1. CH 8: Lipids

2. Lipids Defined
A lipid is an organic compound found in living organisms that is:
insoluble (or only sparingly soluble) in water
soluble in non-polar organic solvents.
Lipids do not have common functional groups that serves as the basis for defining such compounds.

3. Functions of Lipids Source of energy – 9kcal/gram
Provide thermal insulation and pad organs
Component of all cells – in membranes
Some act as hormones – steroid hormones
Protective coating - waxes

4. Types of Lipids
Energy-storage lipids –triacylglycerols, triglycerols, “fats”
Membrane lipids - phospholipids, sphingo(glyco)lipids, and cholesterol
Emulsification lipids - bile acids
Chemical messenger lipids - steroid hormones and eicosanoids
Protective-coating lipids - biological waxes

6. Fatty Acids (FA)
Fatty acids are naturally occurring unbranched monocarboxylic acids
Biological FA have an even # of carbon atoms:
Short-chain fatty acids: C4 - C5-6
Medium chain fatty acids: C6-8 - C10
Long chain fatty acids: C12 - C26

7. Types of Fatty Acids Saturated (SFA) Unsaturated Fatty Acids
Fatty acid with only C to C single bonds
Unsaturated Fatty Acids
Monounsaturated (MUFA) - FA with one C to C double bond present
Polyunsaturated (PUFA) - FA with 2 or more C to C double bonds present
Double bonds are in the cis form

8. Fatty Acids

9. Mono-unsaturated Fatty Acidsw D

10. Describing Fatty Acids
Identify omega & delta “end” of the fatty acid
State number of carbons: # double bonds
Give location of double bonds, counting from the delta “end”

12. Properties Fatty Acids
Water solubility decreases as C# increases
Short chain FA are fairly water soluble
Medium and long chain FA are water insoluble
As the number of carbons increases so does the melting point
For a given number of carbons, mp increases as the # of cis double bonds increases
Trans double bonds do not impact mp significantly
UC Davis Wiki

13. Triglyceride = glycerol + 3 fatty acids aka - triglycerols

14. TG Formation – 3 ester linkages
Triglyceride

15. Properties of TG
The nature of the fatty acids bonded to the glycerol backbone determines the properties of the TG
Fats – solid TG
Primarily saturated fatty acids
Primarily animal sources
Oils – liquid TG
Many unsaturated fatty acids
Good sources - plant and fish oils

16. Sources of FA Saturated FA MUFA PUFA Animals fats
Butter, lard, lamb, beef….
Coconut “oil”
MUFA
Olive oil
Canola oil
PUFA
Vegetable oils, corn oil,

18. Reactions of TG Hydrolysis Saponification – 2 step process
+ 3 H2O  glycerol FA (or a monoglyceride and 2 FA)
Reaction requires heat and acidic conditions OR digestive enzymes
Saponification – 2 step process
Step one, hydrolyze the TG to 3 FA + glycerol
Step two, react the FA with 3 NaOH or 3 KOH  3 soaps

19. 3. Hydrogenation reaction -- add H2 to the double bonds -- complete hydrogenation converts all double bonds to single bonds (fully hydrogenated) --reaction saturates the oil --partial hydrogenation occurs when some of the double bonds are hydrogenated --remaining double bonds are often converted in to trans form

20. Oxidation of unsaturated FA –> rancid oil
…CH=CH…. (O) 2 aldehydes (O)  2 carboxylic acids

21. Essential Fatty Acids
Fatty acids that must be obtained from dietary sources – are not synthesized within the body
Two most important essential fatty acids are:
Linoleic acid (18:2) - omega 6
Linolenic acid (18:3) - omega 3
Both are needed for:
Proper membrane structure
Serve as starting materials for the production of several nutritionally important longer-chain omega-6 and omega-3 fatty acids

22. Current recommended amounts are: total fat intake in calories:
15% - Monounsaturated fat
10% - Polyunsaturated
<10% - Saturated fats
Studies also indicate that:
Monounsaturated fats are considered “good fats”
Saturated fats are considered “bad fats”
Trans-monounsaturated fats are considered “bad fats”
Polyunsaturated fats can be both “good fats” and “bad fats”
Omega 3 and 6 are important “good fats”

23. Membrane Lipids Phospholipids Sphingoglycolipids Cholesterol (steroid)
Glycerophospholipids
Sphingophospholipids
Sphingoglycolipids
Cholesterol (steroid)
See page 314

24. Phospholipids aka - glycerophospolipid

25. Sphingophospholipid See page 313 and 314 Sphinogosine backbone with
Fatty acid bonded to sphingosine by an amide bond
Phosphate bonded to an amino alcohol

26. Relate this structure to that on page 313

27. Sphingoglycolipids

28. Cholesterol – found in the membranes of animal cells
General steroid structure

29. Steroids – Functions Vary
Membrane lipids
Cholesterol – animal cell membranes
Messenger lipids
Hormones – testosterone, estrogen, see pages 322/23
Emulsification lipids
Bile salts

30. Messenger Lipids - Eicosanoids
Eicosanoids are Arachidonic acid (20:4) derivatives:
Have profound physiological effects at extremely low concentrations.
Eicosanoids are hormone-like molecules
Exert their effects in the tissues where they are synthesized.
Eicosanoids usually have a very short “life.”
Physiological effects of eicosanoids:
Inflammatory response
Production of pain and fever
Regulation of blood pressure
Induction of blood clotting
Control of reproductive functions, such as induction of labor
Regulation of the sleep/wake cycle

31. Eicosanoids Arachidonic acid (20:4) derivatives