Peroxisomes

What are Peroxisomes?

Peroxisomes are small vesicles, single membrane-bound organelles found in the eukaryotic cells. They contain digestive enzymes for breaking down toxic materials in the cell and oxidative enzymes for metabolic activity. They are a heterogeneous group of organelles and the presence of the marker enzymes distinguished them from other cell organelles.

Peroxisomes play an important role in lipid production and are also involved in the conversion of reactive oxygen species such as hydrogen peroxide into safer molecules like water and oxygen by the enzyme catalase.

Mostly peroxisomes occur as an individual organelle, e.g. in fibroblasts. They also exist in the form of interconnected tubules in liver cells known as peroxisome reticulum.

Also read: Lysosomes

Peroxisome Structure

Peroxisomes vary in shape, size and number depending upon the energy requirements of the cell. These are made of a phospholipid bilayer with many membrane-bound proteins.

The enzymes involved in lipid metabolism are synthesised on free ribosomes and selectively imported to peroxisomes. These enzymes include one of the two signalling sequences- Peroxisome Target Sequence 1 being the most common one.

The phospholipids of peroxisomes are usually synthesised in smooth Endoplasmic reticulum. Due to the ingress of proteins and lipids, the peroxisome grows in size and divides into two organelles.

Peroxisomes do not have their own DNA. Proteins are transported from the cytosol after translation.

Peroxisome Function

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

• They take part in various oxidative processes.
• They take part in lipid metabolism and catabolism of D-amino acids, polyamines and bile acids.
• The reactive oxygen species such as peroxides produced in the process is converted to water by various enzymes like peroxidase and catalase.
• In plants, peroxisomes facilitate photosynthesis and seed germination. They prevent loss of energy during photosynthesis carbon fixation.

Metabolism of Peroxisomes

Isolated peroxisomes are permeable to small molecules such as sucrose. During the 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.

Also read: Nucleus

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