What does the smooth ER do?

• A. Produces proteins
• B. Packages proteins
• C. Detoxifies chemicals and makes lipids
• D. Stores energy

Answer: (C)

The smooth endoplasmic reticulum is specialized for detoxification and lipid synthesis. It lacks ribosomes, so it isn’t the site where proteins are made; that job belongs to ribosomes on the rough ER. Instead, enzymes in the smooth ER help metabolize and neutralize drugs and other chemicals, especially in liver cells, which is why detoxification is a key function. It also synthesizes lipids, including phospholipids for membranes and cholesterol, which are essential components of cell membranes and signaling molecules. In some cells, it can store calcium ions, contributing to cellular signaling, but energy storage is mainly handled by mitochondria and other structures. Packaging and shipping proteins are tasks of the rough ER and the Golgi apparatus, not the smooth ER. So describing the smooth ER as detoxifying chemicals and making lipids best captures its role.