MCAT Biology Question -- Protein Synthesis | Next Step Test Prep MCAT Biology Question -- Protein Synthesis | Next Step Test Prep

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Initiation of protein synthesis begins on 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

 

Explanation

 

  1. True. Translation is always initiated on free-free standing ribosomes in the cytosol.
  2. False. Proteins that are destined for secretion are initially translated on ribosomes in the cytoplasm. A signal sequence is first translated at the N-terminus of the peptide, which becomes the site of attachment for signal-recognition particles (SRP). The nascent protein is then directed to the rough endoplasmic reticulum by the SRP for further translation at the ER and packaging in the Golgi.
  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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