The primary role of the endoplasmic reticulum (ER) in protein synthesis is to serve as the site for the synthesis and folding of proteins. The rough ER, studded with ribosomes, facilitates the production of proteins destined for secretion or membrane incorporation. Meanwhile, the smooth ER is involved in lipid synthesis and detoxification processes. After synthesis, the ER also plays a role in protein modification and quality control before they are transported to their final destinations. Thus, the ER is essential for maintaining cellular homeostasis and functionality.