Peroxisomas: function and structure

Peroxisomes are essential organelles for a cellthey are characterized by their irregular form and a diameter ranging between 0.1 and 1 µm. They are found in almost all eukaryotic cells and perform crucial metabolic functions. These organelles are delimited by a membrane that houses oxidative enzymes, mainly Peroxidase and catalase. Peroxidase catalyzes the oxidation of various substrates using oxygen, generating hydrogen peroxide (H₂O₂), a potentially toxic substance. Subsequently, catalase breaks down the H₂O₂, contributing to cell detoxification.

Peroxisomes have great plasticity; These organelles can Increase in number and size in response to physiological stimuliadapting to the metabolic needs of the cell. In mammalian tissues, it is common to find hundreds of peroxisomes, which have significant heterogeneity in terms of their enzymatic content, size and shape. The Proteins associated with peroxisomesknown as peroxins, are fundamental for the incorporation of enzymes inside peroxisomes or in their membrane. These proteins, which include PEX5, PEX19, PEX3 and PEX16, facilitate the maturation and growth of peroxisomes, ensuring their functionality in metabolic and detoxification processes.

They perform metabolic reactions.

• Among the most representative enzymes that house in them are catalase and oxidase uato. These enzymes participate in oxidation processeswhere hydrogen peroxide (H₂O₂) is generated, a highly reactive and toxic molecule. Catalase plays a crucial role in inactivating the H₂O₂, transforming it into water through the reaction: h₂o₂ + r-h₂ → r + 2h₂o.
• Peroxisomes mainly participate in these two metabolic processes: the lipid metabolism and cell protection against peroxides. In mammals, these organelles are responsible for the degradation of long chain lipids and branches, as well as D-amino acids and polyamines.
• In plants, peroxisomas are essential for photorerspirationa process that oxidizes residual products of CO₂. During germination, in the seeds, they transform into glioxisomes, storing reserves and turning fatty acids into sugars through the glioxylate cycle.
• Participate in the Biosynthesis of plasmalogens and precursors of cholesterol. In some organisms, such as yeasts, they facilitate the assimilation of alcohol.
• Peroxisomes too interact with other organellessuch as mitochondria and endoplasmic reticulum, by vesicles and contacts membrane-membrane, ensuring communication and flow of essential metabolites.

First, these organelles are surrounded by a single membranewhich consists of a Lipid bilayer. This membrane delimits the internal environment of the cytosol peroxisome, which facilitates the capture and conversion of reactive molecules, such as hydrogen peroxide (H₂O₂), in less harmful compounds.

The interior of the peroxisome, called matrix, houses a variety of enzymes that catalyze crucial oxidation reactions For cell metabolism. These enzymes are synthesized in the cytoplasm and are imported to peroxisomes by specific guidance signals, such as the sign of peroxisomes 1 (PTS1) and the PTS2. The importation of proteins and lipids through the peroxisomal membrane is essential for the growth and replication of these organelles, which are divided similarly to mitochondria and chloroplasts.

It is also important to point out how the Peroxisomas biogenesisthis is done in two main ways: through the growth and division of pre -existing peroxisomes, or by generation from the endoplasmic reticulum and the mitochondria in the absence of previous peroxisomes.

• In the first process, peroxisomes They grow by addition of lipids from the endoplasmic reticulumfacilitated by physical contacts, and are divided by strangulation, a mechanism similar to that of mitochondria.
• In the second process, they are generated New Peroxisomes from vesicles from endoplasmic reticulum and mitochondria. These vesicles, known as pre-butxisomales, merge to form pre-butxisomes, which mature by incorporating cytosol proteins. The presence of peroxins, specific proteins for the formation of peroxisomes, is crucial in this process, since they seek to insert themselves into membranes similar to those of peroxisomes.

On the other hand, peroxisomas have Membrane proteins that play a crucial role in their structural integrity, facilitating the importation of other proteins and regulating the entry and exit of molecules. Some of these proteins are synthesized in free ribosomes, while others can be produced in the endoplasmic reticulum before being transported to peroxisome. This structural and functional complexity that peroxisomes possess, means that research on the import and assembly mechanisms of peroxisomes continues to be an active study area. Especially in relation to human diseases such as Zellweger syndrome, which results from mutations in the components of these roads.

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