Lecture 14 - Microbodies | Cell Biology- Botany PDF Download

 Page 1


Microbodies 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
 
 
 
 
Lesson: Microbodies 
Lesson Developer: Geetika Kalra 
College/Department:ANDC, University of Delhi 
  
Page 2


Microbodies 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
 
 
 
 
Lesson: Microbodies 
Lesson Developer: Geetika Kalra 
College/Department:ANDC, University of Delhi 
  
Microbodies 
Institute of Lifelong Learning, University of Delhi 1 
 
Table of Contents       
 
Chapter: Microbodies                                                        
? Introduction  
? Peroxisomes  
? Structure 
? Functions 
? Fatty acid ß-oxidation 
? Role of peroxisome in photorespiration 
? Conversion of fixed nitrogen to nitrogen-rich 
organic compounds 
? Other functions 
? Biogenesis 
? Peroxisome assembly 
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
Page 3


Microbodies 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
 
 
 
 
Lesson: Microbodies 
Lesson Developer: Geetika Kalra 
College/Department:ANDC, University of Delhi 
  
Microbodies 
Institute of Lifelong Learning, University of Delhi 1 
 
Table of Contents       
 
Chapter: Microbodies                                                        
? Introduction  
? Peroxisomes  
? Structure 
? Functions 
? Fatty acid ß-oxidation 
? Role of peroxisome in photorespiration 
? Conversion of fixed nitrogen to nitrogen-rich 
organic compounds 
? Other functions 
? Biogenesis 
? Peroxisome assembly 
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
Microbodies 
Institute of Lifelong Learning, University of Delhi 2 
Introduction 
Plant cells, protozoan cells, liver and kidney cells of vertebrates contain structurally simple 
and functionally diverse organelles called Microbodies. They were first reported at 
ultrastructural level in the proximal convoluted tubule of mouse kidney by Rhodin in 1954 
and by Rouiller and Bernhard in 1956 in hepatic parenchymal cells. In plants these 
organelles were first reported by Porter and Caulfield in 1958. Christian Rene
´
 de Duve did 
pioneering work in the discovery and isolation of these subcellular organelles. De Duve 
separated these organelles on the basis of their sedimentation and density properties. The 
1974 Nobel Prize for Physiology and Medicine was awarded to De Duve with Albert Claude 
and George Palade for this work. 
The microbodies are composed of single membrane that surrounds the finely granular 
matrix. These organelles are home to diverse enzymatic reactions including several 
metabolic reactions that provide energy. They can be distinguished from other organelles by 
their richness in enzyme catalase. Their average diameter ranges from 0.1µm to 1.5µm.  
Two types of microbodies have been distinguished : 
? Peroxisomes –the peroxisomes are found in almost all eukaryotic cells and contain 
enzymes that oxidize molecules like fatty acids and amino acids. The byproduct of 
these oxidation reactions is hydrogen peroxide, which is converted to water and 
oxygen by an enzyme catalase present in the peroxisomes. 
? Glyoxysomes – contain in addition to the enzymes found in peroxisomes the 
enzymes isocitrate lyase and/or malate synthetase the two enzymes of the 
glyoxylate cycle. In germinating seeds these organelles are involved in mobilization 
of fats. 
Peroxisomes- Structure 
Peroxisomes are ubiquitous single membrane (typical lipid bilayer) bound organelles that 
contain various metabolic enzymes including those involved in energy metabolism. 
Peroxisomes assume various forms. In rat liver these form large spheres of about 0.5 µm 
diameter with a paracrystalline core while in fibroblasts it consists of small 0.1-0.2 µm 
vesicles. Under some conditions in yeast cells and in liver cells these assume a tubular form, 
which is interconnected to the spherical elements. In 1965, Christian de Duve, while 
studying microbodies of rat liver, showed the presence of oxidases that transfer hydrogen 
Page 4


Microbodies 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
 
 
 
 
Lesson: Microbodies 
Lesson Developer: Geetika Kalra 
College/Department:ANDC, University of Delhi 
  
