Which organelle is primarily responsible for protein synthesis?

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

Answer: (A)

Protein synthesis is carried out by ribosomes. These tiny RNA-protein machines read the genetic code carried by mRNA and assemble amino acids into a growing polypeptide chain, which then folds into a functional protein. Ribosomes exist freely in the cytoplasm or attached to the rough endoplasmic reticulum; the latter location helps tailor proteins that will be secreted or become part of membranes. The actual work of building proteins happens at the ribosome, while the nucleus provides the mRNA blueprint through transcription, and the Golgi apparatus handles modification, sorting, and shipping of proteins after synthesis.