What is the primary function of rough endoplasmic reticulum?

The primary function of rough endoplasmic reticulum (RER) is closely related to its role in protein synthesis and processing. The rough endoplasmic reticulum is studded with ribosomes on its cytoplasmic surface, giving it a "rough" appearance. These ribosomes are the sites of protein synthesis, where amino acids are assembled into polypeptide chains based on the genetic instructions provided by mRNA.

As proteins are synthesized by the ribosomes on the RER, they enter the lumen of the rough endoplasmic reticulum where they undergo folding and post-translational modifications, such as glycosylation. Once properly folded and modified, the proteins are packaged into vesicles that transport them to their next destination, which may include secretion outside the cell or delivery to different organelles.

While options like storing food and waste materials or conducting nerve impulses pertain to other cellular functions, the rough endoplasmic reticulum is particularly specialized for the synthesis and transport of proteins. The ability to transport materials, especially proteins produced in its ribosomes, underscores its central role in cellular function. Therefore, the correct answer highlights the RER's essential function in the transport of synthesized proteins throughout the cell.