Which of the following functions is NOT associated with smooth endoplasmic reticulum?

The synthesis of membrane proteins is not a function associated with smooth endoplasmic reticulum (smooth ER). Smooth ER primarily specializes in the synthesis of lipids, which includes phospholipids and cholesterol, rather than proteins. It plays significant roles in transporting materials within the cell and detoxifying harmful substances. These processes are fundamental to maintaining cellular health and function.

In contrast, the rough endoplasmic reticulum (rough ER), which is studded with ribosomes, is specifically responsible for the synthesis of membrane proteins and secretory proteins. The ribosomes on the rough ER translate mRNA into polypeptides, which are then folded and processed within the lumen of the rough ER. This distinction helps to clarify the specific functions of smooth versus rough ER in cellular biology.