9 USMLE Step 1 Mixed Review Questions with Answers (Set 20)

These 9 quick USMLE review questions test high-yield facts that show up again and again on the exam, including Von Willebrand disease, Pancoast tumor, Vitamin B12 deficiency. Each question includes the correct answer.

Written by Dr. Ray Makar, MD, author of the Repeated USMLE Questions eBook series.

Prefer video? Watch daily USMLE case questions on MedFocus by Dr. Ray on YouTube.

How to use this page: read the question, pick your answer, then tap Show Answer and Explanation.

Questions

Question 1. A newborn has a continuous machinery-like murmur. What embryologic structure failed to close?

A- Bulbus cordis
B- Ductus arteriosus
C- Foramen primum
D- Truncus arteriosus

B-Ductus arteriosus- A persistent ductus arteriosus produces a continuous “machine-like” murmur.
The correct answer is B

 

Question 2. A researcher studies a mutation that prevents dissociation of GDP from a G protein alpha subunit. Which cellular effect is most likely?

A- Decreased second-messenger production
B- Increased adenylate cyclase activity
C- Increased ligand binding to receptor
D- Prolonged receptor activation

A- Decreased second-messenger production- G proteins must exchange GDP for GTP to become active. Failure to release GDP keeps the G protein inactive, reducing downstream second-messenger signaling.
The correct answer is A

 

Question 3. A mutation prevents phosphorylation of the regulatory light chain of myosin in smooth muscle. Which immediate cellular effect is most likely?

A- Decreased actin-myosin cross-bridge formation
B- Increased calcium release from sarcoplasmic reticulum
C- Increased troponin C binding
D- Normal contraction with increased ATP consumption

A- Decreased actin-myosin cross-bridge formation- Smooth muscle contraction requires myosin light-chain kinase phosphorylation of myosin; without it, actin-myosin interaction is impaired.
The correct answer is A

 

Question 4. A researcher is studying oxygen delivery in tissues. Which factor shifts the oxyhemoglobin dissociation curve to the right?

A- Decreased 2,3-BPG
B- Decreased temperature
C- Increased PCO₂
D- Increased pH

C- Increased PCO₂- Increased PCO₂, decreased pH, increased temperature, and increased 2,3-BPG shift the curve to the right, promoting oxygen unloading to tissues (Bohr effect).
The correct answer is C

 

Question 5. A woman has heavy menstrual bleeding and prolonged bleeding time. Platelet count is normal. Which disorder is most likely?

A- Bernard-Soulier syndrome
B- Hemophilia A
C- Von Willebrand disease
D- Vitamin K deficiency

C- Von Willebrand disease- vWF disease causes mucosal bleeding with ↑ bleeding time and normal platelet count (often ↑ PTT too).
The correct answer is C

 

Question 6. Which one of the following types of lung cancer could be accompanied by Horner’s syndrome?

A- Adenocarcinoma of the lung
B- Pancoast tumor
C- Small cell lung cancer
D- Squamous cell lung cancer

B- Pancoast tumor- Also known as non-small cell lung cancer. It occurs at the apex of the lung. It may involve the brachial plexus, stellate ganglion, and the sympathetic chain.
The correct answer is B

 

Question 7. Which one of the following vitamin deficiencies may cause megaloblastic anemia associated with glossitis and angular stomatitis?

A- Folate deficiency
B- Vitamin B12 deficiency
C- Vitamin C deficiency
D- Vitamin D deficiency

B- Vitamin B12 deficiency- It is the only type of anemia that can cause megaloblastic anemia with infections and neurological symptoms.
The correct answer is B

 

Question 8. A patient with vitamin B12 deficiency develops neurological symptoms. Which metabolic change is responsible?

A- Increased homocysteine only
B- Increased methylmalonic acid only
C- Increased homocysteine and methylmalonic acid
D- Decreased folate levels

C- Increased homocysteine and methylmalonic acid- B12 deficiency causes accumulation of both homocysteine and methylmalonic acid, leading to neurological dysfunction. B12 vs. folate: Homocysteine is elevated in both. Methylmalonic acid is the key test: it is elevated in B12 deficiency but normal in folate deficiency. Only B12 deficiency causes neurological damage (subacute combined degeneration), so giving folate alone can correct the anemia while the nerve damage continues.
The correct answer is C

 

Question 9. A patient has a mutation in mitochondrial DNA. Which pattern of inheritance is expected?

A- Autosomal dominant
B- Autosomal recessive
C- Maternal inheritance
D- X-linked inheritance

C- Maternal inheritance- Mitochondrial DNA is inherited exclusively from the mother.
The correct answer is C

 

High-yield points from this set

  • A persistent ductus arteriosus produces a continuous “machine-like” murmur.
  • messenger production- G proteins must exchange GDP for GTP to become active.
  • myosin cross-bridge formation- Smooth muscle contraction requires myosin light-chain kinase phosphorylation of myosin; without it, actin-myosin interaction is impaired.
  • Increased PCO₂, decreased pH, increased temperature, and increased 2,3-BPG shift the curve to the right, promoting oxygen unloading to tissues (Bohr effect).
  • vWF disease causes mucosal bleeding with ↑ bleeding time and normal platelet count (often ↑ PTT too).

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