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Comprehensive Basic Science Flashcards

7 cards from real NBME practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. A patient with chronic alcoholism presents with peripheral neuropathy and Wernicke's encephalopathy. Which enzyme requires the deficient cofactor?

    Answer: Pyruvate dehydrogenase

    Thiamine (B1) is required by pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and transketolase; its deficiency impairs oxidative decarboxylation.

  2. A cell exposed to hypotonic solution swells and lyses. Which membrane transport mechanism is responsible for the initial water influx?

    Answer: Facilitated diffusion via aquaporins

    Water moves down its osmotic gradient through aquaporin channels by facilitated diffusion, not requiring ATP.

  3. During DNA replication, which enzyme removes RNA primers and fills the resulting gaps with DNA?

    Answer: DNA polymerase I

    In prokaryotes, DNA polymerase I has 5'→3' exonuclease activity to remove primers and 5'→3' polymerase activity to fill gaps.

  4. A researcher blocks the proteasome in a cell. Which of the following processes is most directly impaired?

    Answer: Degradation of ubiquitin-tagged misfolded proteins

    The proteasome degrades cytosolic proteins tagged with polyubiquitin chains, including misfolded and regulatory proteins.

  5. A mutation eliminates the Shine-Dalgarno sequence in a bacterial mRNA. What is the most likely result?

    Answer: Reduced translation initiation

    The Shine-Dalgarno sequence base-pairs with 16S rRNA to position the ribosome at the start codon; its loss severely impairs translation initiation.

  6. Which glycolytic intermediate directly donates phosphate to ADP to produce ATP via substrate-level phosphorylation?

    Answer: Phosphoenolpyruvate

    Pyruvate kinase transfers the phosphate from phosphoenolpyruvate to ADP, generating pyruvate and ATP by substrate-level phosphorylation.

  7. A patient has a defect in the enzyme that hydroxylates proline residues in collagen. Which cofactor is most likely deficient?

    Answer: Ascorbic acid (Vitamin C)

    Prolyl hydroxylase requires Vitamin C as a cofactor; deficiency leads to scurvy with defective collagen cross-linking.