1. Chemeketa Community College
Chapter 15:
Lipids
Larry Emme
Chemeketa Community College

2. Chapter Outline Lipids Fatty Acids Waxes, Fats, & Oils
Chemical Properties

3. Lipids
Lipids are
biomolecules that contain fatty acids or a steroid nucleus.
soluble in organic solvents, but not in water.
named for the Greek word lipos, which means “fat.”
extracted from cells using organic solvents.

4. Types of Lipids The types of lipids containing fatty acids are waxes
fats and oils called triglycerides (triacylglycerols)
glycerophospholipids
prostaglandins
The types of lipids that do not contain fatty acids are
steroids

5. Classes of Lipids
Triglycerides

6. Fatty Acids Fatty acids are long-chain carboxylic acids.
typically carbon atoms.
insoluble in water.
saturated or unsaturated.
Olive oil contains 84% unsaturated fatty acids and 16% saturated fatty acids.

7. Saturated and Unsaturated Fatty Acids
Fatty acids are
saturated with all single C–C bonds.
unsaturated with one or more double C=C bonds.

8. Properties of Saturated Fatty Acids
contain only single C–C bonds.
are closely packed.
have strong attractions between chains.
have high melting points.
are solids at room temperature.

9. Properties of Unsaturated Fatty Acids
contain one or more cis double C=C bonds.
have “kinks” in the fatty acid chains.
do not pack closely.
have few attractions between chains.
have low melting points.
are liquids at room temperature.
“kinks” in chain

10. Melting Points of Some Saturated Fatty Acids

11. Melting Points of Some Unsaturated Fatty Acids

12. Learning Check stearic acid (18 C) saturated
Assign the melting points of –17 °C, 13 °C, and 69 °C to the correct fatty acid. Explain.
stearic acid (18 C) saturated
oleic acid (18 C) one double bond
linoleic acid (18 C) two double bonds

13. Solution
Stearic acid is saturated and would have a higher melting point than the unsaturated fatty acids. Because linoleic has two double bonds, it would have a lower mp than oleic acid, which has one double bond.
stearic acid mp 69 °C saturated
oleic acid mp 13 °C
linoleic acid mp -17 °C most unsaturated

14. Waxes, Fats, and Oils 14 14

15. Waxes
Waxes are
esters of saturated fatty acids and long-chain alcohols.
coatings that prevent loss of water by leaves of plants. 15
(pronounced “ho-HO bah” 15

16. Fats and Oils: Triglycerides or Triacylglycerols
Fats and oils are
also called triglycerides.
esters of glycerol.
produced by esterification.
Formed when the hydroxyl groups of glycerol react with the carboxyl groups of fatty acids. 16 16

17. Triglycerides (Triacylglycerols)
In a triglyceride, glycerol forms ester bonds with three fatty acids.
Ester Bonds 17 17

18. Formation of a Triglyceride
Glycerol three fatty acids triglyceride +
+ 3H2O 18 18

19. Melting Points of Fats and Oils
A fat
is usually solid at room temperature.
is prevalent in meats, whole milk, butter, and cheese.
An oil
is usually liquid at room temperature.
is prevalent in plants such as olive and safflower. 19 19

20. Oils with Unsaturated Fatty Acids
have more unsaturated fats.
have cis double bonds that cause “kinks” in the fatty acid chains.
with “kinks” in the chains do not allow the triacylglycerol molecules to pack closely.
have lower melting points than saturated fatty acids.
are liquids at room temperature. 20 20

21. Diagram of Triglyceride with Unsaturated Fatty Acids
Unsaturated fatty acid chains with kinks cannot pack closely. 21 21

23. Percent Saturated and Unsaturated Fatty Acids In Fats and Oils23 23

24. 7 61 32 8 77 15 9 16 75 12 16 72 13 29 58 15 75 10 15 23 62 19 48 33 27 19 54 43 47 10 51 38 11 68 28 4 91 7 2

25. Chemical Properties of Triglycerides25 25

26. Chemical Properties of Triglycerides
The chemical reactions of triglycerides are similar
to those of alkenes and esters.
In hydrogenation, double bonds in unsaturated fatty acids react with H2 in the presence of a Ni or Pt catalyst.
In hydrolysis, ester bonds are split by water in the presence of an acid, a base, or an enzyme. 26 26

27. Hydrogenation of Oils The hydrogenation of oils adds hydrogen (H2) to
the carbon atoms of
double bonds.
converts double bonds
to single bonds.
increases the melting point.
produces solids, such as margarine and shortening. 27 27

28. Hydrogenation Ni + 3H2 Glyceryl tripalmitoleate Glyceryl tripalmitate
(tripalmitolean)
Glyceryl tripalmitate
(tripalmitin) 28 28

29. OlestraTM, a Fat Substitute
Olestra is
used in foods as an artificial fat.
sucrose linked by ester bonds to several long-chain fatty chains.
not broken down in the intestinal tract. 29 29

30. Cis and Trans Fatty Acids
Unsaturated fatty acids can be
cis with bulky groups on same side of C=C.
CH3─ (CH2) (CH2)7─ COOH cis
C=C
H H
trans have bulky groups on opposite sides of C=C.
CH3─ (CH2) H
C=C trans
H (CH2)7─ COOH 30 30

31. Hydrogenation and Trans Fatty Acids
Most naturally occurring fatty acids have cis double
bonds.
During hydrogenation, some cis double bonds are converted to trans double bonds.
In the body, trans fatty acids behave like saturated fatty acids.
It is estimated that 2-4% of our total Calories is in the form of trans fatty acid.
Several studies reported that trans fatty acids raise LDL-cholesterol and lower HDL-cholesterol. 31 31

