What is the primary role of the rough endoplasmic reticulum?

The rough endoplasmic reticulum (RER) is primarily responsible for the synthesis of proteins and the assembly of membrane components. Its surface is studded with ribosomes, which are the sites of protein translation. As ribosomes synthesize polypeptides, they are transported into the lumen of the RER, where they often undergo modifications, such as folding and post-translational modifications. This process is essential for producing proteins that are either secreted from the cell, incorporated into the cell membrane, or sent to lysosomes.

Additionally, the rough endoplasmic reticulum plays a vital role in membrane synthesis by providing proteins that are eventually inserted into lipid bilayers. This is crucial for maintaining the structure and function of the cell and is why the rough endoplasmic reticulum is central to both protein and membrane synthesis.