Digestion of lipids
Laura Armstrong
Teacher
Contents
Recall Questions
This topic requires prior knowledge of enzyme action and the chemical structure of lipids. You can test your knowledge on these below.
Describe the structure of a triglyceride.
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A triglyceride consists of one glycerol molecule and three fatty acids.
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Joined together by three ester bonds (made in condensation reactions)
Explain the role of bile salts in lipid digestion.
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Bile salts emulsify lipids by breaking large droplets into smaller ones.
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This increases the surface area for lipase action.
What are the products of lipid digestion?
Monoglycerides and fatty acids.
Topic Explainer Video
Digestion of Lipids
- Lipids, mainly triglycerides, are broken down by enzymes into smaller molecules for absorption.
- This process occurs in the small intestine, where bile salts and lipases play a key role.
Role of Bile Salts
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Produced by the liver and stored in the gallbladder.
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Released from the gall bladder, via the bile duct, into the small intestine.
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Emulsify lipids, breaking large fat globules into smaller droplets.
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Increases surface area for lipase enzymes to act more efficiently.
Action of Lipase and Formation of Micelles
Action of Lipase
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Pancreatic lipase hydrolyses triglycerides into monoglycerides and free fatty acids.
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A monoglyceride is a molecule of glycerol with one fatty acid attached.
Formation of Micelles
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After digestion, monoglycerides and fatty acids remain associated with bile salts forming what we call micelles.
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Micelles transport the monoglycerides and fatty acids to the epithelial cells of the ileum.
- At the membrane, monoglycerides and fatty acids diffuse into the epithelial cells as micelles disassemble.
Key Terms
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Bile salts: Molecules that emulsify lipids, increasing their surface area for lipase action and digestion.
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Emulsification: Breakdown of large lipid droplets into smaller ones for easier enzyme action.
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Lipase: Enzyme that catalyses the hydrolysis of triglycerides into monoglycerides and fatty acids.
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Micelles: Small transport structures composed of bile salts, fatty acids, and monoglycerides.
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Exam Tip
Common Mistake: Students often forget that bile salts do NOT digest lipids—they only emulsify them. They are not enzymes. Lipase is the enzyme responsible for lipid hydrolysis.
No answer provided.
Describe how lipids are digested. (4 marks)
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Bile salts emulsify lipids into smaller droplets.
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This increases the surface area for increased lipase action.
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Lipase hydrolyses ester bonds in triglycerides.
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Producing monoglycerides and free fatty acids.
Practice Question 1
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!
Practice Question 2
If you want to try out another one, check this video out and see how you do!