What is the primary function of the smooth endoplasmic reticulum?

The smooth endoplasmic reticulum (SER) plays a crucial role in the metabolism of lipids. It is primarily involved in the synthesis of phospholipids and cholesterol, which are essential components of cellular membranes. Additionally, the SER participates in the detoxification of drugs and harmful substances by metabolizing them into less toxic forms. The smooth ER does not have ribosomes attached to its surface, which distinguishes it from the rough endoplasmic reticulum, where protein synthesis occurs. This lack of ribosomes highlights its specialization in lipid metabolism rather than in protein synthesis or other cellular processes such as DNA replication or cell division.