The smooth endoplasmic reticulum (SER) is responsible for various cellular functions, including lipid metabolism, detoxification of drugs and toxins, and calcium storage. However, it does not transport proteins. The rough endoplasmic reticulum (RER), which is studded with ribosomes on its surface, is primarily involved in protein synthesis, folding, and transport. Transport of proteins within the cell is mediated by various transport vesicles, including the Golgi apparatus and endosomes.