32. Hydrogenation of Unsaturated Fats32 32

33. Learning Check (1) True or (2) false:
A. There are more unsaturated fats in vegetable oils.
B. Vegetable oils have higher melting points than fats.
C. Hydrogenation of oils converts some cis-double bonds to trans-double bonds.
D. Animal fats have more saturated fats. 33 33

34. Solution (1) True or (2) false:
A. T There are more unsaturated fats in vegetable oils.
B. F Vegetable oils have higher melting points than fats.
C. T Hydrogenation of oils converts some cis-double bonds to trans- double bonds.
D. T Animal fats have more saturated fats. 34 34

35. Hydrolysis In hydrolysis,
triglycerides split into glycerol and three fatty acids.
an acid or enzyme catalyst is required. + + 35 35

36. Saponification and Soap
is the reaction of a fat with a strong base.
splits triacylglycerols into glycerol and the salts of fatty acids.
is the process of forming “soaps” (salts of fatty acids).
with KOH gives softer soaps. 36 36

37. Saponification
+ 3NaOH + 3
“soap” 37 37

38. Learning Check
Write the product of the following reaction:
+ 3 38 38

39. Solution C O ( H 2 ) 1 4 3 39

40. Glycerophospholipids
Fatty acid
Glycerol
Fatty acid
PO4
Amino
alcohol 40 40

41. Glycerophospholipids
Glycerophospholipids are
the most abundant lipids in cell membranes.
composed of glycerol, two fatty acids, phosphate, and an amino alcohol.
Fatty acid
Glycerol
Fatty acid
PO4
Amino
alcohol 41 41

42. Polarity of Glycerophospholipids
A glycerophospholipid has
two nonpolar fatty acid chains.
a phosphate group and a polar amino alcohol.
CH3 │
HO−CH2−CH2−N−CH HO−CH2−CH2−NH3 │
Choline CH Ethanolamine +
NH3
│ Amino alcohols
HO−CH2−CH−COO− Serine 42 42

43. Structure and Polarity of a Glycerophospholipid43 43

44. Lecithin and Cephalin Lecithin and cephalin are glycerophospholipids
abundant in brain and nerve tissues.
found in egg yolk, wheat germ, and yeast. 44 44

45. Steroids: Cholesterol and Steroid Hormones45 45

46. Steroid Nucleus A steroid nucleus consists of 3 cyclohexane rings.
1 cyclopentane ring.
no fatty acids.
steroid nucleus 46 46

47. Cholesterol Cholesterol is the most abundant steroid in the body.
has methyl CH3- groups, alkyl chain, and -OH attached to the steroid nucleus. 47 47

48. Cholesterol in the Body
A normal, open artery.
Cholesterol
is obtained from meats, milk, and eggs.
is synthesized in the liver.
is needed for cell membranes, brain and nerve tissue, steroid hormones, and vitamin D.
clogs arteries when high levels form plaque.
An artery clogged by cholesterol plaque 48 48

49. Cholesterol in Foods Cholesterol
is considered elevated if plasma cholesterol exceeds 200 mg/dL.
is synthesized in the liver and obtained from foods. 49 49

50. Learning Check Match the components of the cholesterol molecule with
the following:
___ carbon chain ___hydroxyl group
___ steroid nucleus ___methyl group D B A C 50 50

51. Solution Match the components of the cholesterol molecule with
the following:
_D carbon chain _A_hydroxyl group
_C steroid nucleus _B_methyl group D B A C 51 51

52. Solution Identify each lipid as a
(1) fatty acid, (2) steroid, or (3) triglyceride.
A. 2 cholesterol
B. 1 stearic acid
C. 3 glyceryl tristearate
D. 2 contains no fatty acids 52 52

53. The End

54. End of Chapter Learning Checks Try these after you have reviewed the chapter

55. Learning Check
What characteristic do all lipids have in common? 55 55

56. Learning Check Answers
What characteristic do all lipids have in common?
All lipids are insoluble in water. 56

57. Learning Check
Which fatty acid would you predict to have the lowest melting point? 57

58. Learning Check Answers
Which fatty acid would you predict to have the lowest melting point?
Both fatty acids are saturated. The fatty acid with the fewest number of carbon atoms should have the lowest melting point. 58

59. Learning Check
The trans isomers of palmitoleic acid CH3(CH2)5CH=CH(CH2)7COOH is shown below.
Draw the cis isomer.
trans-isomer 59

60. Learning Check Answers
The trans isomers of palmitoleic acid CH3(CH2)5CH=CH(CH2)7COOH is shown below.
Draw the cis isomer.
trans-isomer
cis-isomer 60

61. CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH
Learning Check
What is the correct classification of the fatty acid shown below?
CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH
ω-3
ω-6 61

62. CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH
Learning Check Answers
What is the correct classification of the fatty acid shown below?
CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH
ω-3
ω-6
The double bond is attached to the sixth carbon from the end of the molecule furthest from the carboxyl group. This is an ω-6 fatty acid. 62

63. Learning Check
What is the classification of the following lipid? 63

64. Learning Check Answers
What is the classification of the following lipid?
This lipid is an example of a phospholipid. 64

65. Learning Check
What is the classification of the following lipid? 65

66. Learning Check Answers
What is the classification of the following lipid?
This molecule is a glycolipid. 66

67. Learning Check
Identify the functional groups in cortisone. 67

68. Learning Check Answers
Identify the functional groups in cortisone. 68