Exploring the Intricacies of the Endoplasmic Reticulum

Endoplasmic Reticulum The endoplasmic reticulum (ER) is a very extensive membrane system found in the cytoplasm, because 50% of all membranes in a cell are ER membranes. The ER membrane has a folded structure, forming a space called the ER lumen or ER cisterna which has the shape of a labyrinth. There are two regions of the ER that are functionally different, namely the region of the ER where the cytosolic surface of the membrane is attached to ribosomes, called the granular endoplasmic reticulum (REG) or rough endoplasmic reticulum (REK). The second area that does not contain ribosomes on the cytosolic surface of the ER membrane is called the agranular endoplasmic reticulum (REA) or smooth endoplasmic reticulum (REH). These two types of endoplasmic reticulum form a membrane system that encloses a space, with the inside of the membrane called the luminal or cisternal space and the area outside the membrane called the cytosolic space. The morphological difference between the rough and smooth endoplasmic reticulum lies in the presence or absence of ribosomes bound to the membrane facing the cytosolic space. The smooth endoplasmic reticulum has a tubular structure with a smooth cytoplasmic surface. REH has various functions, especially for lipid synthesis, carbohydrate metabolism, and offering drugs and poisons. The synthesis of fatty acids and phospholipids is carried out by REH even though many cells only have a small amount of REH in them. The enzyme in liver cells REH modifies to help chemical processes to remove toxins and neutralize them into water which will be excreted from the body. If the body is attacked by toxins, it will trigger the proliferation of liver cells to produce more REH. The enzymes in REH help remove drugs and poisons, especially in liver cells. Poisoning involves adding a hydroxyl group to the drug so that the drug is easily dissolved and excreted by the body. The rough endoplasmic reticulum has a tubular structure with a rough surface because it is attached to ribosomes. REK has the main function of carrying out protein synthesis, especially proteins used for secretory products. Most eukaryotic cells have more REK than REH because they are needed for the synthesis of plasmamembrane proteins and secretory proteins. REC is usually found in certain cells that function to produce specific secretory proteins such as cells that produce antibodies, pancreatic cells that produce digestive enzymes, and pancreatic cells in the islets of Langerhans that produce the hormones insulin and glucagon. All eukaryotic cells will use the same secretion pathway to synthesize and select soluble secretory proteins in the ER, Golgi, and lysosomes. Although all cells can secrete many types of proteins (for the needs of secretory proteins in the extracellular environment), usually certain types of cells will also produce certain types of secretory proteins as well. An example is pancreatic cells which synthesize many digestive enzymes which are then distributed through vessels to the digestive area. When secretory proteins are formed, the ER membrane will keep them separate from the proteins produced by free ribosomes. Proteins synthesized in the ER will not be able to exit the ER lumen until their conformation is complete. Secretory proteins exit the ER and are wrapped in vesicle membranes to be further processed in the Golgi apparatus. These vesicles are transport organelles containing secretory proteins that need to be further refined in the Golgi apparatus.