Which organelle is not primarily involved in protein synthesis?

• A. Ribosomes
• B. Endoplasmic Reticulum
• C. Golgi apparatus
• D. Mitochondria

Answer: (D)

Proteins are made by ribosomes, which can float freely in the cytosol or be attached to the rough endoplasmic reticulum. The rough ER provides a site for synthesizing proteins that are destined to be secreted or embedded in membranes, and the Golgi apparatus then processes, tags, and ships these proteins to their final destinations. The mitochondrion, in contrast, is the cell’s powerhouse, generating most of the cell’s ATP. While mitochondria do contain their own ribosomes and can translate a small number of proteins essential for their energy functions, the organelle is not primarily involved in general protein synthesis. So, the mitochondrion is the organelle not mainly dedicated to making proteins.