Rough endoplasmic reticulum: definition, characteristics and functions.
Let's see what are the characteristics of this part of eukaryotic cells.
The endoplasmic reticulum is a cellular organ formed by interconnected membranes. These membranes are continuous with those of the cell center, the cell nucleus.
There are two types of endoplasmic reticulum: one, called rough, whose membranes form flattened cisternae with associated ribosomes, and the other, called smooth, which is organized with membranes forming tubules without ribosomes.
In this article we are going to talk about the rough endoplasmic reticulumwhich are its parts and its functions.
What is the rough endoplasmic reticulum?
This organelle, in addition to rough endoplasmic reticulum, receives other names: granular endoplasmic reticulum, ergastoplasma or rough endoplasmic reticulum.. This organelle can only be found in eukaryotic cells.
Structurally, is characterized by a series of channels, flattened sacs and cisternae, which are distributed in the middle of the cell, the cytoplasm.which are distributed in the middle of the cell, the cytoplasm.
In these flattened sacs, chains made up of various peptides are introduced, with which complex proteins are formed. These same proteins travel to other parts of the cell, such as the Golgi apparatus and the smooth endoplasmic reticulum.
Around the sacs that form this organelle are numerous ribosomes associated with them. associated with them. These structures are vesicles that can contain proteins and other substances. These ribosomes are what give it a rough appearance when viewed under the microscope.
The main function of this structure is to synthesize proteins, which are destined to different parts of the cell to develop multiple functions, in addition to controlling their structural and functional quality.
Functions
These are the main functions of the rough endoplasmic reticulum.
Protein synthesis
The rough endoplasmic reticulum has a function that is of vital importance for the survival of the organism: to synthesize proteins.
These proteins can perform multiple functions, whether structural, forming part of other organelles, acting as hormones, enzymes or transporting substances. Thus, the target site of these proteins can be the destination of these proteins can be inside the cell where they have been synthesized, forming the cell layer or going to the cellular layer.The destination of these proteins can therefore be the cell interior where they are synthesized, forming the cell layer, or going to the outside of the cell.
Most of the proteins that form part of the cell organelles have their origin in the ribosomes of the endoplasmic reticulum. This synthesis reaches its final stage inside the rough endoplasmic reticulum.
The process begins when messenger ribonucleic acid (mRNA) binds to a small ribosomal unit and then to a large ribosomal unit. This starts the process called translation.
The first thing to be translated is the nucleotide sequencewhich will synthesize a chain of about 70 amino acids. This chain is called the signal peptide. A molecule called SRP (sequence recognition particle) is responsible for recognizing this signal peptide, slowing down the translation process.
The structure formed by the two ribosomal subunits, the mRNA, the signal peptide and the SRP travels through the cytosol until it reaches the wall of the rough endoplasmic reticulum.
By means of a special protein, called a translocator, a channel is formed in the membrane through which the peptide part of the formed structure passes.. The signal peptide binds to the translocator, the rest of the peptide chain is translated and introduced into the reticulum.
An enzyme, called peptidase, cleaves the signal peptide from the rest of the amino acid chain, leaving the free chain inside the organelle.
Once the synthesis has been completed, the amino acid chain acquires a three-dimensional structure, characteristic of a complete protein.of a complete protein, and folds up.
2. Quality control
The rough endoplasmic reticulum performs a fundamental function for the proper functioning of the organism. This organelle plays an important role in detecting proteins that are defective or may not be useful for the or proteins that may not be useful for the organism.
The process begins when a protein is detected that has been misfolded at the time of synthesis. The enzymes in charge of this phase of the process are the glycosyltransferase group.
The glycosyltransferase adds a glucose to the defective protein, specifically in its oligosaccharide chain.specifically in its oligosaccharide chain. The purpose of this is that a chaperone, namely calnexin, recognizes the glucose in this protein and detects it as a misfolded protein, thus returning it to its place of origin so that it can be properly folded.
This process occurs several times. In the event that the correction does not occur by this route, it goes to the next phase.
The protein is directed to a part called the proteosome, where it will be degraded.. Here, multiple types of enzymes are at work, which disintegrate the defective protein into amino acids that can be recycled to form a new, well-folded protein.
This function of quality control and detection of what is synthesized that is not useful or may even prove to be toxic for the cell fulfills a very important hygienic function.
Thus, the cell can take care of making sure that the well ensure that well-formed proteins reach the point of maturation at which they are functional, while those that are not are discarded.while those that do not are discarded or recycled.
Varieties of ergastoplasma
Depending on the cell in which it is found, this organelle has different structural characteristics and may also be given a different name.
In the secretory cells, the rough endoplasmic reticulum manifests itself in the form of numerous chains or sacs arranged parallel to each other and not far from each otherIn secretory cells, the rough endoplasmic reticulum manifests itself in the form of numerous chains or sacs arranged in parallel and only slightly separated from each other, sufficiently so that vesicles can form with which substances are synthesized.
In the nervous system, this organelle is called Nissl bodies., apareciendo en forma de cisternas muy separadas con muchos ribosomas libres por el citosol. Algunas neuronas, pese a tener este orgánulo, apenas sintetizan proteínas.
Referencias bibliográficas:
- English, A. R., Zurek, N., Voeltz, G. K. (2009). Peripheral ER structure and function. Current opinion in cell biology, 21, :506-602.
- Daleke D. L . (2007). Phospholipid Flippases. The journal of Biological chemistry. 282, 821-825.
- Nixon-Abell J, Obara, C. J., Weig V. A., Li D., Legant W. R., Xu C. S., Pasolli H. A., Harvey K., Hess H. F. , Betzig E., Blackstone C., Lippincott-Schwartz3 J.( 2016). Increased spatiotemporal resolution reveals highly dynamic dense tubular matrices in the peripheral ER. Science. 354, 3928-2.
(Updated at Apr 14 / 2024)