1. The Organic Chemistry of Lipids
Chapter 27
The Organic Chemistry of Lipids
Organic Chemistry
6th Edition
Paula Yurkanis Bruice

2. Lipids are soluble in nonpolar organic compounds and have a variety of structures and functions:

3. Common Naturally Occurring Fatty Acids

4. Fatty acids, a major group of lipids, are carboxylic
acids with long hydrocarbon chains.
Polyunsaturated fatty acids have more than one double bond.
The double bonds in naturally occurring fatty acids have the cis configuration.
Double bonds in naturally occurring unsaturated fatty acids are separated by one methylene group.

5. Unsaturated fatty acids have lower melting points than

6. Waxes Are High-Molecular-Weight Esters

7. Fats and Oils
The three OH groups of glycerol are esterified with fatty acids.
A simple triacylglycerol has three identical fatty acid components.
A mixed triacylglycerol has two or three different fatty acid components.

8. Fats are triacylglycerols existing as solid or semisolid
state at room temperature:

9. Oils are liquid triacylglycerols:

10. Some or all of the double bonds of polyunsaturated oils
can be reduced by catalytic hydrogenation (Section 4.12)
Catalytic hydrogenation is used to convert oils to fats (e.g., vegetable oil to margarine).
This process also isomerizes double bonds from cis to trans, resulting in unhealthy trans fats.

11. Oxidation of Polyunsaturated
Fats and Oils by O2

12. Phosphoacylglycerols
They are the major components of cell membranes.
The terminal OH group of glycerol is esterified with
phosphoric acid.

13. The most common phosphoacylglycerols in membranes are phosphodiesters.
The alcohols most commonly used to form the second ester group are ethanolamine, choline, and serine.

14. Phosphoacylglycerols form membranes by arranging
themselves into a lipid bilayer:

15. Sphingolipids They contain an amino alcohol called sphingosine
instead of glycerol:
Sphingolipids are the major lipid component in the myelin sheath, the insulator of nerve cells axons

16. Two of the Most Common Kinds
of Sphingolipids

17. Prostaglandins Prostaglandins are synthesized from arachidonic acid.
They are responsible for regulating a variety of
physiological responses.
They are classified using the formula PGX, where X
designates the functional groups of the five-membered
ring.

18. Examples of prostaglandins and physiological processes they regulate:
Blood pressure
Clotting
Fever
Pain
Labor
Sleep–wake cycle

19. Prostaglandin endoperoxide synthase catalyzes the conversion of arachidonic acid to PGH2.
There are two forms of this enzyme: production under
normal physiological conditions and in response to
inflammation.
The enzyme has a cyclooxygenase activity and a
hydroperoxidase activity.

21. Aspirin (acetylsalicyclic acid) inhibits cyclooxygenase
activity:

22. Other anti-inflammatory drugs also compete with
arachidonic acid or the peroxy radical for the enzyme’s
binding site:

23. Terpenes Terpenes contain carbon atoms in multiples of five.
They are made by joining five-carbon isoprene units.
Oxygen-containing terpenes are sometimes called
terpenoids.
They are a diverse class of lipids.

24. The Isoprene Rule

26. Recognizing the Isoprene Subunit
Zingiberene, oil of ginger
Has three isoprene units

27. Squalene, a triterpene, is a precursor of steroid
molecules:

28. Lycopene and b-carotene are tetraterpenes called
carotenoids:

29. Vitamin A Is a Terpene

31. Isopentenyl pyrophosphate is the starting point for biosynthesis of terpenes:

32. The Conversion of Mevalonic Acid into Mevalonyl Phosphate
an SN2 reaction
a second SN2
Review Sections 26.2 and 26.3

33. Isoprene Biosynthesis: Claisen Condensation
Starred carbon can be 14C
Claisen condensation joins two acetates

34. Isoprene Biosynthesis: Second Claisen Condensation

35. Isoprene Biosynthesis: Leaving Group Elaboration

36. Isoprene Biosynthesis: Elimination and Isomerization
Isopentenyl pyrophosphate
Dimethylallyl pyrophosphate

37. Both isopentyl pyrophosphate and dimethylallyl
pyrophosphate are needed for the biosynthesis of
terpenes

38. Terpene Biosynthesis
Formation of geranyl pyrophosphate:

39. Geranyl Pyrophosphate Formation with 14C-Labels

40. Many monoterpenes can be synthesized from geranyl
pyrophosphate:

41. Formation of Farnesyl Pyrophosphate

42. the Precursor of Cholesterol
Formation of Squalene,
the Precursor of Cholesterol

43. Steroids Steroids are nonpolar compounds and are lipids.
Hormones are chemical messengers.
Many hormones are steroids.
Steroids contain a tetracyclic ring system.

44. Structural Features of Steroids

45. In steroids, the B, C, and D rings are trans fused:
Methyl groups at C-10 and C-13 are called angular
methyl groups

46. The A and B rings are also trans fused in most naturally
occurring steroids:
Substituents on the same side of the steroid ring system as the angular methyl groups are b-substituents.
Those on the opposite side of the plane of the ring
system are a-substituents.

47. Cholesterol Is a Steroid
The most abundant member of the steroid family in
animals
The precursor of all other steroids
More rigid than other membrane lipids

48. Examples of Steroids

50. Examples of Synthetic Steroids