Triglycerides
Laura Armstrong
Teacher
Contents
Recall Questions
This topic requires prior knowledge of lipids. You can test your knowledge on these below.
What are the two main groups of lipids? (1 mark)
Triglycerides and phospholipids.
What reaction joins glycerol and fatty acids to form a triglyceride? (1 mark)
A condensation reaction, forming ester bonds (and water)
What is the difference between saturated and unsaturated fatty acids? (1 mark)
Saturated fatty acids contain only single bonds between carbon atoms, while unsaturated fatty acids have one or more double bonds between carbon atoms.
Topic Explainer Video
Check out this @LauraDoesBiology video that explains triglycerides or read the full notes below. Once you've gone through the whole note, try out the practice questions!
Structure of Triglycerides
- Triglycerides are a type of lipid made up of:
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One molecule of glycerol (a three-carbon alcohol).
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Three fatty acids attached to glycerol via ester bonds.
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Fatty acids have a chain of -CH₂- known as a hydrocarbon chain. The number of carbons varies and can be represented as -R. These fatty acids can be either saturated or unsaturated.
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- The formation of a triglyceride involves condensation reactions, releasing three molecules of water.
- The breakdown of triglycerides occurs through hydrolysis, requiring water to break the ester bonds.
Saturated vs. Unsaturated Fatty Acids
- Saturated fatty acids:
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Only single bonds between carbon atoms in the hydrocarbon chain.
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Found in animal fats (e.g., butter, lard).
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Solid at room temperature due to closely packed molecules.
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- Unsaturated fatty acids:
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Contain one (monounsaturated) or multiple (polyunsaturated) double C=C bonds the hydrocarbon chain.
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Found in plant oils (e.g., olive oil, sunflower oil).
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Liquid at room temperature because double bonds create kinks, preventing tight packing between the phospholipids..
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Functions and Uses of Triglycerides
- Energy Storage:
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Triglycerides have a high ratio of carbon-hydrogen bonds, making them excellent energy stores.
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They provide more energy per gram than carbohydrates.
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- Waterproofing:
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They are insoluble in water (hydrophobic) so do not affect water potential and do not affect osmosis in cells.
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Used for waterproofing in waxy cuticles of plants and insect exoskeletons.
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- Insulation:
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Act as thermal insulators in mammals (e.g., blubber in whales).
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Provide electrical insulation around nerve cells.
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- Protection:
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Stored around vital organs to provide mechanical protection (e.g., kidneys).
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- Buoyancy:
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Triglycerides are less dense than water, helping aquatic animals such as seals and whales to stay afloat.
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Key Terms
- Triglyceride: A lipid made of one glycerol molecule and three fatty acids.
- Ester bond: The bond formed between glycerol and fatty acids in a condensation reaction.
- Saturated fatty acid: A fatty acid with only single bonds between carbon atoms.
- Unsaturated fatty acid: A fatty acid containing at least one double bond between carbon atoms.
- Hydrophobic: Water-repelling; does not dissolve in water.
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Exam Tip
When explaining the function of triglycerides, always link structure to function.
- Example: "Triglycerides are insoluble, so they do not affect osmosis in cells, making them effective energy stores."
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Explain how a triglyceride is formed from its component parts. (4 marks)
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Made from glycerol and three fatty acids.
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Joined together via condensation reactions.
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Forming three ester bonds.
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Removing three molecules of water.