What is the main difference between rough and smooth endoplasmic reticulum?

The main difference between rough and smooth endoplasmic reticulum lies in the presence of ribosomes on their surfaces. Rough endoplasmic reticulum, characterized by its ribosome-studded appearance, is primarily involved in the synthesis of proteins. These proteins are often destined for secretion or for use within the cell. The ribosomes attached to the rough ER translate messenger RNA into polypeptide chains, which then enter the lumen of the rough ER for further processing and folding.

On the other hand, smooth endoplasmic reticulum lacks ribosomes and is not involved in protein synthesis. Instead, it plays a crucial role in the synthesis and storage of lipids, metabolism of carbohydrates, and detoxification processes. This distinction in structure and function highlights the specialized roles that each type of endoplasmic reticulum plays within the cell. Thus, the presence of ribosomes on rough ER is what differentiates it clearly from smooth ER in terms of function and purpose.