1. Chapter Lipids
15.1 Lipids
15.2 Fatty Acids

2. 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.

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

4. Classes of Lipids
Triglycerides

5. 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.

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

7. 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.

8. 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

9. Melting Points of Some Saturated Fatty Acids

10. Melting Points of Some Unsaturated Fatty Acids

11. 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

12. 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

13. Chapter Lipids
15.3
Waxes, Fats, and Oils 13 13

14. Waxes
Waxes are
esters of saturated fatty acids and long-chain alcohols.
coatings that prevent loss of water by leaves of plants. 14
(pronounced “ho-HO bah” 14

15. Fats and Oils: Triacylglycerols or Triglycerides
Fats and oils are
also called triacylglycerols.
esters of glycerol.
produced by esterification.
Formed when the hydroxyl groups of glycerol react with the carboxyl groups of fatty acids. 15 15

16. Triacylglycerols (Triglycerides)
In a triacylglycerol, glycerol forms ester bonds with three fatty acids.
Ester Bonds 16 16

17. Formation of a Triacylglycerol
Glycerol three fatty acids triacylglycerol +
+ 3H2O 17 17

18. 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. 18 18

19. 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. 19 19

20. Diagram of Triacylglycerol with Unsaturated Fatty Acids
Unsaturated fatty acid chains with kinks cannot pack closely. 20 20

21. Percent Saturated and Unsaturated Fatty Acids In Fats and Oils21 21

22. Chemical Properties of Triacylglycerols (Triglycerides)
Chapter Lipids
15.4
Chemical Properties of Triacylglycerols (Triglycerides) 22 22

23. Chemical Properties of Triacylglycerols (Triglycerides)
The chemical reactions of triacylglycerols 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. 23 23

24. 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. 24 24

25. Hydrogenation Ni + 3H2 Glyceryl tripalmitoleate Glyceryl tripalmitate
(tripalmitolean)
Glyceryl tripalmitate
(tripalmitin) 25 25

26. 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. 26 26

27. 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 27 27

28. 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. 28 28

29. Hydrogenation of Unsaturated Fats29 29

30. 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. 30 30

31. 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. 31 31

32. Hydrolysis In hydrolysis,
triacylglycerols split into glycerol and three fatty acids.
an acid or enzyme catalyst is required. + + 32 32

33. 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. 33 33

34. Saponification
+ 3NaOH + 3
“soap” 34 34

35. Learning Check
Write the product of the following reaction:
+ 3 35 35

36. Solution C O ( H 2 ) 1 4 3 36

37. Glycerophospholipids
Chapter Lipids
15.5
Glycerophospholipids
Fatty acid
Glycerol
Fatty acid
PO4
Amino
alcohol 37 37

38. 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 38 38

39. 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 39 39

40. Structure and Polarity of a Glycerophospholipid40 40

41. Lecithin and Cephalin Lecithin and cephalin are glycerophospholipids
abundant in brain and nerve tissues.
found in egg yolk, wheat germ, and yeast. 41 41

42. Steroids: Cholesterol and Steroid Hormones
Chapter Lipids
15.6
Steroids: Cholesterol and Steroid Hormones 42 42

43. Steroid Nucleus A steroid nucleus consists of 3 cyclohexane rings.
1 cyclopentane ring.
no fatty acids.
steroid nucleus 43 43

44. Cholesterol Cholesterol is the most abundant steroid in the body.
has methyl CH3- groups, alkyl chain, and -OH attached to the steroid nucleus. 44 44

45. 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 45 45

46. Cholesterol in Foods Cholesterol
is considered elevated if plasma cholesterol exceeds 200 mg/dL.
is synthesized in the liver and obtained from foods. 46 46

47. Learning Check Match the components of the cholesterol molecule with
the following:
___ carbon chain ___hydroxyl group
___ steroid nucleus ___methyl group D B A C 47 47

48. 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 48 48

49. Lipoproteins Lipoproteins
combine lipids with proteins and phospholipids.
are soluble in water because the surface consists of polar lipids. 49 49

50. Types of Lipoproteins Lipoproteins
differ in density, composition, and function.
include low-density lipoproteins (LDLs) and high-density lipoproteins (HDLs). 50 50

51. Steroid Hormones Steroid hormones are chemical messengers in cells.
sex hormones.
- androgens in males (testosterone)
- estrogens in females (estradiol)
Adrenocortical hormones from adrenal glands.
- mineralocorticoids (electrolyte balance)
- glucocorticoids (regulate glucose level) 51 51

52. Steroid Hormones Steroid hormones are produced from cholesterol.
include sex hormones such as androgens (testosterone) in males and estrogens (estradiol) in females. 52 52

53. Adrenal Corticosteroids
Steroid hormones called adrenal corticosteroids
are produced by the adrenal glands located on the top of each kidney.
include aldosterone, which regulates electrolytes and water balance by the kidneys.
include cortisone, a glucocorticoid, which increases blood glucose level and stimulates the synthesis of glycogen in the liver. 53 53

54. Anabolic Steroids Anabolic steroids are derivatives of testosterone.
are used illegally to increase muscle mass.
have side effects including fluid retention, hair growth, sleep disturbance, and liver damage. 54 54

55. Adrenal Corticosteroids55 55

56. Learning Check Identify each lipid as a
(1) fatty acid, (2) steroid, or (3) triacylglycerol.
A. cholesterol
B. stearic acid
C. glyceryl tristearate
D. contains no fatty acids 56 56

57. Solution Identify each lipid as a
(1) fatty acid, (2) steroid, or (3) triacylglycerol.
A. 2 cholesterol
B. 1 stearic acid
C. 3 glyceryl tristearate
D. 2 contains no fatty acids 57 57

58. Chapter Lipids
15.7
Cell Membranes 58 58

59. Cell Membranes Cell membranes
separate cellular contents from the external environment.
consist of a lipid bilayer made of two rows of phospholipids.
have an inner portion made of the nonpolar tails of phospholipids with the polar heads at the outer and inner surfaces. 59 59

60. Fluid Mosaic Model of Cell Membranes
The lipid bilayer
contains proteins, carbohydrates, and cholesterol.
has unsaturated fatty acids that make cell membranes fluid-like rather than rigid.
has proteins and carbohydrates on the surface that communicate with hormones and neurotransmitters. 60 60

61. Fluid Mosaic Model of Cell Membranes61 61

62. Transport Through Cell Membranes
The transport of substances through cell membranes
involves
simple diffusion (passive transport), which moves particles from a higher to a lower concentration.
facilitated transport, which uses protein channels to increase the rate of diffusion.
active transport, which moves ions against a concentration gradient. 62 62

63. Transport Pathways Through Cell Membranes
Copyright © by Pearson Education, Inc. 63 63

64. Learning Check The transport of particles across a cell membrane from
high concentration to low concentration is called
1. facilitated transport.
2. simple diffusion.
3. active transport. 64 64

65. Solution The transport of particles across a cell membrane from
high concentration to low concentration is called
2. diffusion. 65 65