The smooth endoplasmic or smooth ER reticulum is an organelle that occurs both in animal cells and in plant cells. The organelle is a subunit in a cell that has a specialized function. The main function of a smooth ER is the production of cellular products such as hormones and lipids. It also distributes these products throughout the entire cell and places in the body. Smooth ER also regulates and releases calcium ions and processes toxins.
It is described as “smooth” to distinguish it from a rough ER that has ribosomes to synthesize proteins on its surface. Each organelle in the cell cytoplasm is responsible for the performance of a specific function. Rough and smooth ER produce different products for the cell.
Rough endoplasmic reticulum structure
The general structure of the endoplasmic reticulum is a network of membranes called cisternae. These pouch-like structures are held together by the cytoskeleton. A phospholipid membrane includes a storage space (or light) that is continuous in the perinuclear space but separated from the cytosol. The functions of the endoplasmic reticulum can be summarized as the synthesis and export of membrane proteins and lipids, but it differs between ER and cell type and cell function. The amount of both rough and smooth endoplasmic reticulum in the cell may slowly change from one type to another, depending on the changing metabolic activities of the cell. The transformation may involve the deposition of new proteins in the membrane as well as structural changes. Changes in protein content can occur without noticeable structural changes.
Smooth Endoplasmic Reticulum function
The surface of the rough endoplasmic reticulum (often abbreviated as RER or Rough ER) (also called the granular endoplasmic reticulum) is planted with protein-producing ribosomes, which gives it a “rough” appearance (hence its name). The translocation of the ribosome on the rough endoplasmic reticulum is the translocon. However, ribosomes are not a stable part of the organelle structure because they are constantly bound and released from the membrane.
Ribosome only binds to RER when a specific protein-nucleic acid complex is formed in the cytosol. This special complex arises when the free ribosome begins to translate the mRNA of the protein to be secreted. The first polymerized 5-30 amino acids encode a signal peptide. A molecular message recognized and bound by a signal recognition (SRP) particle. The translation stops and the ribosome complex binds to the ER translocon, where the translation continues with the nascent (new) light-forming RER and/or membrane.
The protein is processed in the ER light by an enzyme (signal peptidase) that removes the signal peptide. Ribosomes at this point can be released back into the cytosol; however, non-translational ribosomes are also known to remain associated with translocon.
The membrane of the rough endoplasmic reticulum
The membrane of the rough endoplasmic reticulum forms large double-membrane sheets that are located nearby and are continuous with the outer layer of the nuclear envelope. Double diaphragm plates are stacked and joined by several left or right-turn screws, the so-called Terasaki ramps, which form a structure resembling a multi-storey car park. Although there is no continuous membrane between the endoplasmic reticulum. The Golgi apparatus, membrane-bound transport vesicles transport proteins between these two compartments.
The bubbles are surrounded by coating proteins called COPI and COPII. COPII excels in the vesicles in the Golgi apparatus, and COPI means that they return to the rough endoplasmic reticulum. The rough endoplasmic reticulum works with the Golgi complex to direct new proteins to their correct target sites. The second mode of transport from the endoplasmic reticulum includes areas called membrane contact sites in which the membranes of the endoplasmic reticulum and other organelles are closely related, allowing the transfer of lipids and other small molecules.