The cells seem so small and simple as they catch the eye, but there are very few cells. Cells are constantly carrying out various processes internally. When you start looking more deeply inside the cell, you’ll find a complex network of organelles that are internal cell structures that perform a cell task. The organelles in the cell will depend on the type of eukaryotic cell.


Some of the organelles you regularly hear are mitochondria, ribosomes, and a smooth and rough endoplasmic reticulum. I bet I know one organelle you do not know much about. We will discuss one organelle called peroxisomes. Peroxisomes are organelles that contain enzymes to perform their functions. Let’s move to the structure and peroxisome function.


peroxisome function

The main function of the peroxisome is the breakdown of very long-chain fatty acids by beta-oxidation. In animal cells, long fatty acids are converted into medium-chain fatty acids, which are then transferred to the mitochondria, where they eventually break down into carbon dioxide and water. In yeast cells and plants, this process takes place exclusively in peroxisomes.


Many of the processes taking place in our cells produce some not-so-safe chemicals that can be harmful to our cells and our bodies. These compounds are taken up by peroxisomes. Peroxyzom enzymes will transfer hydrogen atoms from various compounds to oxygen to produce hydrogen peroxide.



Metabolic peroxisome function

The first reactions in plasmid formation in animal cells also occur in peroxisomes. Plasmalogen is the most abundant phospholipid in myelin. The lack of plasmalogens causes profound irregularities in the myelination of nerve cells, which is one of the reasons why many peroxisomal disorders affect the nervous system.


Peroxisome functions ]

Peroxisomes also play a role in the production of bile acids important for the absorption of fat-soluble fats and vitamins, such as vitamins A and K. Skin disorders are features of genetic disorders that affect the function of the peroxisome.


Peroxisomes carry oxidative enzymes, such as D-amino acid oxidase and uric acid oxidase. However, the last enzyme is absent in humans, explaining a disease known as gout caused by the accumulation of uric acid. Some enzymes in peroxisomes, using molecular oxygen, remove hydrogen atoms from certain organic substrates (marked as R), in an oxidation reaction, producing hydrogen peroxide (H2O2, itself toxic).


Peroxisome structure

Most organelles are formed by budding the endomembrane system, but this is not the case with peroxisomes. Peroxisomes are created by taking up proteins and lipids from the cell cytoplasm. You remember the cytoplasm. It is a gel-like liquid in a cell in which organelles are suspended.


The influx of proteins and lipids increases paroxysm. When the peroxisome is large enough, it is divided by cleavage to form two peroxisomes. Peroxisomes are created in this way because they do not have their own DNA to give instructions on how to create proteins that must function. Therefore, peroxisomes must be created, containing all the necessary proteins.


Because peroxisomes are not formed from the endomembrane system, they are associated with a single membrane rather than a double membrane, like most organelles. The final result is a single membrane-associated organelle with lipids and proteins that act as enzymes.



Peroxisome assembly

Peroxisomes can be derived from the endoplasmic reticulum and replicated by fission. Peroxisome matrix proteins are transferred to the cytoplasm prior to import. Certain amino acid sequences (PTS or peroxisomal targeting signal) at the C-terminus (PTS1). N-terminus (PTS2) of the peroxisomal matrix proteins signal them to be imported into organelles. There are at least 32 known peroxisomal proteins called peroxins that participate in the peroxisome assembly process.


Proteins do not need to grow to be imported into the peroxisome. Protein receptors, PEX5, and PEX7 peroxins accompany their charges (containing the amino acid sequence PTS1 or PTS2, respectively) up to the peroxisome, where they release the charge, and then return to the cytosol – a step called recycling.


The model describing the import cycle is referred to as the extended swing mechanism. There is no evidence that ATP hydrolysis is necessary for the recycling of cytosolic receptors. Ubiquitination also seems to be crucial for the export of PEX5 from peroxisome to the cytosol.



Evolutionary origins

The protein content in peroxysomes varies depending on the species or organism, but the presence of proteins common to many species has been used to suggest endosymbiotic origin; that is, peroxisomes evolved from bacteria that attacked larger cells as parasites and very gradually evolved in a symbiotic relationship. However, this view has been questioned by recent discoveries. For example, peroxisome-free mutants can restore peroxisomes after the introduction of the wild-type gene.


Two independent evolutionary analyzes of the peroxisomal proteome detected homology between the peroxisomal importing machinery and the ERAD pathway in the endoplasmic reticulum and a number of metabolic enzymes that were probably recruited from the mitochondria. Recently, it has been suggested that peroxisome may have had the cancerous origin, however, it is controversial.