Ultrastructure of cells · USMLE Step 1

Which of the following organelles is not bound by a membrane according to ultrastructural studies but is abundant in the cytosol and involved in protein synthesis?

  1. Mitochondria
  2. Ribosome
  3. Golgi apparatus
  4. Lysosome
Show answer and explanation

Correct answer: Ribosome

Ribosomes are non-membrane-bound macromolecular complexes visible under EM as dense particles, present free in cytosol or attached to rER; they are essential for protein synthesis.

Difficulty: Medium Question 7 of 21

Practice all 21 Ultrastructure of cells questions

Keep practicing

More Ultrastructure of cells questions