Peroxisomes

peroxisomes

What are Peroxisomes?

Peroxisomes are small vesicles, single membrane-bound organelles found around the eukaryotic cells. They contains digestive enzymes for breaking down toxic materials in the cell and oxidative enzymes for metabolic activity.Peroxisomes play an important role in lipid production and also involved in the conversion of reactive oxygen species such as hydrogen peroxide into safer molecules like water and oxygen.

Peroxisomes are a heterogeneous group of organelles and the presence of the marker enzymes distinguished them from other cell organelles. The peroxisome derives its name from the fact that many metabolic enzymes that generate hydrogen peroxide as a by-product are sequestered here because peroxides are toxic to cells. Within peroxisomes, hydrogen peroxide is degraded by the enzyme catalase to water and oxygen. Peroxisomes are surrounded by a single membrane and they range in the diameter from 0.1 to 1 mm. They exist either in the form of a network of interconnected tubules (peroxisome reticulum), as in liver cells, or as individual micro peroxisomes in other cells such as tissue culture fibroblasts.

Metabolism of Peroxisomes

Isolated peroxisomes are permeable to small molecules such as sucrose. During isolation process, they often lose proteins that are normally confined to the peroxisomal matrix. In all living cells, peroxisomes are the sealed vesicles surrounded by a single membrane.

Functions of Peroxisomes

The main function of peroxisomes is the lipid metabolism and the processing of reactive oxygen species. Other functions include:

  • The synthesis of ether glycerolipids or plasmalogens.
  • The formation of bile acids, dolichol, and cholesterol.
  • The catabolism of purines, polyamines, and amino acids, and the detoxification of reactive oxygen species
  • In methylotrophic yeasts, peroxisomes are also involved in the metabolism of methanol and methylamines.

Biogenesis of Peroxisomes

As peroxisomes have no DNA, all their proteins must be imported from genes encoded in the nucleus. Most of the proteins that reside in the peroxisome matrix and membrane are synthesized in the cytosol and then imported posttranslationally to the organelle. About 25 PEX genes, encoding proteins called peroxins are necessary for the biogenesis of the organelle. Most of these genes are found in multiple organisms and 13 are conserved in humans.

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Practise This Question

Which of these statements best explains the method by which enzymes catalyze a chemical reaction?