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MCAT Biology Question — Protein Synthesis

Synthesis of intracellular proteins is initiated at which of the following sites?


  1. Free-standing ribosomes
  2. Rough endoplasmic reticulum
  3. Golgi apparatus


  1. I only
  2. II only
  3. I and II
  4. I, II, and III
Click for Explanation
  1. True. Translation of intracellular proteins is always initiated on free-free standing ribosomes in the cytosol.
  2. False. Proteins that are destined for secretion are translated on ribosomes bound to the rough endoplasmic reticulum, but proteins with an intracellular destination are synthesized on free ribosomes.
  3. False. The Golgi apparatus is responsible for packaging proteins that are to be secreted by the cell.

Answer: A. See explanations above.

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