Ultrastructure of cells · USMLE Step 1

Which structure is most directly involved in lipid synthesis and detoxification and would appear under EM as a network of smooth tubular membranes lacking ribosomes?

  1. Rough endoplasmic reticulum
  2. Smooth endoplasmic reticulum
  3. Mitochondria
  4. Golgi apparatus
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Correct answer: Smooth endoplasmic reticulum

Smooth ER consists of membrane tubules without ribosomes; it synthesizes lipids and detoxifies certain compounds — this ultrastructural appearance helps distinguish it from rough ER.

Difficulty: Medium Question 14 of 21

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