What is the name given to the portion of the endoplasmic reticulum that is free of ribosomes?

The portion of the endoplasmic reticulum that is free of ribosomes is referred to as the Smooth ER. This structure is involved in several crucial cellular processes, such as lipid synthesis, metabolism of carbohydrates, detoxification of drugs and poisons, and storage of calcium ions. Unlike Rough ER, which is studded with ribosomes and primarily responsible for the synthesis of proteins destined for secretion or for use within lysosomes, Smooth ER does not have ribosomes attached to its membrane, giving it a smooth appearance.

The other options are related to different cellular structures or functions; for instance, the Rough ER is characterized by its ribosomes and involvement in protein production. Glycoproteins refer to molecules that consist of carbohydrates attached to proteins, and the Golgi apparatus functions in modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles, but none of these are synonymous with the portion of the endoplasmic reticulum that lacks ribosomes.