Endoplasmakalvon

Endoplasmakalvon, in Finnish biology usage, refers to the membrane of the endoplasmic reticulum (ER), a extensive network of membranous tubules and sacs that is continuous with the outer membrane of the nuclear envelope in most eukaryotic cells. The ER membrane lies within the cytoplasm and forms a dynamic, interconnected system that supports numerous cellular processes.

The ER membrane is a phospholipid bilayer embedded with integral and peripheral proteins. The membrane topology creates two faces: a cytosolic face and a luminal (intracellular) face. The rough endoplasmic reticulum bears ribosomes on its cytosolic surface, enabling co-translational translocation of nascent polypeptides into the lumen or into the membrane. The smooth ER lacks ribosomes and is enriched in enzymes involved in lipid synthesis, carbohydrate metabolism, and detoxification in some cell types. The ER membrane is continuous with the nuclear envelope, and its lumen serves as a compartment for protein folding, modification, and quality control.

Key functions include synthesis and processing of secretory and membrane proteins, proper folding assisted by chaperones, disulfide bond formation, and N-linked glycosylation. The ER also participates in lipid biosynthesis and distribution, and in calcium storage and homeostasis within the lumen. ER-derived vesicles ferry cargo to the Golgi apparatus for further processing.

ER stress and the unfolded protein response (UPR) can arise when folding capacity is overwhelmed, influencing cell fate and contributing to various diseases if chronic.