Endoplasmatiska

Endoplasmatiska nätverket, commonly referred to as the endoplasmic reticulum (ER), is a continuous membrane-bound organelle that forms an extensive network of tubules and flattened sacs within the cytoplasm of most eukaryotic cells. It is connected to the outer membrane of the nuclear envelope and extends throughout much of the cytoplasm.

Two structural forms exist: rough endoplasmic reticulum (RER) studded with ribosomes on the cytosolic surface, and smooth endoplasmic reticulum (SER), which lacks ribosomes. The ER lumen provides space for protein folding and processing, while the outer ER membrane serves as a site for synthesis and translocation of many proteins and lipids.

Functions include synthesis of membrane and secretory proteins (RER), protein folding with chaperones, and quality control via the unfolded protein response; glycosylation and initial post-translational processing; lipid and steroid synthesis (SER); detoxification of drugs and xenobiotics; and storage of calcium ions in muscle and other cells.

ER-processed proteins are packaged into vesicles and transported to the Golgi apparatus for further processing. The ER works with other organelles in lipid metabolism, carbohydrate metabolism, and calcium signaling; perturbations can lead to ER stress and disease.

ER is ubiquitous in eukaryotes, varying in abundance with metabolic demand; it is a defining feature of the endomembrane system that evolved to organize cellular biosynthesis and trafficking.

Historically, the term endoplasmatiska nätverket appears in Swedish biology to denote this organelle, contrasting with the ectoplasm at the cell cortex.