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
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