Peroxisomes: Definition, Structure, Diagram & Functions

Peroxisomes are membrane-bound organelles found in the cytoplasm of eukaryotic cells. They are small vesicles that contain digestive and oxidative enzymes. Peroxisomes are involved in various metabolic processes, particularly those related to lipid metabolism and detoxification.

It is made of a phospholipid bilayer with a fine granular matrix, which contains a variety of enzymes that carry out various metabolic processes. In this article, we will study peroxisomes, their structure with a well-labeled diagram, and the functions of peroxisomes in detail.

Peroxisomes Definition

Peroxisomes are small membrane-bound vesicles found in the cytoplasm of eukaryotic cells that are involved in lipid metabolism, energy metabolism, and chemical detoxification.

What are Peroxisomes?

Peroxisomes were discovered by the Belgian cell biologist Christian de Duve in 1967 in liver cells and named them peroxisomes, replacing the previously used term “microbodies”. Peroxisomes are membrane-bound vesicles that contain digestive enzymes and oxidative enzymes. These enzymes carry out several metabolic reactions, including energy metabolism, lipid metabolism, and detoxification. It also helps in maintaining cellular homeostasis. Peroxisomes got their name based on their involvement in generating and scavenging hydrogen peroxide activities. A human cell contains around 102–103 peroxisomes in the cytoplasm. Their dysfunction can lead to severe genetic disorders that can affect multiple aspects of metabolism.

Peroxisomes Diagram

A diagram of peroxisome is shown below:

Peroxisomes Structure

Peroxisomes are small membrane-bound cellular organelles that range in size from 0.1–1 µm diameter. They are involved in a variety of metabolic reactions, including lipid and energy metabolism. The structure of the peroxisomes is as follows:

• The number, size, shape and protein composition of peroxisomes varies. It depends on cell type and environmental conditions.
• Membrane: Peroxisome membrane is made of a phospholipid bilayer. It consists of two layers of fat molecules and proteins that allow contents to move in and out of the cell.
• Matrix: Peroxisomes are circular in cross section and contain fine granular matrix. The matrix of a peroxisome is made up of fibrils or a crystalloid structure that contains enzymes.
• Enzymes: There are around 60 known enzymes present in the matrix of the peroxisomes. The main enzymes present are urate oxidase, D-amino acid oxidase and catalase. These enzymes are responsible for break down of hydrogen peroxide into water and oxygen.
• Compartmentalization within peroxisomes provides an optimized environment to carry out various metabolic reactions within it. It is required to sustain various cellular functions and viability of the organism.
• Peroxisomes are found in close association of ER, mitochondria or chloroplast within the cell.
• Peroxisomes lacks DNA and proteins are transported after translation from the cytosol.

Peroxisome Functions

Peroxiosme are responsible for carrying out various metabolic processes like lipid metabolism, energy metabolism and detoxification. Some of the important functions of the peroxisomes are discussed as follows:

• Beta-Oxidation of Fatty Acids: Peroxisome break down long-chain fatty acids through beta-oxidation into acetyl-CoA, which can be utilized for production of energy.
• Hydrogen Peroxide Metabolism: Enzyme catalase present in the peroxisome breaks down hydrogen peroxide into water and oxygen. It help in the detoxification of hydrogen peroxide.
• Glyoxylate Cycle: It occurs in plants and some microorganisms. Glyoxylate cycle enzymes are located both inside and outside the peroxisome. The glyoxylate cycle occurs in peroxisomes where the conversion of fatty acids into carbohydrates take place.
• Lipid biosynthesis: Synthesis of lipid such as cholesterol and dolichol occurs in peroxisomes.
• Plasmalogen: Plasmalogen is a type of phospholipid that is synthesised by the peroxisomes. It is essential for maintaining the structure and function of cell membranes.
• Seed Germination: Peroxisomes present in seeds is responsible for the conversion of stored fatty acids to carbohydrates. It provides raw material and energy for the growth of germinating plants.
• Photorespiration: Peroxisome along with cholorplast carry out photorespiration in the leaves.
• Degradation of purines: Enzymes present in the peroxisome especially uric acid oxidase carry out the catabolism of purines, polyamines and amino acids.
• Bioluminescence: Enzyme Luciferase present in the peroxisomes of fireflies help in bioluminescence. It helps the flies in finding its meal or mate.

