetime.

C. The changes are a result of iron overload.

D. The slide shows cardiac steatosis.

E. The microscopic image reveals myocardial hypertrophy.

Cardiac myocyte showing lipofuscin pigment
Image: by Department of Pathology, Calicut Medical College. License: CC BY-SA 4.0

A 67-year-old man is brought to the hospital by his relatives. He complains of early satiety, abdominal discomfort after food intake, and abdominal bloating. These symptoms have been present since the patient was 52, but they were milder at that time, so he has paid little attention to them since. Tingling and decreased sensation in both lower extremities began a few months ago. His relatives also note that he has become excessively somnolent and forgetful. The patient’s medical history is significant for acute hepatitis B 20 years ago. He smokes a pack of cigarettes per day and drinks alcohol occasionally. His weight is 61 kg (134.5 lb), height is 181 cm (5 ft 11 in), and BMI is 18.6 kg/m2. His vital signs are temperature 36.1°C (96.9°F),  heart rate 89/min, respiratory rate 13/min, and blood pressure 110/80 mm Hg. The patient’s skin is pale, thin, and dry. There is no significant lymphadenopathy or thyromegaly. Lung and heart examinations are within normal limits. The patient’s tongue is bright red with atrophic papillae. The abdomen is distended and tender to palpation in the epigastric area. Neurological examination shows symmetric decreased sensation and decreased muscle strength in both upper and lower extremities. On a mini-mental status examination, the patient scores 25 (slightly low). The patient’s blood test results are as follows:

Erythrocytes2.8 x 109/mm3
Hb8.6 g/dL
Mean corpuscular hemoglobin 49.9 pg/cell (3.1 fmol/cell)
Mean corpuscular volume122 fL (normal 80–100 fL)
Reticulocyte count0.3%
Total leukocyte count3,070/mm3
Platelet count195,000/mm3
Fasting plasma glucose4.6 mmol/L (82.9 mg/dL)
Aspartate aminotransferase22 U/L
Alanine aminotransferase19 U/L
Amylase32 U/L
Total bilirubin32 µmol/L (1.87 mg/dL)
Conjugated bilirubin8 µmol/L (0.4677 mg/L)

Which of the following options best explains the patient’s neurological and psychiatric symptoms?

A. Chronic bilirubin toxicity

B. Chronic hyperglycemia

C. Chronic acetaldehyde influence

D. Impaired methylation of myelin phospholipids

E. Influence of pseudo-neurotransmitters

A 50-year-old woman is brought by her husband to the emergency department with complaints of bone pain, muscle cramping, and difficulty in walking. The patient has a long history of intravenous heroin abuse, progressive difficulty in walking for the past two years, and has been confined to the bed for the past 2 months. Her husband has been bringing her both food and heroin. She denies diarrhea or floating stools but admits that she eats very little because of her poor appetite. She denies any falls or trauma and states that she has not had a menstrual period for more than 15 years. Physical examination reveals a severely underweight woman in no acute distress. Radiographs of the right leg are shown below. Which of the following laboratory blood test results would be most consistent with both clinical history and the radiological findings?

A. Calcium 11.3 mg/dL (reference range: 8.4–10.2 mg/dL)

B. Parathyroid hormone 46 pg/mL (reference range: 14–65 pg/mL)

C. Phosphorus 5.2 mg/dL (reference range 3.0–4.5 mg/dL)

D. Albumin 4.2 g/dL (reference range 3.5–5.5 g/dL)

E. Alkaline phosphatase 320 U/L (reference range 20–70 U/L)

Radiographs of the right distal femur
Image by Leslie Gamache and Mark R. Burge. License: CC BY 3.0
Radiographs of the right distal femur1
Image by Leslie Gamache and Mark R. Burge. License: CC BY 3.0

A researcher is investigating the relationship between inflammatory mediators and omega-3 fatty acids, namely docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), in post-MI patients. IL-1ß is an important pro-inflammatory cytokine involved in fibrosis and arrhythmias in the post-MI period. Research indicates that it causes loss of function in the gap junction protein connexin 43 (Cx43), resulting in an arrhythmogenic state. They perform an experiment investigating the cardioprotective effect of DHA on patients after a recent MI. Their results are shown in a Western blot analysis. Which of the following is the most accurate conclusion from these results?

A. Fatty acids with 3 cis-double bonds are cardioprotective against the effects of IL-1β in post-MI cells.

B. Fatty acids with double bonds in the 3rd position adjacent to the carboxy-terminus are cardioprotective against the effects of IL-1β in post-MI cells.

C. Fatty acids with double bonds in the 3rd position adjacent to the terminal carbon are cardioprotective against the effects of IL-1β in post-MI cells.

D. Fatty acids with 3 cis-double bonds provide minimal benefits against arrhythmias after myocardial infarctions.

E. Fatty acids with double bonds in the 3rd position adjacent to the carboxy-terminus provide minimal benefits against arrhythmias after myocardial infarctions.

F. Fatty acids with double bonds in the 3rd position adjacent to the terminal carbon provide minimal benefits against arrhythmias after myocardial infarctions.

Image by Baum et al. License: CC BY 3.0

A group of scientists is verifying previous research on DNA replication. The diagram illustrates the theoretical DNA replication process in bacteria such as Escherichia coli. What does the letter ‘a’ represent in this process?

A. RNA Primers

B. Okazaki fragments

C. Single-stranded DNA binding proteins

D. The leading strand

E. Replication fork

Image by Lecturio

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