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- Peroxisomes are small, membrane-enclosed cellular organelles containing oxidative enzymes that are involved in a variety of metabolic reactions, including several aspects of energy metabolism.
- They are considered as an important type of microbody found in both plants and animal cells.
- They were identified as organelles by Belgian cytologist Christian de Duve in 1967 after already been described.
- First peroxisomes to be discovered were isolated from leaf homogenate of spinach.
- They are most abundantly found in detoxifying organs such as the liver and kidney cells. However, they can be induced to proliferate in response to metabolic needs.
Structure of Peroxisomes
- They are membrane-bound spherical bodies of 0.2 to 1.5 μm in diameter found in all eukaryotic organisms including both plants and animal cells.
- They are found floating freely in the cytoplasm in close association of ER, mitochondria or chloroplast within the cell.
- They are among the simplest of eukaryotic organelles.
- They exist either in the form of a network of interconnected tubules called peroxisome reticulum or as individual microperoxisomes.
- They are variable in size and shape according to the cell and usually circular in cross-section.
- They range from 0.2 -1.5 μm in diameter.
- It consists of a single limiting membrane of lipid and protein molecules enclosing the granular matrix.
- The matrix consists of fibrils or a crystalloid structure containing enzymes.
- Approximately 60 known enzymes are present in the matrix of peroxisomes.
- They are responsible to carry out oxidation reactions leading to the production of hydrogen peroxide.
- The main groups of enzymes include:
- Urate oxidase
- D-amino acid oxidase
Functions of Peroxisomes
- Hydrogen Peroxide Metabolism:
- Enzymes present in the peroxisomes both lead to the production and elimination of H202 which is a reactive oxygen species.
- Fatty acid oxidation:
- Oxidation of fatty acids, in animal cells, occurs in both peroxisomes and mitochondria, but in yeasts and plants, only limited to peroxisomes.
- Oxidation is accompanied by the production of H202 which is decomposed by catalase enzyme. This provides a major source of metabolic energy.
- Lipid biosynthesis
- Synthesis of cholesterol and dolichol occurs in both ER and peroxisomes. Bile acid synthesis takes place from cholesterol in the liver.
- Peroxisomes contain enzymes to synthesize plasmalogens, a family of phospholipids which are important membrane components of tissues of the heart and brain.
- Germination of seeds
- Peroxisomes in seeds responsible for the conversion of stored fatty acids to carbohydrates, critical to providing energy and raw materials for the growth of germinating plants.
- Peroxisomes in leaves particularly in the green ones carry out the photorespiration process along with chloroplasts.
- Degradation of purines
- Carry out the catabolism of purines, polyamines and amino acids especially by uric acid oxidase
- Luciferase enzyme found in the peroxisomes of fireflies help in bioluminescence and thus aid the flies in finding a mate or its meal.
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- Kar,D.K. and halder,S. (2015). Cell biology genetics and molecular biology.kolkata, New central book agency
- R and suwal,S.N. (2010).Human Anatomy and physiology. Kathmandu, vidyarthi prakashan (p.) ltd.
Peroxisomes- Definition, Structure, Functions, and Diagram