Lecture 11 - Lipid metabolism | Plant Metabolism - Botany PDF Download

 Page 1


Lipid Metabolism 
 
Institute of Lifelong Learning, University of Delhi                                                                            
 
0 
 
 
 
 
 
 
Discipline: Botany 
Paper: Plant Metabolism 
Lesson: Lipid Metabolism 
Lesson Developer: Dr. Misha Yadav  
Department/College: Department of Botany, Shivaji 
College 
University of Delhi 
 
 
 
 
 
 
 
Page 2


Lipid Metabolism 
 
Institute of Lifelong Learning, University of Delhi                                                                            
 
0 
 
 
 
 
 
 
Discipline: Botany 
Paper: Plant Metabolism 
Lesson: Lipid Metabolism 
Lesson Developer: Dr. Misha Yadav  
Department/College: Department of Botany, Shivaji 
College 
University of Delhi 
 
 
 
 
 
 
 
Lipid Metabolism 
 
Institute of Lifelong Learning, University of Delhi                                                                            
 
1 
 
Table of Contents 
Chapter: Lipid Metabolism 
? Introduction  
? Lipid synthesis 
? Fatty acid biosynthesis 
? Synthesis of triglycerides: lipid deposition in 
seeds 
? Synthesis of oil bodies 
? Oil bodies: structure and composition 
? Catabolism of Triglycerides 
? Lipolysis: Mobilization of oil bodies 
? Fatty acid oxidation/ Beta (ß) oxidation 
? Alpha (a) oxidation 
? Glyoxylate cycle 
? Gluconeogenesis 
? Summary 
? Exercise/ Practice 
? Glossary 
? References 
? Weblinks 
 
 
 
 
 
Page 3


Lipid Metabolism 
 
Institute of Lifelong Learning, University of Delhi                                                                            
 
0 
 
 
 
 
 
 
Discipline: Botany 
Paper: Plant Metabolism 
Lesson: Lipid Metabolism 
Lesson Developer: Dr. Misha Yadav  
Department/College: Department of Botany, Shivaji 
College 
University of Delhi 
 
 
 
 
 
 
 
Lipid Metabolism 
 
Institute of Lifelong Learning, University of Delhi                                                                            
 
1 
 
Table of Contents 
Chapter: Lipid Metabolism 
? Introduction  
? Lipid synthesis 
? Fatty acid biosynthesis 
? Synthesis of triglycerides: lipid deposition in 
seeds 
? Synthesis of oil bodies 
? Oil bodies: structure and composition 
? Catabolism of Triglycerides 
? Lipolysis: Mobilization of oil bodies 
? Fatty acid oxidation/ Beta (ß) oxidation 
? Alpha (a) oxidation 
? Glyoxylate cycle 
? Gluconeogenesis 
? Summary 
? Exercise/ Practice 
? Glossary 
? References 
? Weblinks 
 
 
 
 
 
Lipid Metabolism 
 
Institute of Lifelong Learning, University of Delhi                                                                            
 
2 
Learning Outcomes 
In this chapter you will learn about: 
? The synthesis of lipids, triglycerides and oil body formation 
? The catabolism of fatty acids 
? The various pathways of catabolism : (ß) oxidation, (a) oxidation and glyoxalate 
cycle 
? The pathway of gluconeogensis 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Page 4


Lipid Metabolism 
 
Institute of Lifelong Learning, University of Delhi                                                                            
 
0 
 
 
 
 
 
 
Discipline: Botany 
Paper: Plant Metabolism 
Lesson: Lipid Metabolism 
Lesson Developer: Dr. Misha Yadav  
Department/College: Department of Botany, Shivaji 
College 
University of Delhi 
 
 
 
 
 
 
 
Lipid Metabolism 
 
Institute of Lifelong Learning, University of Delhi                                                                            
 
1 
 
Table of Contents 
Chapter: Lipid Metabolism 
? Introduction  
? Lipid synthesis 
? Fatty acid biosynthesis 
? Synthesis of triglycerides: lipid deposition in 
seeds 
? Synthesis of oil bodies 
? Oil bodies: structure and composition 
? Catabolism of Triglycerides 
? Lipolysis: Mobilization of oil bodies 
? Fatty acid oxidation/ Beta (ß) oxidation 
? Alpha (a) oxidation 
? Glyoxylate cycle 
? Gluconeogenesis 
? Summary 
? Exercise/ Practice 
? Glossary 
? References 
? Weblinks 
 
