The rough endoplasmic reticulum synthesizes proteins while the function of the smooth endoplasmic reticula is to synthesize steroids and lipids; regulate calcium concentration, drug metabolism, as well as attachment of receptors on cell membrane proteins; and metabolize steroids (but not lipids) and carbohydrates.ough Endoplasmic Reticulum Function. The endoplasmic reticulum (ER) is an organelle in eukaryotes that forms an interconnected network of vesicles, tubules, and cisternae within cells. There are two types of endoplasmic reticulum: the rough and smooth endoplasmic reticulum.