Microbodies: Peroxisomes [With MCQs]

by

Microbodies: Peroxisomes

Peroxisomes come from the fundamental equipment of the eukaryotic cell and therefore occur in animals, plants, and fungi. Peroxisomes are introduced as common, single-membrane-bound subcellular organelles that have a fine granular matrix and carry out important metabolic functions in hydrogen peroxide and lipid metabolic process and are therefore necessary for human health and development.

They are present in all photosynthetic cells of higher plants in etiolated leaf tissue, in coleoptiles and hypocotyls, in tobacco stem and callus, in ripening pear fruits, and also in Euglenophyta, Protozoa, brown algae, fungi, liverworts, mosses, and ferns.

Table of Contents Hide
Nomenclature of Peroxisomes

Microbodies were first reported at the ultrastructural level in the proximal complicated tubule of mouse kidneys by Rhodin in 1954. This morphological classification was slowly replaced by the practical term ‘peroxisome’, which was introduced in 1965 by Christian De Duve.

Shape and Structure of Peroxisomes

Peroxisomes are organelles that can differ in shape, size, and number depending upon the energy requirements of the cell. In yeast cells, a carbohydrate-rich development medium shrinks peroxisomes. On the other hand, the existence of toxins or a lipid-rich diet plan can increase their number and size.

These organelles are made from a phospholipid bilayer with many membrane-bound proteins– especially those that function as protein transporters and translocators. The enzymes involved in detoxing and lipid metabolism are synthesized on totally free ribosomes in the cytoplasm and selectively imported into peroxisomes, making them more comparable to mitochondria and chloroplasts when compared to lysosomes that bud off from the endoplasmic reticulum (ER). Nevertheless, there is likewise some evidence connecting ER-mediated protein synthesis to the enzymes present in peroxisomes.

Peroxisomes and Lysosomes

Peroxisomes have some structural similarities with various organelles within the cell. Initially, it was tough to even distinguish lysosomes from peroxisomes through tiny evaluation alone. Afterward, differential centrifugation exposed that these two subcellular structures had different compositions.

Peroxisomes and Mitochondria

Peroxisomes share some similarities with mitochondria and chloroplasts. The majority of the proteins of these organelles are equated on complimentary ribosomes in the cytoplasm. However, unlike mitochondria and chloroplasts, peroxisomes contain no genetic material or translation machinery, for that reason, their whole proteome comes through import from the cytoplasm.

Functions of Peroxisomes

Studies show that peroxisomes contain at least 50 different types of enzymes for various biochemical pathways depending on the type of cell. Peroxisomes thought to carry out oxidation reactions that led to the production of hydrogen peroxide. As the hydrogen peroxide is harmful to the livings or cells, so peroxisomes also contain enzyme catalase which converts hydrogen peroxide to water or uses it for the oxidation of any other compound in cells.

Further Reading:  Zoogeographical Realm – The Oriental Region

Peroxisomes perform the following types of bioactivities:

Hydrogen Peroxide Metabolism

As discussed earlier, peroxisomes are called peroxisomes, because they contain more than one enzyme. For example, D amino acid oxidase and urate oxidase use molecular oxygen to remove hydrogen atoms from compounds during oxidation reaction and form hydrogen peroxide.

Catalase that makes up 40 % of the total protein of peroxisomes, uses this hydrogen peroxide and oxidizes other organic compounds like alcohols, phenols, etc. In animal cells, peroxisomes are the sites for some quantity of lipid biogenesis, specifically of unique phospholipids called plasmalogens that form the myelin sheath in nerve fibers. Peroxisomes are likewise necessary for the synthesis of bile salts.

These types of oxidation reactions are necessary for the detoxification and removal of toxic wastes from the blood and hence make them a vital part of cells in the kidney and liver.

Glycolate cycle

In plants, peroxisomes contain catalase in addition to other enzymes of the glycolate pathway. The glycolate pathway forms the amino acids glycine and serine from the non-phosphorylated intermediates of the photosynthetic carbon reduction cycle. This cycle also involves the formation of precursors for nucleic acid synthesis.

Photorespiration

The most popular role of peroxisomes in photosynthetic plant tissues is their participation in photorespiration, a procedure likewise known as the oxidative C2 cycle or the oxidative photosynthetic carbon cycle. Photorespiration is a necessary process in land plants. The pathway is highly compartmentalized and includes reactions in chloroplasts, peroxisomes, and mitochondria.

