1. Lipids
• Fatty Acids
• Triacylglycerols
• Glycerophospholipids
• Sphingolipids
• Steroids, Eicosanoids
• Lipid Bilayers
Lipids consist of hydrophobic molecules that have great
structural variability and are not polymeric.
In general, the lipids perform three biological functions:
1. Essential components of biological membranes.
2. Contain hydrocarbon chains that serve as energy stores.
3. Involved in many intracellular and intercellular signaling.

2. Fatty Acids
Fatty acids are carboxylic acids with long-chain
hydrocarbon side groups. In plants and animals, the
predominant fatty acid residues have C16 or C18 side
chains.
Type of Fatty Acid
Saturated Fatty Acids
Unsaturated Fatty Acids
Polyunsaturated Fatty Acids
Content of Side Chain
no double bonds
contain double bonds
contain 2 or more double
bonds

3. Common C18 Fatty Acids
HOOC
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH3
CH2
1
HOOC
18
HOOC
1
9 18
HOOC
1
18
9
HOOC
1
18
9
12
12 15
Stearic Acid
18:0
Oleic Acid
18:1
Linoleic Acid
18:2
a-Linolenic Acid
18:3
Fatty acid double bonds are almost always have a cis configuration.

4. Table 9-1. Common Biological Fatty Acids
Common Name Systematic Name Structure
Saturated fatty acids
12:0 Lauric acid Dodecanoic acid CH3(CH2)10COOH
14:0 Myristic acid Tetradecanoic acid CH3(CH2)12COOH
16:0 Palmitic acid Hexadecanoic acid CH3(CH2)14COOH
18:0 Stearic acid Octadecanoic acid CH3(CH2)16COOH
20:0 Arachidic acid Eicosanoic acid CH3(CH2)15COOH
22:0 Behenic acid Docosanoic acid CH3(CH2)20COOH
24:0 Lignoceric acid Tetracosanoic acid CH3(CH2)22COOH
Unsaturated fatty acids (all double bonds are cis)
16:1 Palmitoleic acid 9-Hexadecenoic acid CH3(CH2)5CH=CH(CH2)7COOH
18:1 Oleic acid 9-Octadecenoic acid CH3(CH2)7CH=CH(CH2)7COOH
18:2 Linoleic acid 9,12-Octadecadienoic acid CH3(CH2)4(CH=CHCH2)2(CH2)6COOH
18:3 a-Linolenic acid 9,12,15-Octadecatrienoic acid CH3CH2(CH=CHCH2)3(CH2)6COOH
18:3 -Linolenic acid 6,9,12-Octadecatrienoic acid CH3(CH2)4(CH=CHCH2)3(CH2)3COOH
20:4 Arachidonic acid 5,8,11,14-Eicosatetraenoic acid CH3(CH2)4(CH=CHCH2)4(CH2)2COOH
20:5 EPA 5,8,11,14,17-Eicosapentaenoic
acid
CH3CH2(CH=CHCH2)5(CH2)2COOH
24:1 Nervonic acid 15-Tetracosenoic acid CH3(CH2)7CH=CH(CH2)13COOH

5. Triacylglycerols
H2C
HC
H2C
OH
OH
OH
H2C
HC
H2C
O
O
O
O
C R1
O
C R2
O
C R3
Glycerol Triacylglycerol
O
C
H2C
HC
H2C
O
O
O
O
C
O 18
C
18
16
1-palmitoleoyl-2-linoleoyl-3-stearoyl-glycerol
1
2
3

6. Fats and Oils - Energy Reserves
Fats and oils exist primarily as triacylglycerols (or triglycerides).
Fats are solids at room temperature, oils are liquids.
Fats and oils are complex mixtures of triacylglycerols (composition)
varies with organism). Plant oils are richer in unsaturated fatty acids
(lower melting point and thus are liquids at room temperature).
Fats are a highly efficient form of energy. Fats are less oxidized than
proteins or carbohydrates and thus produce more energy per unit
mass upon complete oxidation. Also, fats are stored anhydrous.
Fats provide about six times the metabolic energy of an equal weight
of hydrated glycogen.
Adipocytes (fat cells) synthesize and store triacylglycerols and
adipose tissue is the most abundant tissue source.