Metabolism of Peroxisomes

Peroxisomes are small subcellular organelle that contain enzymes responsible for several metabolic processes. These processes include: 

• One of their primary function is lipid metabolism where long-chain fatty acids breaks down into acetyl CoA.
  • β-oxidation
  • α-oxidation
  • Ether phospholipid synthesis
  • Isoprenoid biosynthesis
• Reactive oxygen species metabolism
• Bile acid synthesis
• Peroxisomes are involved in the detoxification of harmful substances through processes such as the breakdown of hydrogen peroxide into water and oxygen

Overall, peroxisomes contribute significantly to cellular metabolism by participating in key biochemical pathways that impact energy production, lipid metabolism, and detoxification.

Peroxisomal Disorders

Peroxisomal disorders are type of genetic diseases that affect one or more peroxisomal functions. Disorders are characterised by abnormal oxidation and toxic accumulation of very long-chain fatty acid. Common peroxisomal disorders include:

• Zellweger syndrome
• Neonatal adrenoleukodystrophy
• Infantile Refsum disease
• Phytanic acid accumulation

Some common symptoms of the diseases includes: Hearing and vision loss, Hypotonia, Neurological issues, seizures,  Adrenal insufficiency issues, Liver, kidney and bone diseases. Treatment include only supportive care and symptom alleviation as there is no cure.

Difference Between Peroxisome and Lysosomes

The differences between peroxisome and lysosomes are as follows:

Also Read:

• Structure and Functions of Microbodies
• Plant Cell – Definition, Diagram, Structure, & Functions
• Endomembrane System – Overview, Structure, and Functions

FAQs on Peroxisomes

What is the Main Function of Peroxisomes?

The primary function of the peroxiosme is to carry out beta oxidation of the fatty acid, lipid metabolism, processing of reactive oxygen species and catabolism of D-amino acids, polyamines, and bile acids.

Where are Peroxisomes Found in the Cell?

Peroxisomes are small membrane bound organelles found in the cytoplasm of the eukaryotic cells. They contain at least 50 enzymes.

What are the Differences Between Lysosomes and Peroxisomes?

Peroxisomes are involved in lipid metabolism, detoxification, and the breakdown of hydrogen peroxide while Lysosomes are involved in cellular waste digestion and material recycling, containing digestive enzymes.

What are Peroxisomes Formed by?

Peroxisomes are formed by the following processes: Synthesis of membrane proteins and lipids, Selective import of proteins from the cytosol and Growth and division of the resulting organelles.

What are the Characteristics of Peroxisomes?

Peroxisomes are small membrane bound organelles that contain fine granular matrix. They are spherical structures with a phospholipid bilayer and contains various enzymes for metabolic processes.

What is an Example of a Peroxisome?

Some example of peroxisomes includes Yeast cells grown on sugar have small peroxisomes, Peroxisomes in liver cells remove hydrogen from alcohol and attach it to oxygen to create hydrogen peroxide.

What is the Difference Between Mitochondria and Peroxisomes?

Peroxisomes and mitochondria are different organelles within eukaryotic cells. Peroxisomes are involved in fatty acid metabolism and detoxification, while mitochondria generate ATP through cellular respiration.

What is the Structure of Peroxisome?

Peroxisomes are small organelles (0.1–1 µm in diameter) found in the cytoplasm of a cell. They are made up of a single lipid bilayer that surrounds a granular, protein-rich matrix.

What are Two Diseases of Peroxisomes?

Peroxisomal diseases are a group of metabolic diseases that are caused by the dysfunction of peroxisomes. Some examples include Zellweger syndrome, Infantile Refsum’s disease and Adrenoleukodystrophy.

Which Organ has More Peroxisomes?

Liver and Kidney contains the highest density of the peroxisomes as they are involved in toxin removal and waste filtration.