Which of the following is NOT a function of the smooth endoplasmic reticulum?

• A. Steroid production in the adrenal cortex
• B. Protein production
• C. Detoxification of lipid-soluble drugs in the liver
• D. Controls the release of Ca2+ in muscle contraction

Answer: (B)

Smooth endoplasmic reticulum lacks ribosomes, so it doesn’t synthesize proteins. Its functions center on lipid production, detoxification, and calcium handling. In steroid-producing tissues like the adrenal cortex, the smooth ER makes steroids. In the liver, it detoxifies lipid-soluble drugs through enzymes in the smooth ER, such as cytochrome P450. In muscle, the sarcoplasmic reticulum (a form of smooth ER) stores and releases Ca2+ to trigger contraction. Protein production, however, occurs primarily on the rough endoplasmic reticulum where ribosomes are attached.