Microbodies 
Institute of Lifelong Learning, University of Delhi 1 
 
Table of Contents       
 
Chapter: Microbodies                                                        
? Introduction  
? Peroxisomes  
? Structure 
? Functions 
? Fatty acid ß-oxidation 
? Role of peroxisome in photorespiration 
? Conversion of fixed nitrogen to nitrogen-rich 
organic compounds 
? Other functions 
? Biogenesis 
? Peroxisome assembly 
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
Microbodies 
Institute of Lifelong Learning, University of Delhi 2 
Introduction 
Plant cells, protozoan cells, liver and kidney cells of vertebrates contain structurally simple 
and functionally diverse organelles called Microbodies. They were first reported at 
ultrastructural level in the proximal convoluted tubule of mouse kidney by Rhodin in 1954 
and by Rouiller and Bernhard in 1956 in hepatic parenchymal cells. In plants these 
organelles were first reported by Porter and Caulfield in 1958. Christian Rene
´
 de Duve did 
pioneering work in the discovery and isolation of these subcellular organelles. De Duve 
separated these organelles on the basis of their sedimentation and density properties. The 
1974 Nobel Prize for Physiology and Medicine was awarded to De Duve with Albert Claude 
and George Palade for this work. 
The microbodies are composed of single membrane that surrounds the finely granular 
matrix. These organelles are home to diverse enzymatic reactions including several 
metabolic reactions that provide energy. They can be distinguished from other organelles by 
their richness in enzyme catalase. Their average diameter ranges from 0.1µm to 1.5µm.  
Two types of microbodies have been distinguished : 
? Peroxisomes –the peroxisomes are found in almost all eukaryotic cells and contain 
enzymes that oxidize molecules like fatty acids and amino acids. The byproduct of 
these oxidation reactions is hydrogen peroxide, which is converted to water and 
oxygen by an enzyme catalase present in the peroxisomes. 
? Glyoxysomes – contain in addition to the enzymes found in peroxisomes the 
enzymes isocitrate lyase and/or malate synthetase the two enzymes of the 
glyoxylate cycle. In germinating seeds these organelles are involved in mobilization 
of fats. 
Peroxisomes- Structure 
Peroxisomes are ubiquitous single membrane (typical lipid bilayer) bound organelles that 
contain various metabolic enzymes including those involved in energy metabolism. 
Peroxisomes assume various forms. In rat liver these form large spheres of about 0.5 µm 
diameter with a paracrystalline core while in fibroblasts it consists of small 0.1-0.2 µm 
vesicles. Under some conditions in yeast cells and in liver cells these assume a tubular form, 
which is interconnected to the spherical elements. In 1965, Christian de Duve, while 
studying microbodies of rat liver, showed the presence of oxidases that transfer hydrogen 
Microbodies 
Institute of Lifelong Learning, University of Delhi 3 
atom to molecular oxygen forming hydrogen peroxide. He coined the term peroxisomes, for 
the organelle because it produced and consumed hydrogen peroxide. It occurs in some 
animal cells and all photosynthetic cells of higher plants. In plants they perform wide range 
of functions like participation in lipid mobilization, metabolism of free oxygen radicals, 
synthesis of cholesterol and other lipids, catabolism of long chain fatty acids or conversion 
of fixed nitrogen into nitrogen-rich organic compounds and many others. 
Peroxisomes appear circular in cross section, have a single membrane enclosing a granular 
matrix. These organelles do not have their own genome and all their proteins called 
peroxins are encoded by the nuclear genome. These are synthesized on free ribosomes in  
the cytosol and imported into the peroxisomes. Peroxisomes can replicate by division and 
can also be regenerated de novo even if entirely lost from the cell.  
 
Figure:  The core of the peroxisomes appears as crystalline, crystalloid or multilamelllated. 
Source: Duve, C.D. and Baudhun,P. 1966. Physiological reviews 46:303. 
Page 5


Microbodies 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
 
 
 
 
Lesson: Microbodies 
Lesson Developer: Geetika Kalra 
College/Department:ANDC, University of Delhi 
  
Microbodies 
Institute of Lifelong Learning, University of Delhi 1 
 
Table of Contents       
 
Chapter: Microbodies                                                        
? Introduction  
? Peroxisomes  
? Structure 
? Functions 
? Fatty acid ß-oxidation 
? Role of peroxisome in photorespiration 
? Conversion of fixed nitrogen to nitrogen-rich 
organic compounds 
? Other functions 
? Biogenesis 
? Peroxisome assembly 
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Reading 
 
