Peroxisomes – the tiny organelles present inside the cells are pure magic. Did you know that without peroxisomes, we would literally fail to detox our body?
Did we get your attention? Alright then! Let us begin our journey of learning some mind-blowing peroxisome facts and find out what these cell organelles have in store for us.
Peroxisomes Facts: General Information
1. Peroxisomes are small, single-membrane (made of two layers of lipids) cell organelles.
3. The core of peroxisomes is dense and crystalline in most of the cells.
4. They are present in all eukaryotic cells including humans.
5. Each human cell has around 500 peroxisomes.
6. They lack DNA and ribosomes.
Peroxisomes Facts: History of Discovery
7. From mid-1950’s, electron microscopists have observed small bodies in cells and called them microbodies because of their size.
8. In 1954, J. Rhodin, a Swedesh doctoral student, was the first person to describe peroxisomes.
9. P. Baudbuin and C. De Duve coined the term “peroxisome” for the microbodies of mammalian system in 1966.
10. They even described the structure and functions of peroxisomes.
11. Tolbert’s group isolated leaf peroxisomes from spinach leaf in Michigan in 1968.
12. Beevers discovered glyoxylate cycle or glycolate cycle which contain glyoxysomes (special peroxisomes) in the endosperm (part of the seed which stores food for the developing plant embryo) of germinating castor beans in 1969.
13. It is to be noted that glyoxylate cycle or glycolate cycle takes place only in plants.
14. Biogenesis of peroxisomes has been studied by various cell biologists like Lazarrow and Purdue in 2001, Flynn, Mullen and Trelease in 2001, Dammai and Subramani in 2001, and Lazarrow in 2003.
Peroxisomes Facts: Occurrence
16. They are also prominent in algae, photosynthetic cells of plants and germinating seeds of those plant species which store fat in the seeds like corn, sunflower, soybean, peanut, pumpkin etc.
Peroxisomes Facts: Structure of the Organelle
17. Peroxisomes vary in shape and size but the usual shape is circular.
18. Most of the peroxisomes have a diameter of 0.2 µm to 1.5 µm (0.15 µm to 0.25 µm diameter is seen in most of the mammalian tissues).
19. The peroxisomes are bounded by a single membrane made up of protein and lipid molecules.
20. The matrix of peroxisomes is different in different species. For example, in festucoid grasses, matrix contains threads or fibrils, in other species it contains amorphous nucleoid or a dense inner core.
21. However, in most of the species the matrix of peroxisomes shows crystalloid structure.
Peroxisomes Facts: Chemical Composition
22. Both animal peroxisomes and plant peroxisomes usually have a crystalline core.
23. In animal peroxisomes, the core consists of urate oxidase enzyme in crystalline form and in plant peroxisomes, the core consists of catalase enzyme in crystalline form.
24. However, it is to be noted that the enzymes catalase and oxidase are present in both animal and plant peroxisomes.
25. Apart from the above-mentioned enzymes, there are near about 50 enzymes present in peroxisomes.
26. Peroxisomes may have different enzymes in different cells in a single organism (depending upon the function of the peroxisome in the particular cell).
27. Proteins of peroxisomes are produced by free ribosomes (that are not attached to the endoplasmic reticulum).
28. Then these proteins get imported into peroxisomes as completed polypeptide chains.
29. Peroxisomes adapt well to environmental conditions. For example: yeast generally grows on sugar. When it grows on sugar, peroxisomes in yeast cells are very few. But when the yeast grows on methanol, peroxisomes in yeast cells increase in number to oxidize methanol. When the yeast grows on fatty acids, cells tend to develop large peroxisomes which break down the fatty acids.
Peroxisomes Facts: Functions of the Organelle
Because of the presence of so many enzymes, peroxisomes have several functions which are:
Metabolism of Hydrogen peroxide
Detoxifying harmful compounds
Fatty acid oxidation
Metabolism of nitrogen containing compounds
Catabolism of unusual compounds
Activities of biosynthesis
Peroxisomes Facts: Metabolism of Hydrogen Peroxide
30. One of the biggest functions of peroxisome is the detoxification of hydrogen peroxide(H2O2).
31. It is interesting to note that H2O2 is produced by “oxidases” enzyme which is present in peroxisome.
32. Catalase reduces H2O2 to H2O.
33. Catalase is the most abundant protein in most of the peroxisomes.
34. It constitutes up to 15% of the total protein present in peroxisome.
35. Every molecule of H2O2 produced by oxidases is destroyed by catalase.
36. Peroxisome is not the only cell organelle to produce H2O2. Mitochondria, endoplasmic reticulum and enzymes like glutathione peroxidase produce H2O2.