 
 
 
 
Lipid Metabolism 
 
Institute of Lifelong Learning, University of Delhi                                                                            
 
2 
Learning Outcomes 
In this chapter you will learn about: 
? The synthesis of lipids, triglycerides and oil body formation 
? The catabolism of fatty acids 
? The various pathways of catabolism : (ß) oxidation, (a) oxidation and glyoxalate 
cycle 
? The pathway of gluconeogensis 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Lipid Metabolism 
 
Institute of Lifelong Learning, University of Delhi                                                                            
 
3 
Introduction 
Lipids are amongst the variety of biomolecules vital for the existence of cellular organisms. 
Lipids are a heterogeneous group of molecules sparingly soluble in water but highly soluble 
in non-polar organic solvents. Most of world’s lipids are produced by plants. Other 
organisms including human beings depend on the lipids synthesized by plants to fulfill lipid 
requirements.  A few of the important roles played by them are listed as follows: 
? They serve as means of energy storage in concentrated form especially in the form 
of triglycerides (TGs). 
? They are important components of cell membranes. 
? They are important for absorption of fat soluble vitamins (A, D, E and K) in animals. 
? Certain hormones are derived from lipids. Secondary metabolites derived from lipids 
have regulatory roles. Examples are prostaglandins and oxyilipins. 
? They serve to protect animal and plant surfaces from desiccation and infections, in 
the form of oils and waxy coverings.  
 
Lipids include fats, oils, waxes and compounds with similar properties. Common types are 
fatty acids, neutral lipids, phospholipids, glycerolipids, terpenes and steroids. Fatty acids are 
composed of long hydrocarbon chains terminating in carboxyl groups. Fatty acids can be 
categorized into two types: saturated and unsaturated fatty acids. Unsaturated fatty acid 
has at least one double bond in their hydrocarbon chain. Tremendous fatty acid diversity 
exists in lipids. To date, nearly 300 naturally occurring fatty acids have been described. 
Some commonly present fatty acids are shown in the table. 
Table: Some common fatty acids present in lipids. 
Name of fatty 
acid 
Number of 
carbon atoms: 
double bonds 
Structure 
Lauric acid  12:0 CH
3
(CH
2
)
10
COOH 
Myristic acid  14:0 CH
3
(CH
2
)
12
COOH 
Palmitic acid  16:0 CH
3
(CH
2
)
14
COOH 
Stearic acid  18:0 CH
3
(CH
2
)
16
COOH 
Oleic acid  18:1 CH
3
(CH
2
)
7
CH=CH(CH
2
)
7
COOH 
Linoleic acid  18:2 CH
3
(CH
2
)
4
CH=CHCH
2
CH=CH(CH
2
)
7
COOH 
Page 5


Lipid Metabolism 
 
Institute of Lifelong Learning, University of Delhi                                                                            
 
0 
 
 
 
 
 
 
Discipline: Botany 
Paper: Plant Metabolism 
Lesson: Lipid Metabolism 
Lesson Developer: Dr. Misha Yadav  
Department/College: Department of Botany, Shivaji 
College 
University of Delhi 
 
 
 
 
 
 
 
Lipid Metabolism 
 
Institute of Lifelong Learning, University of Delhi                                                                            
 
1 
 
Table of Contents 
Chapter: Lipid Metabolism 
? Introduction  
? Lipid synthesis 
? Fatty acid biosynthesis 
? Synthesis of triglycerides: lipid deposition in 
seeds 
? Synthesis of oil bodies 
? Oil bodies: structure and composition 
? Catabolism of Triglycerides 
? Lipolysis: Mobilization of oil bodies 
? Fatty acid oxidation/ Beta (ß) oxidation 
? Alpha (a) oxidation 
? Glyoxylate cycle 
? Gluconeogenesis 
? Summary 
? Exercise/ Practice 
? Glossary 
? References 
? Weblinks 
 
 
 
 
 