Microbodies 
Institute of Lifelong Learning, University of Delhi 2 
Introduction 
Plant cells, protozoan cells, liver and kidney cells of vertebrates contain structurally simple 
and functionally diverse organelles called Microbodies. They were first reported at 
ultrastructural level in the proximal convoluted tubule of mouse kidney by Rhodin in 1954 
and by Rouiller and Bernhard in 1956 in hepatic parenchymal cells. In plants these 
organelles were first reported by Porter and Caulfield in 1958. Christian Rene
´
 de Duve did 
pioneering work in the discovery and isolation of these subcellular organelles. De Duve 
separated these organelles on the basis of their sedimentation and density properties. The 
1974 Nobel Prize for Physiology and Medicine was awarded to De Duve with Albert Claude 
and George Palade for this work. 
The microbodies are composed of single membrane that surrounds the finely granular 
matrix. These organelles are home to diverse enzymatic reactions including several 
metabolic reactions that provide energy. They can be distinguished from other organelles by 
their richness in enzyme catalase. Their average diameter ranges from 0.1µm to 1.5µm.  
Two types of microbodies have been distinguished : 
? Peroxisomes –the peroxisomes are found in almost all eukaryotic cells and contain 
enzymes that oxidize molecules like fatty acids and amino acids. The byproduct of 
these oxidation reactions is hydrogen peroxide, which is converted to water and 
oxygen by an enzyme catalase present in the peroxisomes. 
? Glyoxysomes – contain in addition to the enzymes found in peroxisomes the 
enzymes isocitrate lyase and/or malate synthetase the two enzymes of the 
glyoxylate cycle. In germinating seeds these organelles are involved in mobilization 
of fats. 
Peroxisomes- Structure 
Peroxisomes are ubiquitous single membrane (typical lipid bilayer) bound organelles that 
contain various metabolic enzymes including those involved in energy metabolism. 
Peroxisomes assume various forms. In rat liver these form large spheres of about 0.5 µm 
diameter with a paracrystalline core while in fibroblasts it consists of small 0.1-0.2 µm 
vesicles. Under some conditions in yeast cells and in liver cells these assume a tubular form, 
which is interconnected to the spherical elements. In 1965, Christian de Duve, while 
studying microbodies of rat liver, showed the presence of oxidases that transfer hydrogen 
Microbodies 
Institute of Lifelong Learning, University of Delhi 3 
atom to molecular oxygen forming hydrogen peroxide. He coined the term peroxisomes, for 
the organelle because it produced and consumed hydrogen peroxide. It occurs in some 
animal cells and all photosynthetic cells of higher plants. In plants they perform wide range 
of functions like participation in lipid mobilization, metabolism of free oxygen radicals, 
synthesis of cholesterol and other lipids, catabolism of long chain fatty acids or conversion 
of fixed nitrogen into nitrogen-rich organic compounds and many others. 
Peroxisomes appear circular in cross section, have a single membrane enclosing a granular 
matrix. These organelles do not have their own genome and all their proteins called 
peroxins are encoded by the nuclear genome. These are synthesized on free ribosomes in  
the cytosol and imported into the peroxisomes. Peroxisomes can replicate by division and 
can also be regenerated de novo even if entirely lost from the cell.  
 
Figure:  The core of the peroxisomes appears as crystalline, crystalloid or multilamelllated. 
Source: Duve, C.D. and Baudhun,P. 1966. Physiological reviews 46:303. 
Microbodies 
Institute of Lifelong Learning, University of Delhi 4 
 
Figure: Structure of peroxisomes 
Source:http://upload.wikimedia.org/wikipedia/commons/thumb/c/cb/Peroxisome.svg/300px
-Peroxisome.svg.png 
DID YOU KNOW? 
? Transport of proteins into peroxisomes is facilitated by a specific sequence of three 
amino acids located at the carboxyl terminus of these proteins. 
? Interestingly, if this sequence of amino acids is attached to a cytosolic protein, the 
protein gets transported into peroxisomes.  
? If this sequence is lacking in a human being – a disease called Zellweger syndrome 
occurs which leads to severe protein deficiency in peroxisomes. Such patients suffer 
from severe abnormalities in brain, liver and kidney and die soon after birth. 
 
 
Functions 
Peroxisomes contain 50 different enzymes involved in a variety of biochemical pathways. 
Although initially identified in organelles that carried out oxidation reactions leading to the  
production and eventually destruction of hydrogen peroxide. Peroxisomes contain the 
enzymes – oxidases and catalases. The oxidases oxidizes the substrates ( RH
2
) and reduces 
oxygen to hydrogen peroxide (H
2
O
2 
). The hydrogen peroxide is decomposed by catalase 
either by conversion to water (I) or by oxidation of another organic compound - R’H
2 
(II).