Peroxisomes: What They Are, Characteristics And Functions
The cell is the basic unit of existence. All living beings on Earth have at least one cell, that is, a physiological unit capable of nourishing itself, growing, multiplying, differentiating, signaling chemical stimuli and evolving over time.
The only entities that generate conflict when it comes to the definition of “life” are viruses, viroids and prions, since they consist of molecules of genetic information (or simple poorly folded proteins) with pathogenic capacity and little else.
As far as human beings are concerned, It is estimated that our body contains an average of 30 trillion cells, divided into different lineages with specific functionality, according to its physiology, origin and location. Red blood cells are by far the most abundant cell bodies in our body, as they occur in orders of about 5,000,000 per cubic millimeter of blood. Without a doubt, these oxygen transporters are one of the most basic units in the balance of our body.
With all this data, the following statement is more than clear to us: we are each and every one of our cells. From the one that peels off in the epidermis (about 30,000 each 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, very interesting cellular organelles
Peroxisomes are cytoplasmic organelles found in most eukaryotic cells that is, those that have the nucleus differentiated from the rest of the cytoplasm by a membrane and make up multicellular living beings.
For its part, 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 is worth noting that Peroxisomes are round organelles, delimited by a membrane and with a diameter of 0.1 to 1 micrometers Inside, they contain key enzymes for carrying out various metabolic reactions, including many aspects of cellular metabolism, a process by which each of these functional bodies obtains the energy necessary to develop its activities.
It is estimated that, Within each peroxisome, there are an average of 50 different enzymes capable of catalyzing various reactions, which vary depending on the type of cell that contains 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 to obtain energy).
Differences with other organelles
Peroxisomes are very different from typical organelles (mitochondria and chloroplasts) in terms of complexity and function They do not have their own genetic material (circular DNA), they are only wrapped in a membrane and do not contain mitoribosomes or chlororibosomes 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 they have in common with evolutionarily more complex organelles the fact that the proteins that compose them come from free cytoplasmic ribosomes. Without the protein-building activity of ribosomes, peroxisomes, mitochondria, and chloroplasts could never form. Anyway, Since peroxisomes do not have their own genome, all proteins must come from these cytosolic ribosomes In the case of mitochondria and chloroplasts, a small percentage of the protein molecules are synthesized within themselves.
The functions of peroxisomes
As we have said, each peroxisome contains at least 50 different enzymes depending on the cell type in which they are found. These organelles were first defined as bodies that carried out oxidative reactions, leading to the production of hydrogen peroxide, thanks to the discovery of peroxidase enzymes inside them.
As hydrogen peroxide is a compound that is harmful to the cell, peroxisomes also contain catalase enzymes, which break it down into water or use it to oxidize other compounds. Various oxidative reactions take place in this organelle, among them 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 unicellular and multicellular beings, but not in humans. We have the gene that codes for 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 a 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 carrying it out.
In addition to providing the cell with an accessory (or unique, as in the case of yeast) compartment for oxidative reactions, it is also worth noting 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 making bile acids which we remember 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 heart and brain tissue. As you can see, peroxisomes are key centers in oxygen utilization (oxidation), but they also play many other essential roles at both the tissue and cellular levels.
Some especially plastic organelles
Finally, it should be noted that peroxisomes show an unusual plasticity in the world of organelles These small circular bodies can multiply in number and size in the face of 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 depending on the physiological situation of the organism.
This is due to a very effective multiplication capacity: strangulation. To start 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 that concerns us 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 their 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 cell of the living organism is capable of generating peroxisomes from scratch, when all the pre-existing ones have disappeared from the cytosol. This process is very complex at a biochemical level, but it is enough for us to know that it occurs thanks to the synthesis of vesicles in the endoplasmic reticulum and the mitochondria of the cell.
Summary
When we think about the organelles of the cell, old acquaintances automatically come to mind, such as mitochondria or chloroplasts, perhaps ribosomes and vacuoles, if we know more about the subject. 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 types of different enzymes, many of them specialized in the oxidation of substances, essential for the cell to obtain metabolic energy to carry out its functions. Furthermore, its ease of growing in number and size allows the cell to adapt to environmental demands quickly and effectively. Without a doubt, these small organelles are essential for the lives of those who carry them.
