Which organelle makes proteins?

• A. Ribosomes
• B. Rough ER
• C. Smooth ER
• D. Golgi apparatus

Answer: (B)

Protein production starts with ribosomes translating mRNA into polypeptides. When ribosomes are attached to the rough endoplasmic reticulum, the newly formed proteins are threaded into the ER lumen where they are folded and begin initial modifications. The rough ER therefore acts as the site where many proteins destined for secretion, for membranes, or for lysosomes are synthesized and processed. While ribosomes carry out the actual synthesis, the organelle that embodies this protein-making process in this context is the rough endoplasmic reticulum because of its ribosome-studded surface and its role in producing these proteins. The smooth ER lacks ribosomes and is involved in lipid synthesis and detoxification, and the Golgi apparatus handles further modification and shipping of proteins after synthesis.