7. Glycerophospholipids
(or phosphoglycerides)
• major component of biological membranes
• esters of glycerol-3-phosphate
O
O
C R1
O
Amphiphilic molecules: nonpolar aliphatic (hydrocarbon) “tails”
polar phosphoryl-X “heads”
H2C
C
H2C
OH
H
O
HO
P OH
OH
H2C
C
H2C
O
H
O
O
P O
O-O
R2 C
X
L-glycerol-3-phosphate general structure of a
glycerophospholipid

8. Common Classes of Phospholipids
X-OH
water
ethanolamine
choline
serine
glycerol
O
Formula of -X
-H
-CH2CH2NH3
+
-CH2CH2N(CH3)3
+
-CH2CH(NH3
+)COO-
-CH2CH(OH)CH2OH
O
C R1
Name
phosphatidic acid
phosphatidylethanolamine
phosphatidylcholine (lecithin)
phosphatidylserine
phosphatidylglycerol
Table 9-2. H2C
C
H2C
O
H
O
O
P O
O-O
R2 C
X

9. Structure of a Phospholipid
1-stearoyl-2-oleoyl-3-phosphatidylcholine
Fig. 9-4
H2C
C
H2C
O
H
O
O
O
C
P O
O-O
(CH2)16CH3
O
C
(CH2)7
CH2CH2N(CH3)3
+
H
C
H
C(CH2)7 H3C

10. Phospholipases hydrolyze phospholipids.
phospholipase A2
O
C R1
O
phospholipase A2
phospholipase A1
O
C R1
O
C R1
O
phospholipase C phospholipase D
H2C
C
H2C
O
H
O
O
P O
O-O
R2 C
X
H2C
C
H2C
O
H
O
HO
P O
O-O
X
H2O
R2COOH
H2C
C
H2C
O
H
O
O
P O
O-O
R2 C
X

11. Phospholipases A2 - phospholipid complex
Fig. 9-6

12. Sphingolipids
• a major membrane component
• derivatives of the C18 amino alcohol sphingosine
• N-acyl fatty acid derivatives are known as ceramides
OH
OH H
H2C C C H
CH
+H3N
HC
(CH2)12
CH3
sphingosine
OH
OH H
H2C C C H
CH
HN
HC
(CH2)12
CH3
C
R
ceramide
O
(R = fatty acid residue)

13. Steroids
A B
C D
cyclopentanoperhydrophenanthrene

14. Cholesterol
HO
cholesterol
Central steroid in
the animal kingdom
Two Functions:
• Serves as an
integral component
in biological
membranes
• Serves as the
biosynthetic
precursor to other
steroid molecules

15. Adrenal Steroidogenesis
HO
cholesterol HO
O
pregnenolone
side chain
cleavage
HO
OH
O
O
OH HO
OH
O
O
O
cortisol aldosterone

16. Sex Hormone Steroidogenesis
HO
cholesterol HO
O
pregnenolone
side chain
cleavage
OH O
O
progesterone
HO
OH
aromatase
O
estradiol testosterone

17. Eicosanoids
• Eicosanoids (C20) are derived from arachidonic acid (20:4)
• Four classes of eicosanoids:
– prostaglandins
– prostacyclins
– thromboxanes
– leukotrienes
1
COOH
8 5
11 14
20
arachidonic acid
(5,8,11,14-eicosatetraenoic acid)

18. Eicosanoid Biosynthesis
COOH
arachidonic acid
phospholipids
phospholipase A2
cyclooxygenase 5-lipooxygenase
O
O
COOH
OH
PGH2
COOH
OH OH
LTB4
(leukotriene)
COOH
OH
HO
HO
COOH
OH
O
HO
COOH
OH
HO
HO O
PGF2a
(prostaglandin) PGI2
(prostacyclin)
TxB2
(thromboxane)