🧈 Plant Fatty Acids and Lipids
Study major, minor, unusual, and essential fatty acids along with simple and compound lipids.
Lipids are one of the major biochemical groups in plants, and fatty acids form their most important building blocks. Understanding fatty acids helps explain plant oil composition, membrane structure, storage function, and nutritional significance.
What Are Fatty Acids?
Fatty acids are carboxylic acids with hydrocarbon chains, usually containing from 2 to 36 carbon atoms.
More than 200 fatty acids have been reported from plants, but only a smaller number occur widely and in large quantities.
Fatty acids may be:
- major fatty acids
- minor fatty acids
- unusual fatty acids
They form essential parts of fats, oils, membranes, and signaling molecules.
Major Fatty Acids
The major plant fatty acids are generally straight-chain saturated or unsaturated fatty acids.
Saturated major fatty acids
- lauric acid
- myristic acid
- palmitic acid
- stearic acid
Unsaturated major fatty acids
- oleic acid
- linoleic acid
- linolenic acid
These occur widely in plant lipids.
Fatty acids are commonly written using a shorthand notation such as 18:2, where:
- the first number = number of carbon atoms
- the second number = number of double bonds
If the position of double bonds is needed, it is shown separately.
Naturally occurring unsaturated fatty acids usually have their double bonds in the cis configuration.
Minor Fatty Acids
Minor fatty acids occur in smaller amounts than the major ones.
Examples include:
- butyric acid
- caproic acid
- caprylic acid
- capric acid
Although they are less abundant, they are still biochemically important and help explain variation in lipid composition across organisms and tissues.
Unusual Fatty Acids
Unusual fatty acids are found only in certain species, genera, or families.
Examples from the lesson include:
- ricinoleic acid in castor bean
- erucic acid in rapeseed
- hydnocarpic and chaulmoogric acids in chaulmoogra oil
These unusual fatty acids are important because they often have specialized industrial or biological significance.
Essential Fatty Acids
Essential fatty acids are those that the human body cannot synthesize in sufficient quantity and must therefore obtain from the diet.
Important essential fatty acids include:
- linoleic acid
- linolenic acid
The lesson also notes the importance of:
- arachidonic acid
Linoleic acid belongs to the n-6 family, while linolenic acid belongs to the n-3 family.
These fatty acids are important because they contribute to:
- membrane composition
- growth and maintenance
- formation of eicosanoids
Eicosanoids
Arachidonic acid acts as a precursor for:
- prostaglandins
- thromboxanes
- prostacyclins
These compounds are important regulatory molecules in animal systems.
Simple Lipids
Simple lipids contain only fatty acids and an alcohol such as glycerol or a long-chain alcohol.
They include:
- fats
- oils
- waxes
Fats and oils
The simplest and most common lipids are triacylglycerols, also called triglycerides.
They consist of:
- glycerol
- three fatty acids esterified to glycerol
If all three fatty acids are the same, the triacylglycerol is simple. If they differ, it is a mixed triacylglycerol.
In general:
- fats are solid at room temperature
- oils are liquid at room temperature
Plant lipids are commonly stored as oils in seeds and sometimes in fruit tissues.
Waxes
Waxes are esters of long-chain fatty acids with long-chain alcohols.
They are important for:
- surface protection
- water loss reduction
- industrial use
Examples include:
- lanolin
- beeswax
- carnauba wax
- jojoba oil as a liquid wax
Cuticular wax on plant surfaces helps reduce water loss and protects against injury and attack.
Compound Lipids
Compound lipids contain additional groups besides fatty acids and alcohol.
They include:
- glycerophospholipids
- sphingophospholipids
- glycolipids
- sulpholipids
- lipoproteins
These lipids are especially important in membranes.
Glycerophospholipids
These contain:
- glycerol
- fatty acids
- phosphoric acid
- usually a nitrogenous base or other alcohol residue
Examples include:
- phosphatidyl choline (lecithin)
- phosphatidyl ethanolamine (cephalin)
- phosphatidyl serine
- phosphatidyl inositol
- phosphatidyl glycerol
Sphingophospholipids
In these lipids, the backbone alcohol is sphingosine rather than glycerol. They are structurally important in membranes and differ in linkage type from glycerophospholipids.
Glycolipids and sulpholipids
These are characterized by carbohydrate or sulphate-containing groups and also contribute to membrane structure and function.
Agricultural and Biological Importance
Plant fatty acids and lipids are important because they:
- store energy
- build membranes
- influence seed quality
- affect nutritional value of oils
- contribute to industrial raw materials
Example: oilseed crops are valued largely because of the type and proportion of fatty acids they store.
Summary Cheat Sheet
- Fatty acids are carboxylic acids with hydrocarbon chains.
- They may be major, minor, unusual, or essential.
- Important major unsaturated fatty acids: oleic, linoleic, linolenic.
- Essential fatty acids include linoleic and linolenic acids.
- Triacylglycerols are the main storage lipids in plants.
- Waxes protect surfaces and reduce water loss.
- Compound lipids such as phospholipids are major membrane components.
- Fatty acid composition is important for plant physiology, nutrition, and industrial use.
References
1 source • [1]
References
Biochemistry references used for lesson preparation.
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