- Key People:
- Christian René de Duve
- Related Topics:
- Zellweger syndrome
- Organelle
- peroxisomal disorder
peroxisome
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What is a peroxisome?
Peroxisomes are membrane-bound organelles in the cytoplasm of eukaryotic cells. They contain enzymes that oxidize molecules, producing hydrogen peroxide, which is converted into water and oxygen by catalase, neutralizing its toxicity.
Peroxisomes play a key role in oxidizing specific biomolecules and contribute to the biosynthesis of membrane lipids known as plasmalogens. In plant cells, they recycle carbon during photorespiration, with glyoxysomes converting fatty acids to carbohydrates. Peroxisomal disorders, caused by gene mutations, can lead to severe conditions like Zellweger syndrome.
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Where are peroxisomes found in a cell?
Peroxisomes are membrane-bound organelles found in the cytoplasm of eukaryotic cells. These organelles contain enzymes that oxidize molecules, producing hydrogen peroxide, which is converted into water and oxygen by catalase, neutralizing its toxicity. In plant cells, specialized peroxisomes called glyoxysomes convert fatty acids to carbohydrates. Peroxisomes play a key role in the oxidation of biomolecules and contribute to the biosynthesis of membrane lipids.
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What is the main function of peroxisomes?
Peroxisomes are membrane-bound organelles in the cytoplasm of eukaryotic cells that play a crucial role in oxidation of biomolecules and biosynthesis of membrane lipids. They contain enzymes that oxidize molecules, producing hydrogen peroxide, which is toxic to the cell. Peroxisomes also contain enzymes like catalase to convert hydrogen peroxide into water and oxygen, neutralizing the toxicity. In plant cells, peroxisomes recycle carbon during photorespiration and convert fatty acids to carbohydrates.
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How do peroxisomes help protect the cell from damage?
Peroxisomes protect cells from damage by safely oxidizing specific molecules like fatty acids and amino acids. This oxidation produces hydrogen peroxide, which is toxic because it can react with other molecules. However, peroxisomes contain enzymes such as catalase that convert hydrogen peroxide into water and oxygen, neutralizing the toxicity. Byproduct detoxification within the peroxisomes ensures that the rest of the cell is not exposed to the harmful effects of hydrogen peroxide, thus preventing damage.
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What substances do peroxisomes break down or produce?
Peroxisomes are organelles in eukaryotic cells that play a crucial role in oxidation reactions. They break down specific biomolecules, especially fatty acids and amino acids. These reactions produce hydrogen peroxide, which peroxisomes neutralize into water and oxygen using enzymes like catalase. Peroxisomes also contribute to the biosynthesis of membrane lipids known as plasmalogens. In plant cells, peroxisomes recycle carbon from phosphoglycolate during photorespiration, and glyoxysomes convert fatty acids to carbohydrates.
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How do peroxisomal disorders affect human health?
Peroxisomal disorders, stemming from mutated genes, disrupt peroxisome function, causing a range of health issues. These congenital conditions vary in severity, from moderate to severe.
In conditions like Zellweger syndrome, the absence or reduction of peroxisomes leads to the accumulation of very-long-chain fatty acids, copper, and iron in the blood and tissues. Infants may be born with facial deformities, intellectual disabilities, and impaired vision and hearing.
Other disorders, such as X-linked adrenoleukodystrophy (X-ALD), can cause neurological issues, behavioral problems, and loss of speech and motor skills. Though there is no specific treatment, bone marrow transplantation has shown some success if done early.
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peroxisome, membrane-bound organelle occurring in the cytoplasm of eukaryotic cells. Peroxisomes play a key role in the oxidation of specific biomolecules. They also contribute to the biosynthesis of membrane lipids known as plasmalogens. In plant cells, peroxisomes carry out additional functions, including the recycling of carbon from phosphoglycolate during photorespiration. Specialized types of peroxisomes have been identified in plants, among them the glyoxysome, which functions in the conversion of fatty acids to carbohydrates.
Peroxisomes contain enzymes that oxidize certain molecules normally found in the cell, notably fatty acids and amino acids. Those oxidation reactions produce hydrogen peroxide, which is the basis of the name peroxisome. However, hydrogen peroxide is potentially toxic to the cell, because it has the ability to react with many other molecules. Therefore, peroxisomes also contain enzymes such as catalase that convert hydrogen peroxide to water and oxygen, thereby neutralizing the toxicity. In that way peroxisomes provide a safe location for the oxidative metabolism of certain molecules.
Plasmalogens are the primary ether lipids in humans (ether lipids contain one or more ether linkages, distinguishing them from other lipids, which typically contain ester linkages). Specialized enzymes in peroxisomes catalyze the synthesis of an ether phospholipid precursor. The precursor molecule undergoes further synthesis in the endoplasmic reticulum, resulting in the production of plasmalogen. Although the physiological role of plasmalogens is unclear, defects in their biosynthesis, which occur as a result of peroxisomal disorders, are associated with severe developmental conditions, including rhizomelic chondrodysplasia punctata (RCDP) and Zellweger syndrome. In the brain reduced levels of plasmalogens have been observed in patients with Alzheimer disease and linked to deficits in cognitive function.
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Peroxisomal disorders are caused by mutations in genes that are involved in peroxisome biogenesis or that encode the enzymes and transporter proteins (which take up the enzymes from the cytoplasm) of the peroxisome. Peroxisomal disorders are congenital disorders, and they range from relatively moderate to severe in nature. The Zellweger spectrum, for example, includes Zellweger syndrome, neonatal adrenoleukodystrophy (NALD), and infantile Refsum disease. Zellweger syndrome is characterized by complete absence or reduction in the number of peroxisomes. It is the most severe condition within the Zellweger syndrome. Mutations giving rise to Zellweger syndrome cause copper, iron, and substances called very long chain fatty acids to accumulate in the blood and in tissues, such as the liver, brain, and kidneys. Infants with Zellweger syndrome are often born with facial deformity and intellectual disability; some may have impaired vision and hearing and may experience severe gastrointestinal bleeding or liver failure. Prognosis is poor: most infants with Zellweger syndrome do not live beyond one year. Symptoms of NALD and infantile Refsum disease, by contrast, appear in late infancy or in childhood, and patients may survive to early adulthood. Likewise, patients with RCDP may survive into childhood or, in mild cases, early adulthood.
Peroxisomes were described in 1960 as part of the pioneering work of Christian René de Duve, who developed cell fractionation techniques. De Duve’s method separated organelles on the basis of their sedimentation and density properties, and peroxisomes are denser than other organelles. He later coined the term peroxisome. De Duve shared the 1974 Nobel Prize for Physiology or Medicine with Albert Claude and George Palade for that work.