Lipid Metabolism 
 
Institute of Lifelong Learning, University of Delhi                                                                            
 
2 
Learning Outcomes 
In this chapter you will learn about: 
? The synthesis of lipids, triglycerides and oil body formation 
? The catabolism of fatty acids 
? The various pathways of catabolism : (ß) oxidation, (a) oxidation and glyoxalate 
cycle 
? The pathway of gluconeogensis 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Lipid Metabolism 
 
Institute of Lifelong Learning, University of Delhi                                                                            
 
3 
Introduction 
Lipids are amongst the variety of biomolecules vital for the existence of cellular organisms. 
Lipids are a heterogeneous group of molecules sparingly soluble in water but highly soluble 
in non-polar organic solvents. Most of world’s lipids are produced by plants. Other 
organisms including human beings depend on the lipids synthesized by plants to fulfill lipid 
requirements.  A few of the important roles played by them are listed as follows: 
? They serve as means of energy storage in concentrated form especially in the form 
of triglycerides (TGs). 
? They are important components of cell membranes. 
? They are important for absorption of fat soluble vitamins (A, D, E and K) in animals. 
? Certain hormones are derived from lipids. Secondary metabolites derived from lipids 
have regulatory roles. Examples are prostaglandins and oxyilipins. 
? They serve to protect animal and plant surfaces from desiccation and infections, in 
the form of oils and waxy coverings.  
 
Lipids include fats, oils, waxes and compounds with similar properties. Common types are 
fatty acids, neutral lipids, phospholipids, glycerolipids, terpenes and steroids. Fatty acids are 
composed of long hydrocarbon chains terminating in carboxyl groups. Fatty acids can be 
categorized into two types: saturated and unsaturated fatty acids. Unsaturated fatty acid 
has at least one double bond in their hydrocarbon chain. Tremendous fatty acid diversity 
exists in lipids. To date, nearly 300 naturally occurring fatty acids have been described. 
Some commonly present fatty acids are shown in the table. 
Table: Some common fatty acids present in lipids. 
Name of fatty 
acid 
Number of 
carbon atoms: 
double bonds 
Structure 
Lauric acid  12:0 CH
3
(CH
2
)
10
COOH 
Myristic acid  14:0 CH
3
(CH
2
)
12
COOH 
Palmitic acid  16:0 CH
3
(CH
2
)
14
COOH 
Stearic acid  18:0 CH
3
(CH
2
)
16
COOH 
Oleic acid  18:1 CH
3
(CH
2
)
7
CH=CH(CH
2
)
7
COOH 
Linoleic acid  18:2 CH
3
(CH
2
)
4
CH=CHCH
2
CH=CH(CH
2
)
7
COOH 
Lipid Metabolism 
 
Institute of Lifelong Learning, University of Delhi                                                                            
 
4 
Linolenic acid  18:3 CH
3
CH
2
CH=CHCH
2
CH=CHCH
2
CH=CH(CH
2
)
7
COOH 
 
The percentage of fatty acids present in plant lipids varies according to the species. Fatty 
acids are essential components of triglycerides/ triacylglycerols. TAGs consist of three fatty 
acid molecules esterified to a glycerol backbone.  Their biosynthesis, storage and 
degradation will be discussed shortly. 
They are non-polar.  They serve as major form of storage lipids. Upon complete oxidation 
TAGs release more than double the energy released during carbohydrate or protein 
hydrolysis. Thus, they are considered efficient reserves which accumulate fatty acids, for 
energy production and serve as a source of carbon blocks for synthesis of membranes. In 
higher plants, TAG deposition is mostly associated with seed tissue in the form of lipid 
droplets. These TAG deposits occur in the form of intracellular organelles known as oil 
bodies.  
 
Figure: Structure of unsaturated fat triglyceride 
Source: 
http://upload.wikimedia.org/wikipedia/commons/b/be/Fat_triglyceride_shorthand_formula.P
NG (cc) 
The mechanism of synthesis and degradation of TAG has been well characterized in 
developing seeds and during seed germination respectively. In plants the de novo synthesis 
of fatty acids occurs in plastids. Such fatty acids are then exported to endoplasmic 
reticulum, to be assembled into TAGs. The mechanism involved for membrane glycerolipid 
synthesis is similar to that for TAG synthesis. The flux of fatty acids from plastids, cytosolic 
acyl-CoA pool, specificity of enzymes (such as acyltransferases) involved in the pathway