Peroxisome - Basics

Basics only

A variety of small cellular components bounded by single membrane found in Plant and
animal cell. Microbodies are of two types; Peroxisomes and glyoxysomes

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PEROXISOMES
MICROBODIES or MICROSOMES
 A variety of small cellular components bounded by single membrane found in Plant and
animal cell. Microbodies are of two types; Peroxisomes and glyoxysomes

PEROXISOMES
 Peroxisomes are membrane-bound organelles in most eukaryotic cells, primarily
involved in lipid metabolism and the conversion of reactive oxygen species (ROS) such
as hydrogen peroxide into safer molecules like water and oxygen.
 It was identified as organelles by Belgian cytologist Christian de Duve in 1967.
 Peroxisomes lack DNA; peroxisomal proteins are encoded in nuclear DNA and
posttranslationally enter the organelle.
 Peroxisomes originate from the ENDOPLASMIC RETICULUM, divide, and are
degraded through pexophagy (a form of organelle-specific autophagy)
 They are found floating freely in the cytoplasm in close association of ER,
mitochondria or chloroplast within the cell.
 Peroxisomes are among the simplest of eukaryotic organelles.
 Peroxisomes are most abundantly found in detoxifying organs such as the liver and
kidney cells.

ULTRASTRUCTURE AND COMPOSITION
 Peroxisomes are organelles that can vary in shape, size and number depending on
the energy needs of the cell. In yeast cells, a carbohydrate-rich growth medium shrinks
peroxisomes. On the other hand, the presence of toxins or a lipid-rich diet can increase their number and
size.
 They are usually circular in cross-section.
 These organelles are made of a phospholipid bilayer (7nm) with many membrane -
bound proteins – especially those that act as protein transporters and translocators
 Peroxisomes 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.
 It consists of a single limiting membrane of lipid and protein molecules enclosing the
granular matrix.
 The matrix consists of fibrils or with a crystalloid structure containing enzymes.
 Approximately 60 known enzymes are present in the matrix of peroxisomes.
 The main groups of enzymes include:
1. Urate oxidase
2. D-amino acid oxidase
3. Catalase
4. Peroxidase
 They exist either in the form of a network of interconnected tubules called
peroxisome reticulum or as individual microperoxisomes.

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FUNCTIONS OF PEROXISOMES
They play important roles in metabolism, reactive oxygen species detoxification, and
signaling.
1. Hydrogen Peroxide Metabolism:
Peroxisomes have developed to a point where they are able to contain that hydrogen
peroxide and break it down into water (H2O) and oxygen (O2). The water is harmless to
the cell and the oxygen can be used in the next digestive reaction.

Hydrogen peroxidase
H2O2 H2O + O2
Hydrogen peroxide water oxygen

2. Fatty acid oxidation:
Peroxisomes mostly deal with β–oxidation of fatty acids, the mobilization of lipid stores
in seeds.

3. 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 component for tissues of heart and brain.

4. Germination of seeds
Peroxisomes in seeds are responsible for the conversion of stored fatty acids to
carbohydrates, critical for providing the energy and raw materials for the growth of
germinating plant.

5. Photorespiration
peroxisomal enzymes enable photorespiration, which increases photosynthetic
efficiency. Peroxisomes contribute to the synthesis of critical signaling molecules
including auxin, and salicylic acid phytohormones.

6. Degradation of purines
Catabolism of purines, polyamines and amino acids especially by uric acid oxidase
7. Bioluminescence
Luciferase enzyme found in the peroxisomes of fireflies help in bioluminescence and
thus aids the flies in finding a mate or its meal.
8. They also play a part in the way organisms digest alcohol (ethanol).