Practice Test 8 - USMLE Step 1

20 questions. Answer them in any order, then submit to see your score and every explanation.

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1. This patient's condition is associated with an increased risk of which of the following cardiovascular abnormalities?
2. Right ptosis, dilated pupil, left intention tremor, no weakness. Lesion?
3. Cyanide exerts its toxic effect by binding to the ferric (Fe³⁺) iron of cytochrome a₃. This action directly inhibits which component of cellular respiration?
4. The oncogenic potential of this virus is primarily mediated by viral proteins that functionally inactivate which of the following host proteins?
5. A deficiency of which of the following enzymes best explains this patient's clinical and laboratory findings?
6. Endothelial dysfunction in the pulmonary arterioles of this patient leads to an imbalance characterized by decreased production of vasodilators and increased production of vasoconstrictors. Which of the following pairs reflects this imbalance?
7. The patient's decompensation after glucose administration is due to an increased requirement for a vitamin cofactor essential for the function of which of the following enzymes?
8. Lithium is thought to produce both its therapeutic and certain adverse effects, such as nephrogenic diabetes insipidus, by interfering with which of the following signaling pathways?
9. A 72-year-old man with heart failure and CKD stage 3 is taking digoxin for rate control. He presents with nausea, yellow-green vision changes, and frequent premature ventricular contractions. Labs: creatinine 1.9 mg/dL, estimated GFR 35 mL/min/1.73 m$^2$, potassium 3.1 mmol/L, magnesium 1.5 mg/dL, digoxin level 2.6 ng/mL (therapeutic 0.5–0.9). Digoxin has Vd $\approx 7\ \text{L/kg}$ and is primarily renally cleared; normal half-life is ~36 hours, longer in renal impairment. What adjustment to the dosing regimen is most appropriate given the pharmacokinetic data?
10. The lack of effect from flumazenil is best explained by its mechanism of action as a specific antagonist at which receptor site?
11. A 28-year-old woman with migraines takes sumatriptan during aura. The pain usually resolves within 30 min. Which downstream signaling event occurs after sumatriptan binds its vascular serotonin receptor?
12. What is the role of vitamin K in reversing the effects of warfarin?
13. Which of the following molecular defects would be most prominent in these cells during DNA replication?
14. Which of the following techniques, based on the amplification of nucleic acids, is the gold standard for diagnosing HSV infection in the CSF?
15. A randomized controlled trial tests a new long-acting insulin in 480 adults with type 1 diabetes (ages 18–45; diabetes duration 12 years). Hypothesis: the new insulin reduces severe hypoglycemia over 12 months compared with standard basal insulin. Randomization is centralized; open-label administration occurs because devices look different, but outcome adjudicators are blinded. Severe hypoglycemia is defined as requiring assistance. Results: severe hypoglycemia occurs in 28/240 (11.7%) new insulin vs 44/240 (18.3%) standard. Investigators note clinicians might counsel patients differently if they know assignment. Which bias is most likely to affect the results of this study?
16. Warfarin exerts its therapeutic effect by inhibiting an enzyme that is required for the regeneration of the active form of this vitamin. The vitamin itself is a cofactor for which of the following enzymes?
17. The conversion of lactate to glucose in the liver is best described by which of the following metabolic pathways?
18. A 55-year-old man with Parkinson disease experiences wearing-off phenomena where his motor symptoms return before his next scheduled levodopa dose. His neurologist explains that this relates to the progressive loss of dopamine neurons and their capacity for neurotransmitter storage and release. Which of the following neurophysiological changes best explains the development of this wearing-off effect?
19. A 31-year-old man has chronic diarrhea and dermatitis herpetiformis; anti-TTG IgA positive. Which physiological process is likely disrupted?
20. What is the primary mechanism of action of pralidoxime, the second medication administered in this case of organophosphate poisoning?

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