Endoplasmakalvosto

Endoplasmakalvosto, commonly called the endoplasmic reticulum (ER) in many languages, is a membrane-bound organelle in eukaryotic cells. It forms an extensive, interconnected network of flattened sacs and tubules that extend throughout the cytoplasm and is continuous with the outer membrane of the nuclear envelope. The ER consists of two main regions: rough ER and smooth ER.

The rough endoplasmic reticulum is studded with ribosomes on its cytosolic surface, giving it a "rough" appearance. It is the site of synthesis and initial folding of secretory and membrane proteins, with protein quality control and post-translational modifications such as disulfide bond formation and N-linked glycosylation occurring within its lumen. Vesicles transporting newly made proteins bud from the rough ER and join the Golgi apparatus.

The smooth endoplasmic reticulum lacks ribosomes and is more involved in lipid synthesis, including phospholipids and cholesterol, as well as the production of steroid hormones in certain tissues. It also participates in carbohydrate metabolism, detoxification of drugs and toxins (especially in liver cells), and storage of calcium ions (Ca2+) in the lumen, which helps regulate various cellular processes.

Overall, the ER contributes to protein production, lipid metabolism, calcium storage, and detoxification. It communicates with the Golgi apparatus and other organelles through vesicular transport. Disturbances in ER function can lead to ER stress and the unfolded protein response, with implications for various diseases.