Ultrastructure of cells · USMLE Step 1

Which structure, visible under electron microscopy, regulates transport between the cell nucleus and cytoplasm?

  1. Cytosolic free ribosomes
  2. Pores within the nuclear envelope
  3. Smooth endoplasmic reticulum
  4. The peroxisomal membrane
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Correct answer: Pores within the nuclear envelope

The nuclear envelope is perforated by nuclear pore complexes that control the bidirectional transport of RNA, proteins, and other molecules between nucleus and cytoplasm; these pores are visible under high-resolution EM.

Difficulty: Medium Question 10 of 21

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