— To deal with such huge amounts of H2O2, enzymes like superoxide dimutase come into play.
— A possible relationship has been stressed that free radicals and peroxides fasten aging. — These free radicals’ kind of act on DNA and try to alter it and fasten aging.
— Reducing compounds like vitamin E, superoxide dismutase etc. counter the effects of H2O2 and helps in keeping the cells healthy.
Peroxisomes Facts: Detoxifying Harmful Compounds
37. Catalase not only reduces H2O2 but also reduces compounds like formic acid (CH2O2), ethanol (C2H5OH), methanol (CH3OH), formaldehyde (CH2O), nitrites, phenols etc.
38. These compounds are extremely dangerous to cells.
39. Peroxisomes of kidney cells or renal cells and liver cells or hepatic cells play an important role in these detoxification reactions.
Peroxisomes Facts: Fatty Acid Oxidation
40. Peroxisomes of animal cells, plant cells and fungal cells oxidizes chains of fatty acids.
41. In animal cells, peroxisomes oxidize 25 to 50% of fatty acids.
42. Mitochondria oxidizes the rest of fatty acids.
43. In plant cells, peroxisomes oxidize 100% of fatty acids.
44. Peroxisomes oxidize long chain fatty acids (containing 16 to 20 carbons), very long chain fatty acids (containing 24 to 26 carbons) and even branched fatty acids.
45. Once the oxidation of the fatty acids (16 carbons or more) takes place in peroxisomes, the product is further oxidized by mitochondria.
46. Therefore, in animal cells, peroxisomes help in shortening the fatty acids but not breaking fatty acids.
47. Peroxisomes in plant and yeast cells break down the fatty acids completely.
Peroxisomes Facts: Metabolism of Nitrogen Containing Compounds
48. Urate oxidase is required by animals (except primates) to oxidize urate.
49. While oxidizing urate, H2O2 is created and is destroyed by catalase.
50. One of the enzymes of peroxisomes that play a role in metabolism of nitrogen is aminotransferase.
51. These enzymes help in the biosynthesis of nitrogen compounds (which are useful to our body) and in the degradation of nitrogenous compounds (which are harmful for the body).
Peroxisomes Facts: Catabolism of Unusual Compounds
52. When peroxisomal oxidases work, they end up creating some byproducts for which cells have no degrative pathways.
53. One such byproduct is D-amino acids. They are destroyed by catalase enzyme.
54. In fungal cells, peroxisomes degrade xenobiotics (chemical compounds which are alien or foreign to the organism).
55. Xenobiotics include alkanes, short-chain hydrocarbons which are present in petroleum and oil.
56. These fungi (which contain such enzymes which destroy oil and petrol) are useful in cleaning up the oil spills.
Peroxisomes Facts: Activities of Biosynthesis
57. Peroxisomes help in biosynthesis of lysine (an amino acid) and lipids.
58. In animal cells, dolicol and cholesterol are synthesized by endoplasmic reticulum and peroxisomes.
59. Peroxisomes in liver cells help in synthesis of bile acids (which are derived from cholesterol).
60. Bile acids are important for absorbing vitamin A and vitamin K (fat soluble vitamins) and for absorbing fats.
61. Plasmalogens (a group of phospholipids) are synthesized with the help of the enzymes of peroxisomes.
63. Deficiency of plasmalogens causes abnormalities in myelination (myelin sheath formation on dendrites of neurons).
64. It is one of the reasons why peroxisomal disorders lead to neurological disorders or neurological diseases.
65. Genetic disorders which cause skin disorder usually affect the functions of peroxisome.
66. Uric acid oxidase is a peroxisomal enzyme which oxidizes uric acid.
67. It is absent in humans and hence a disease named gout affects humans which is caused by the accumulation of uric acid.
Did You Know These Peroxisomes Facts?
68. Plant peroxisomes have a role to play in metabolism of nitrogen in root nodules and in photorespiration.
69. 25% of the alcohol we drink is oxidized by catalase.
Sources: 1. Wikipedia 2. Cell Biology by P. S. Verma and V. K. Agarwal, Chapter 25 Peroxisomes, Page Number 520 to 528. 3. Wikipedia
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