Which organelle is the site of protein synthesis?

• A. Ribosome
• B. Endoplasmic reticulum
• C. Nucleus
• D. Lysosome

Answer: (A)

Protein synthesis happens at ribosomes, the cellular machines that translate the genetic code into a polypeptide. Ribosomes read mRNA sequences and link together appropriate amino acids carried by tRNA to form the growing protein. They can float freely in the cytosol or be attached to the rough endoplasmic reticulum, where proteins destined for secretion or membranes are synthesized and then processed. The nucleus houses DNA and is where transcription occurs, not where translation happens. Lysosomes are involved in breaking down macromolecules, not making proteins. So, the site of protein synthesis is the ribosome.