MCQs about Microbodies

  • Which organelles are peroxisomes found in?
    • a) Animals only
    • b) Plants only
    • c) Fungi only
    • d) Animals, plants, and fungi
    • Answer: d) Animals, plants, and fungi
  • Who introduced the term ‘peroxisome’ in 1965?
    • a) Rhodin
    • b) Christian De Duve
    • c) Mendel
    • d) Watson and Crick
    • Answer: b) Christian De Duve
  • What determines the shape, size, and number of peroxisomes in a cell?
  • Which type of medium causes peroxisomes in yeast cells to shrink?
    • a) Carbohydrate-rich
    • b) Protein-rich
    • c) Lipid-rich
    • d) Salt-rich
    • Answer: a) Carbohydrate-rich
  • Which type of ribosomes synthesize enzymes involved in detoxing and lipid metabolism for peroxisomes?
    • a) Bound ribosomes
    • b) Free ribosomes
    • c) Mitochondrial ribosomes
    • d) Chloroplastic ribosomes
    • Answer: b) Free ribosomes
  • What enzyme in peroxisomes converts hydrogen peroxide to water?
    • a) Catalase
    • b) Peroxidase
    • c) Dehydrogenase
    • d) Oxidase
    • Answer: a) Catalase
  • Which type of reactions are essential for the detoxification and removal of toxic wastes from the blood?
    • a) Reduction reactions
    • b) Hydrolysis reactions
    • c) Oxidation reactions
    • d) Polymerization reactions
    • Answer: c) Oxidation reactions
  • What percentage of the total protein of peroxisomes does catalase make up?
    • a) 10%
    • b) 20%
    • c) 30%
    • d) 40%
    • Answer: d) 40%
  • What type of cycle involves the formation of amino acids glycine and serine in plants?
    • a) Citric acid cycle
    • b) Glycolysis
    • c) Glycolate cycle
    • d) Krebs cycle
    • Answer: c) Glycolate cycle
  • What is another name for the process of photorespiration?
    • a) Calvin cycle
    • b) Krebs cycle
    • c) Glycolysis
    • d) Oxidative C2 cycle
    • Answer: d) Oxidative C2 cycle
  • What is the main function of peroxisomes in hydrogen peroxide metabolism?
    • a) Production of hydrogen peroxide
    • b) Storage of hydrogen peroxide
    • c) Conversion of hydrogen peroxide to water
    • d) Destruction of other organelles
    • Answer: c) Conversion of hydrogen peroxide to water
  • Which type of cells contain peroxisomes that are crucial for the synthesis of bile salts?
    • a) Liver cells
    • b) Muscle cells
    • c) Nerve cells
    • d) Skin cells
    • Answer: a) Liver cells
  • What is the primary role of peroxisomes in the glycolate cycle?
    • a) Formation of glucose
    • b) Formation of amino acids glycine and serine
    • c) Formation of ATP
    • d) Formation of lipids
    • Answer: b) Formation of amino acids glycine and serine
  • In which tissues do peroxisomes primarily participate in photorespiration?
    • a) Nerve tissues
    • b) Muscle tissues
    • c) Photosynthetic plant tissues
    • d) Connective tissues
    • Answer: c) Photosynthetic plant tissues
  • What is the alternative name for the oxidative C2 cycle?
    • a) Calvin cycle
    • b) Krebs cycle
    • c) Glycolysis
    • d) Photorespiration
    • Answer: d) Photorespiration
  • Which organelle is NOT mentioned to share structural similarities with peroxisomes?
    • a) Lysosomes
    • b) Mitochondria
    • c) Chloroplasts
    • d) Nucleus
    • Answer: d) Nucleus
  • What is the function of the enzymes synthesized in peroxisomes on free ribosomes?
    • a) Act as catalysts for reactions in the cytoplasm
    • b) Synthesize proteins for the cell membrane
    • c) Detoxification and lipid metabolism
    • d) Produce ATP for cellular energy
    • Answer: c) Detoxification and lipid metabolism
  • Which organelle’s proteome is entirely imported from the cytoplasm?
    • a) Mitochondria
    • b) Chloroplasts
    • c) Lysosomes
    • d) Peroxisomes
    • Answer: d) Peroxisomes
  • What is the main biochemical pathway associated with peroxisomes in animal cells?
    • a) Glycolysis
    • b) Krebs cycle
    • c) Lipid biogenesis
    • d) Protein synthesis
    • Answer: c) Lipid biogenesis
  • Which organelle is necessary for the formation of myelin sheath in nerve fibers?
    • a) Mitochondria
    • b) Chloroplasts
    • c) Peroxisomes
    • d) Lysosomes
    • Answer: c) Peroxisomes
  • What is the primary role of peroxisomes in detoxification within the cell?
    • a) Production of toxins
    • b) Storage of toxins
    • c) Oxidation reactions leading to detoxification
    • d) Inhibition of detoxification enzymes
    • Answer: c) Oxidation reactions leading to detoxification
Further Reading:  Human Eye - Structure and Disorders of the Eye

 

Summary: Understanding Peroxisomes

In this tutorial, we embarked on a comprehensive journey into the world of peroxisomes, pivotal organelles that play vital roles in the metabolism and maintenance of eukaryotic cells. Below is a synopsis of the key concepts covered:

Introduction to Peroxisomes:

Peroxisomes, ubiquitous in animals, plants, and fungi, were introduced as essential, single-membrane-bound organelles with a granular matrix. Their presence spans a wide range of organisms, emphasizing their significance in various biological processes.

Nomenclature and Morphology:

We explored the historical development of peroxisome nomenclature, tracing back to their discovery by Rhodin in 1954 and the subsequent introduction of the term ‘peroxisome’ by Christian De Duve in 1965. Additionally, we examined the morphological diversity of peroxisomes, shaped and sized according to cellular energy demands.

Structural Features:

Peroxisomes were elucidated as phospholipid bilayer structures, housing numerous membrane-bound proteins involved in transport and translocation. The mechanisms of enzyme synthesis and import from cytoplasmic ribosomes were discussed, drawing parallels with other organelles like mitochondria and chloroplasts.

Further Reading:  Morphological Character and Types of Roots

Functional Insights:

We delved into the multifaceted functions of peroxisomes, focusing on their pivotal roles in hydrogen peroxide metabolism, lipid biogenesis, and detoxification pathways. The significance of enzyme catalase in converting hydrogen peroxide into water and other organic compounds underscored the importance of peroxisomes in cellular homeostasis.

Specialized Pathways:

Furthermore, we explored specialized pathways associated with peroxisomes, including the glycolate cycle in plants and their involvement in photorespiration. These pathways highlighted the versatility of peroxisomes in orchestrating complex biochemical reactions crucial for cellular function.

Conclusion:

In conclusion, this tutorial provided a comprehensive understanding of peroxisomes, shedding light on their structural diversity, functional significance, and intricate biochemical pathways. By unraveling the mysteries of peroxisomes, we gain deeper insights into the fundamental mechanisms driving cellular metabolism and homeostasis.

You may also like to learn: