Ultrastructure of cells · USMLE Step 1

Which organelle is characterized ultrastructurally by a network of membrane-bound tubules and cisternae, some of which are studded with ribosomes?

  1. Smooth endoplasmic reticulum (sER)
  2. Mitochondria
  3. Rough endoplasmic reticulum (rER)
  4. Peroxisome
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Correct answer: Rough endoplasmic reticulum (rER)

Rough endoplasmic reticulum (rER) is a membranous network whose cisternae have ribosomes on their cytosolic surface, giving a 'rough' appearance under EM; it is involved in synthesis of secretory and membrane proteins.

Difficulty: Medium Question 5 of 21

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