Peroxisomes: what are they, characteristics and functions?

Let's see what peroxisomes are, important cytoplasmic organelles in cellular functioning.

The cell is the basic unit of existence. All living beings on Earth have at least one cell, i.e. a physiological unit capable of nourishing itself, growing, multiplying, differentiating, signaling chemical stimuli and evolving over time.

The only entities that generate conflict as far as the definition of "life" is concerned are viruses, viroids and prions, since they consist of genetic information molecules (or simple misfolded proteins) with pathogenic capacity and little else.

As far as the human being is concerned, it is estimated that our body contains an average of 30 trillion cells, divided into different lineages with specific functionality, according to their physiology, origin, origin, origin, origin, origin, origin, origin, origin, origin, origin, origin, origin and function.according to their physiology, origin and location. Red Blood cells are by far the most abundant cellular bodies in our body, occurring in orders of about 5,000,000 per cubic millimeter of blood. Undoubtedly, these oxygen transporters are one of the most basic units in the balance of our organism.

With all this data, the following statement is more than clear: we are each and every one of our cells. From the one that flakes off in the epidermis (some 30,000 every day) to some neuronal bodies that accompany us throughout our lives, each cellular unit is essential and defines us as a species and as individuals. Based on this premise, we tell you everything about peroxisomes, some very interesting cellular organelles..

What are peroxisomes?

Peroxisomes are cytoplasmic organelles found in most eukaryotic cells, i.e. those cells that have differentiated the nucleus from the rest of the cytoplasm by means of a membrane.i.e., those that have differentiated the nucleus from the rest of the cytoplasm by means of a membrane and make up multicellular living beings.

On the other hand, an organelle is defined as an elementary constituent part of the cell, which has a structural unit and fulfills a specific function. Within this category we find mitochondria, chloroplasts, vacuoles and peroxisomes, among other specific bodies.

Returning to the concept that concerns us here, it should be noted that peroxisomes are rounded organelles, delimited by a membrane and with a diameter of 0.1 to 1 micrometer.. Inside, they contain key enzymes for carrying out various metabolic reactions, including many aspects of cellular metabolism, the process by which each of these functional bodies obtains the energy necessary to carry out their activities.

It is estimated that, within each peroxisome, there are an average of 50 different enzymes capable of catalyzing various reactions, which vary according to cell type.These vary according to the type of cell containing the organelle and its physiological state. For example, these organelles contain 10% of the total activity of two enzymes involved in the pentose phosphate pathway, closely related to glycolysis (oxidation of glucose for energy).

Differences with other organelles

Peroxisomes are very different from typical organelles (mitochondria and chloroplasts) in terms of complexity and function.. They have no genetic material of their own (circular DNA), are only membrane-wrapped and do not contain mitorribosomes or chlorribosomes in their matrix.

The endosymbiotic theory postulates that mitochondria and chloroplasts were ancestral prokaryotic bacteria and archaea that were ingested, so it is difficult to match their physiological complexity within the cell.

Morphologically they are similar to lysosomes, but have in common with evolutionarily more complex organelles the fact that their component proteins are derived from cytoplasmic free ribosomes. Without the protein-building activity of ribosomes, peroxisomes, mitochondria and chloroplasts could never come into being. However, since peroxisomes have no genome of their own, all proteins must come from these cytosolic ribosomes.. In the case of mitochondria and chloroplasts, a small percentage of protein molecules are synthesized within themselves.

The functions of peroxisomes

As we have said, each peroxisome contains inside it at least 50 different enzymes depending on the cell type in which they are located. These organelles were first defined as bodies carrying out oxidative reactions, leading to the production of hydrogen peroxide, thanks to the discovery of peroxidase enzymes inside them.

As hydrogen peroxide is a harmful compound for the cell, peroxisomes also contain catalase enzymes, which decompose it into water or exploit it to oxidize other compounds. Several oxidative reactions take place in this organelle, including those of uric acid, amino acids and fatty acids.. Curiously, the enzyme urate oxidase (responsible for oxidizing uric acid to 5-hydroxyisourate) is found in many uni- and multicellular beings, but not in humans. We have the gene that encodes it, but it is not functional due to a mutation.

One of the most important fronts in which peroxisomes stand out is the oxidation of fatty acids, since these are a key source of energy for the functioning of living beings at the cellular level. for the functioning of living beings at the micro and macroscopic level. In animal cells, the oxidation of these lipid biomolecules takes place in peroxisomes and ribosomes alike, but in other species of living beings (such as yeast), peroxisomes are the only ones capable of doing so.

In addition to providing the cell with an accessory (or unique, as in the case of yeast) compartment for oxidative reactions, it should also be noted that peroxisomes are involved in lipid biosynthesis. In animals, both cholesterol and dolichol (membrane bilayer lipid) are synthesized in peroxisomes and endoplasmic reticulum (ER) alike. On the other hand, in liver cells, these multifaceted organelles are also responsible for the manufacture of bile acids, which, as we recall, come from thewhich, as we recall, come from cholesterol.

As if this were not enough, peroxisomes also contain enzymes necessary for the synthesis of plasmalogens, phospholipids that are especially important in the anatomy of cardiac and brain tissue. As you can see, peroxisomes are key centers for oxygen utilization (oxidation), but they also play many other essential roles at both the tissue and cellular levels.

Particularly plastic organelles

Finally, it is worth noting that peroxisomes show an unusual plasticity show a plasticity that is unusual in the world of organelles.. These small circular bodies can multiply in number and size in response to certain physiological stimuli, and then return to the initial situation once the exogenous trigger has disappeared. In addition, they are also capable of varying their enzymatic repertoire according to the physiological situation of the organism.

This is due to a very effective multiplication capability: strangulation. To initiate this process, the peroxisome membrane comes into contact with that of the endoplasmic reticulum (ER), an event that allows the transfer of membrane lipids from the ER to the organelle we are concerned with here, increasing its useful surface area. Once it has received this "donation", the peroxisome is capable of dividing into 2 new ones, which will mature in terms of protein content (both inside and on the membrane) as the free ribosomes make the proteins they need to function.

In addition to this, it is also worth noting that the living organism cell is capable of generating peroxisomes from scratch, when all the pre-existing ones have disappeared from the cytosol. This process is very complex at the biochemical level, but it is enough for us to know that it occurs thanks to the synthesis of vesicles in the endoplasmic reticulum and mitochondria of the cell.

Summary

When we think of cell organelles, old acquaintances automatically come to mind, such as mitochondria or chloroplasts, perhaps ribosomes and vacuoles, if we know a little more about them. Many truly interesting organic bodies present in our cytosol are lost along the way, and peroxisomes are a clear example of this.

These multifaceted organelles contain more than 50 different types of enzymes, many of them specialized in the oxidation of substances, essential for the cell to obtain metabolic energy to carry out its functions. In addition, their ease of growth in number and size allows the cell to adapt to environmental demands quickly and effectively. Undoubtedly, these small organelles are essential for the life of those who carry them.

Bibliographic references:

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