Endoplasmic reticulum

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The endoplasmic reticulum is formed by channels delimited by membranes. These channels communicate with the nuclear envelope (nuclear membrane). The endoplasmic reticulum can be considered a distribution network, taking material from which the cell needs, from any point to their point of use. The endoplasmic reticulum transport function is thus serving as a channel of communication between the cell nucleus and cytoplasm .

Rough endoplasmic reticulum

The rough endoplasmic reticulum (RER) is formed by systems of tubules and flattened ribosomes attached to the membrane which gives a granular appearance. Function: Participates in the synthesis of proteins , which are sent to the outside of cells . The endoplasmic reticulum is also called ergastoplasm, originated from the Greek word ergozomai, which means elaborate, synthesize. This type of reticulum is highly developed in cells with secretory function. This is particularly the case for the cells of the pancreas , which secrete enzymes digestive, and also the case of goblet cell wall of the intestine , which secrete mucus . Electron microscopy revealed the presence within the cytoplasm of a reticulum membrane lipoprotein that has been called the endoplasmic reticulum (ER). Depending on the position of the membranes, we can distinguish the existence of tubules and saccular or flattened vesicles. The rough endoplasmic reticulum has the following functions: it increases the internal surface of the cell, which broadens the activity of enzymes, facilitating the occurrence of chemical reactions necessary for cell metabolism, protein synthesis (its main function) and storage. Thanks to the ribosomes attached to their membranes, rough endoplasmic reticulum acts in the production of certain cellular proteins such as collagen which is a protein produced by the RER of the fibroblasts. The rough endoplasmic reticulum, may also be called the rough endoplasmic reticulum.

Smooth endoplasmic reticulum

The agranular or smooth endoplasmic reticulum (REL) is formed by systems of cylindrical tubules without ribosomes attached to membrane. Function: mainly participates in the synthesis of steroids , phospholipids and other lipids . It also acts on the degradation ofingested ethanol in alcoholic beverages, as well as the degradation of drugs ingested by the body as antibiotics and barbiturates (anesthetic substances), so the REL has, as one of its functions, detoxification of the body. This type of reticle is especially abundant in cells of the liver , the gonads and pancreas .

The smooth endoplasmic reticulum is composed of a three-dimensional network of interconnected tubules and cisterns, which extends from the nuclear membrane (the ER cisterna is continuous with the perinuclear cistern) to the plasma membrane. It is divided into two sectors: RERugoso - with poliribossomas adhered to the cytosolic face - and relise - which does have polyribosomes attached, shows different enzyme and protein composition of its membrane and content.

The binding of polyribosomes to the cytosolic surface of the RER is made by integral proteins: Docking protein (receptor recognition particle signal) Riboforinas I and II (receptor proteins from the ribosome) Protein Poro

The presence of polyribosomes in the RER enables its function: protein synthesis. For this he developed and so intense in cells with protein synthesis for export or organelle membrane. In addition, the RER also participates in protein post-translational modifications: sulfation, glycosylation and folding.

Peroxisome is a Organito or organelle spherical, surrounded by a membrane vesicle, present in the cytoplasm , especially in animal cells. Are the organelles responsible for storage of enzymes directly related to the metabolism of peroxide of hydrogen , highly toxic substance to the cell. In cellular metabolism is hydrogen peroxide (H2O2) (the hydrogen peroxide , toxic chemical to the body by being a source of free radicals ). There is present a typical enzyme called catalase that breaks down hydrogen peroxide into water ( H2O ) and oxygen ( O2 ) molecules.

This organelle is of great importance since it has the ability to degrade toxic compounds into the cell transforming them into less toxic compounds. The products will be degraded are marked bypex5 that leads to the peroxisome where it acts on the catalases and oxidases are enzymes that catalyze its conversion to hydrogen peroxide .

Peroxisomes are organelles of a single cell membrane (mitochondria are the only double membrane) from 0.2 to 1 microns in diameter that is present in eukaryotic cells. In mammals, these organelles were considered unimportant until Goldfischer discovered the absence of these organelles in the liver and the proximal tubule in renal syndrome patients with Zellweger (cerebro-hepatorenal). It is a congenital disease, clinically described for the first time in 1964, involving the brain, liver, adrenal gland, bone and kidney. The absence of peroxisomes causes serious diseases, as well as defects in their enzymes , leading to metabolic failure (1).

The investigations in this field has been intense in the last two decades. Today, many enzymes are known to be located in peroxisomes, many of which are related to lipid metabolism . In particular, beta-oxidation of fatty acids of very long chain ( VLCFA , ie fatty acids with 24 or more carbon atoms) are initially metabolized within peroxisomes. When the carbon chain is reduced to a length of 22 carbon atoms, Beta-oxidation can proceed within the mitochondria (1).

Characterization

Peroxisomes were described for the first time by Rodhin (1954), in cells of mouse , then being called "microbodies". However its biochemical characterization was due to De Duve et al. In 1966, De Duve proposed the appointment of peroxisome instead of the "microbodies", then widespread, noting the simultaneous existence in these organelles, two classes of enzymes: oxidase -producinghydrogen peroxide (hydrogen peroxide) and catalase . Subsequently, peroxisomes were identified in many animal and plant cells.

Peroxisomes (Px) are formed from the reticulum. Closed oxidase and catalase, which often are condensed into bodies of crystalline structure (cr).

Peroxisomes are small membrane vesicles, spherical or ovoid, usually less than the mitochondria . Its matrix is ​​presented, usually with a finely granular texture and often contains a dense body which recognizes a crystalline structure, known as crystalloids or "core". The crystalloid result from the progressive crystallization of catalase or oxidase existing in the matrix.

Functions

In general, peroxisomes involved in substrate oxidation in the presence of molecular oxygen and then perform the decomposition of hydrogen peroxide from those oxidations. This competency biochemistry of peroxisomes is used by different cell types with diverse objectives. In plant cells, peroxisomes involved in photorespiration and, among other functions, promote the conversion of fat into carbohydrate , when the germination of seeds of oil (in this case are called Glyoxysome ). This includes the beta-oxidation of fatty acids , which also takes place in the liver , the kidneys and other organs of mammals. In animals, peroxisome still involved in numerous other segments catabolic ( catabolism of purines , oxidizing ethanol , etc..) and anabolic (synthesis of bile acids, the synthesis of cholesterol ).

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