Rough endoplasmic reticulum: definition, characteristics and functions

The endoplasmic reticulum is a cellular organ formed by interconnected membranes. These membranes extend with those in the center of the cell, the cell nucleus.

There are two types of endoplasmic reticulum: one, said to be rough, the membranes form flattened cisterns with associated ribosomes, and the other called smooth, which is organized with membranes forming tubules without ribosomes.

In this article let’s talk about rough endoplasmic reticulum, What are its parts and functions.

    What is Rough Endoplasmic Reticulum

    This organelle, in addition to the rough endoplasmic reticulum, gets other names: cement gravel endoplasmic reticulum, ergastoplasm or rough endoplasmic reticulum. This organelle can only be found in eukaryotic cells.

    structurally, it is characterized by a series of channels, flattened bags and cisterns, Which are distributed throughout the middle of the cell, the cytoplasm.

    Chains made up of various peptides are introduced into these flattened bags, with which complex proteins will form. These same proteins move to other parts of the cell, such as the Golgi apparatus and the smooth endoplasmic reticulum.

    Many ribosomes are found around the sacs that make up this organelle associated with them. These structures are vesicles that can contain proteins and other substances. These ribosomes are what make it look rough when seen under a microscope.

    The main function of this structure is to synthesize proteins, which are intended for different parts of the cell to develop multiple functions, as well as to control their structural and functional quality.

    functions

    These are the main functions of the rough endoplasmic reticulum.

    1. Protein synthesis

    The rough endoplasmic reticulum has a vital function for the survival of the organism: the synthesis of proteins.

    These proteins can perform multiple functions, whether structural, being part of other organelles, acting as hormones, enzymes or transporters. Therefore, the destination of these proteins can be inside the cell where they were synthesized, Form the cell layer or go outside this cell.

    Most of the proteins that are part of cell organelles originate from the ribosomes of the endoplasmic reticulum. This synthesis reaches its final stage inside the rough endoplasmic reticulum.

    The process begins when the messenger ribonucleic acid (mRNA) binds to a small ribosomal unit and then to a large one. This is how the process called translation begins.

    The first to be translated is the nucleotide sequence, Which 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, mRNA, signal peptide and SRP moves through the cytosol to reach 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 translator, the rest of the peptide chain is translated and introduced into the network.

    An enzyme, called peptidase, breaks down the signal peptide from the rest of the amino acid chain, leaving this chain free inside the organelle.

    Once the synthesis is complete, the chain of amino acids acquires a three-dimensional structure, Possess complete protein and folds.

      2. Quality control

      The rough endoplasmic reticulum performs a fundamental function for proper organic functioning. this organelle plays an important role in detecting defective proteins or it may not be helpful to the body.

      The process begins when a protein that has been misfolded during its synthesis is detected. The enzymes in charge of this phase of the process are the group of glucosyltransferases.

      Glucosyltransferase adds glucose to the defective protein, More precisely in its oligosaccharide chain. The goal is that a chaperone, in particular calnexin, recognizes the glucose of this protein and detects it as a malformed protein, thus returning it to its place of origin so that it is well folded.

      This process occurs multiple times. If the correction is not given by this route, it is passed to the next phase.

      The protein is directed to a part called the proteasome, where it will be broken down. Several types of enzymes work there and break down the defective protein into amino acids which can be recycled to form a new, well-folded protein.

      This function of quality control and detection of the synthesized material which is not useful or which may even prove to be toxic for the cell fulfills a very important hygienic function.

      So that the cell can take care of ensure that well-formed proteins reach the point of maturation at which they are functional, While those that are not thrown away or recycled.

      Varieties of ergastoplasm

      Depending on the cell in which it is located, this organelle has differentiated structural features, and there is also the possibility of receiving another name.

      In secretory cells, the endoplasmic reticulum is rough it manifests itself in the form of numerous chains or bags arranged in parallel and little separated from each other, Enough so that the vesicles with which the substances are synthesized can form.

      In the nervous system, this organelle is called the Nissl body, Appearing as very separate cisterns with numerous free cytosol ribosomes. Some neurons, despite their organelle, barely synthesize proteins.

      Bibliographical references:

      • Anglès, AR, Zurek, N., Voeltz, GK (2009). Structure and function of the peripheral ER. Current Opinion in Cell Biology, 21 ,: 506-602.
      • Daleke DL (2007). Phospholipid flippases. The Journal of Biological Chemistry. 282, 821-825.
      • Nixon-Abell J, Obara, CJ, Weig VA, Li D., Legant WR, Xu CS, Pasolli HA, Harvey K., Hess HF, Betzig E., Blackstone C., Lippincott-Schwartz3 J. (2016). Increased spatiotemporal resolution reveals very dynamic dense tubular matrices in peripheral REs. Science. 354, 3928-2.

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