Which organelle is primarily responsible for protein synthesis?

The rough endoplasmic reticulum (RER) is primarily responsible for protein synthesis due to its unique structure and the ribosomes that are attached to its cytoplasmic surface. These ribosomes are the sites where amino acids are assembled into polypeptide chains, which then fold to become functional proteins. The RER plays a key role in the synthesis of proteins that are either secreted from the cell, integrated into cellular membranes, or sent to lysosomes for degradation.

Additionally, the rough endoplasmic reticulum is involved in the post-translational modification of these proteins, ensuring they acquire the necessary structure and functional capability before they are transported to their final destinations within or outside the cell. This makes it distinct from other organelles involved in the cellular processes.

While the smooth endoplasmic reticulum is associated with lipid synthesis and detoxification, and the nucleus houses the genetic material and oversees overall gene expression, neither of these organelles directly engages in the synthesis of proteins to the extent that the rough endoplasmic reticulum does. Lysosomes, on the other hand, are primarily involved in digestion and waste removal within the cell, and do not participate in protein synthesis.