1. Cellular Biochemistry and metabolism 1 Lecturer of Biochemistry
Digestion of lipids
Cellular Biochemistry and metabolism 1
CLS 331
Dr. Samah Kotb
Lecturer of Biochemistry
2015

2. Dr Samah Kotb

3. Dr Samah Kotb

4. Definition
Lipids are complex molecules composed of carbon , hydrogen , and oxygen.
Lipids are insoluble in water and soluble in nonpolar solvents.
Most lipids are non-polar and are hydrophobic because they contain hydrocarbon chains.

5. Functions of lipids The Functions of Fat in the Body: Energy source.
Serves as an energy reserve.
Structural component of cell membrane. Cell Membrane

6. 4. Thermal Insulator :
Subcutaneous layer of fat reduces heat loss in cold weather (helps maintain body temperature).

7. CLASSIFICATIONS OF FATTY ACID
Length of the Carbon Chain
Long-chain, medium-chain, short-chain
Degree of Unsaturation
Saturated, Unsaturated (Mono, Poly)
Location of Double Bonds
Omega-3 Fatty Acid, Omega-6 Fatty Acid

8. 1) Saturated fatty acids
Dr Samah Kotb

9. Properties of saturated fatty acids
General Formula: CH3 (CH2)n COOH.
Each C being “saturated” with H.
Contain only single C–C bonds.
long, straight chain.

10. Properties of saturated fatty acids
Closely packed.
Strong attractions between chains.
High melting points.
Solids at room temperature.

11. Examples of Saturated fatty acids
Dr Samah Kotb

12. LAURIC ACID

14. 2) unsaturated fatty acids
Dr Samah Kotb

15. Properties of unsaturated fatty acids
Contain one or more double C=C bonds.
The links made by double bonded C
prevent the molecules from packing
tightly together.
Few interactions between chains.

16. Classification of lipids 3.Precursor & Derived Lipids
1. Simple Lipids
2. Complex
Lipids
3.Precursor & Derived Lipids

17. Simple lipids
Esters of fatty acids and alcohol. (trihydric or monohydric alcohol).

18. Triglycerides Triglycerides are the main dietary fats in human body.
It is a naturally occurring ester of three fatty acids and glycerol that is the chief constituent of fats and oils.
Glycerol forms the “backbone” of the fat.

20. FAT vs. OIL Fat: Oil: is solid at room temperature.
is prevalent in meats, whole milk, butter, and cheese.
Oil:
Contain high proportion of unsaturated fatty acids and saturated fatty acids.
is liquid at room temperature.
is prevalent in plants such as olive and safflower.
corn oil contains 86% unsaturated fatty acids and 14% saturated fatty acids

21. Complex lipids
Esters of fatty acids with various alcohols along with an additional group.
Simple lipid + Additional group = Complex Lipids
a. Phospholipids: Glycerophospholipids , Sphingophospholipids.
b. Glycolipids
c. Other Complex Lipids: Lipoproteins ,aminolipids and
sulfolipids.

22. Digestion OF
LIPIDS
Dr Samah Kotb

23. Dr Samah Kotb

24. Digestion & Absorption of lipids
The major lipids in the diet are triacylglycerols.
Hydrolysis of triacylglycerols is initiated by gastric lipases that attack the ester bond, forming 1,2-diacylglycerols and free fatty acids, aiding emulsification.
Dr Samah Kotb

25. Digestion & Absorption of lipids
Pancreatic lipase is secreted into the small intestine and requires a further pancreatic protein, colipase, for activity.
It is specific for the primary ester links in triacylglycerols resulting in 2-monoacylglycerols and free fatty acids as the major end-products of luminal triacylglycerol digestion.
Dr Samah Kotb

26. Triacylglycerols 1,2-diacylglycerols + free fatty acids
Stomach
gastric lipases
1,2-diacylglycerols + free fatty acids
Pancreatic lipase
small intestine
2-monoacylglycerols + free fatty acids
hydrolysis
Secreted as chylomicrons into the lymphatics, entering the blood stream via the thoracic duct .
free fatty acids +
glycerol
Portal vein
Dr Samah Kotb

27. Digestion & Absorption of lipids
Monoacylglycerols are hydrolyzed with difficulty to glycerol and free fatty acids.
Bile salts, formed in the liver and secreted in the bile, enable emulsification of the products of lipid digestion into micelles and liposomes together with phospholipids and cholesterol from the bile.
Dr Samah Kotb

28. Digestion & Absorption of lipids
Because the micelles are soluble, they allow the products of digestion, including the fat soluble vitamins, to be transported through the aqueous environment of the intestinal lumen and permit close contact with the brush border of the mucosal cells, allowing uptake into the epithelium, mainly of the jejunum.
Dr Samah Kotb

29. Dr Samah Kotb

30. Digestion & Absorption of lipids
The bile salts pass on to the ileum, where most are absorbed into the enterohepatic circulation.
Within the intestinal epithelium, 1-monoacylglycerols are hydrolyzed to fatty acids and glycerol and 2-monoacylglycerols are re-acylated to triacylglycerols via the monoacylglycerol pathway.
Dr Samah Kotb

31. Digestion & Absorption of lipids
Glycerol released in the intestinal lumen is not reutilized but passes into the portal vein; glycerol released within the epithelium is reutilized for triacylglycerol synthesis via the normal phosphatidic acid pathway.
Dr Samah Kotb

32. Digestion & Absorption of lipids
All long-chain fatty acids absorbed are converted to triacylglycerol in the mucosal cells and, together with the other products of lipid digestion, secreted as chylomicrons into the lymphatics, entering the blood stream via the thoracic duct .
Dr Samah Kotb

33. Dr Samah Kotb