Amino Acids & Proteins MCAT Practice Question
A 58-year-old woman with pernicious anemia presents with progressive paresthesias, ataxia, and cognitive decline. Laboratory studies reveal elevated serum homocysteine (42 μmol/L; normal <15) and elevated methylmalonic acid. Physical examination confirms decreased vibration sense in the lower extremities. Homocysteine is normally remethylated to methionine via methionine synthase, which requires a cofactor donated by methyltetrahydrofolate. A deficiency of which of the following would most directly explain this patient's biochemical abnormality?
Answer choices
- AVitamin B12Correct answer
- BVitamin B6
- CFolate
- DNiacin
- ERiboflavin
- FVitamin C
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.