Chapter 3. Lipids
Biological lipids are a chemically diverse group of
compounds, which are highly soluble in nonpolar solvents
but not in water. They are either hydrophobic or amphipathic.
I.
II.
III.
IV.
V.
VI.
Introduction
Storage lipids
Structural lipids
Active lipids
Glycolipids and lipoproteins
Separation and analysis of lipids
1
P.79
Considerations
I. Introduction
Classifications
Explanations
Chemical
compositions
Simple lipids
(单纯脂质)
Esters of fatty acids and glycerol
e.g. triacylglycerol, wax
(化学成分)
Compound lipids
(复合脂质)
e.g. phospholipids, glycolipids
Derived lipids
(衍生脂质)
Derived from/related to the above
e.g. fatty acids, steroids, terpenes,
Saponification
Saponifiable lipids
Can be hydrolyzed by KOH
(皂化)
Unsaponifiable lipids
e.g. terpenes, steroids
Polarity (极性)
Polar lipids
Na carboxylate with a long chain
Nonpolar lipids
Ester of long-chain fatty acid and alcohol
Biological
Storage lipids
Energy storage
Functions
Structural lipids
Membrane constituents
(生物功能)
Active lipids
As enzyme cofactors, electron carriers, etc.
2
Membrane structure
3
Amphipathic lipid aggregates that form in water
两亲性
Vesicle
Emulsion
Emulsification
Critical micelle concentration (CMC)
Sodium dodecyl sulfate (SDS)
4
P.80
Lipids
Biological Functions
I. Introduction
Storage lipids
(贮存脂质)
Fatty acids (脂肪酸)
Triacylglycerols (三酰甘油)
Wax (蜡)
Structural lipids
(结构脂质)
Phospholipids (磷脂)
Glycolipids (糖脂)
Sterols (甾醇)
Active lipids
(活性脂质)
Terpenes (萜)
Steroids (类固醇)
Lipoproteins (脂蛋白)
5
II. Storage Lipids
1. Fatty acids (脂肪酸)
2. Triacylglycerols (三酰甘油)
3. Wax (蜡)
6
1. Fatty acids
II. Storage lipids
(1) Compositions & classifications (组成和分类)
(2) Saturated and unsaturated fatty acids (饱和与
不饱和脂肪酸)
(3) Nomencluture (命名)
(4) Fatty acids in food
(5) Essential fatty acids (必需脂肪酸)
(6) Physical properties
(7) Chemical properties
7
(1). Compositions & classifications
(组成和分类)
Saturated
(饱和脂肪酸)
‘Tail’ – hydrophobic chain (C4-C36)
疏水长链
Fatty acid
亲水基团
‘Head’ – hydrophilic group (-COO-)
Monounsaturated
(单不饱和脂肪酸)
Unsaturated
(不饱和脂肪酸)
Polyunsaturated
(多不饱和脂肪酸)
Most common:
Even No. of C (偶数C)
Unbranched (无支链)
C12-C24
8
(2). Saturated and unsaturated fatty acids
II. Storage lipids
Saturated fatty acids (饱和脂肪酸):
 Flexible structure, with the fully extended conformation the
most stable (结构灵活)
 Close packing (紧密堆积)
 High melting point (高熔点, e.g. beef oil)
Unsaturated fatty acids (不饱和脂肪酸) :
 Slightly more abundant in nature
 ‘Kinks’ in the chain – resulting in flexible, fluid aggregates
 The most common one is oleic acie (油酸): 18:1 9c
 C=C bond usually in cis-form, rarely in trans-form
 Common location of C=C bonds:
Monounsaturated: C9=C10
Polyunsaturated:
C9=C10, C12=C13, C15=C16,
9
(3). Nomencluture (命名)
Common name
(俗名)
Systematic name
(系统名)
Symbol
(符号)
Stearic acid
硬脂酸
n-Octadecanoic acid
(n-十八酸)
Linoleic acid
亚油酸
cis, cis-9,1218:29c,12c
octadecadienoic acid
(十八碳-9,12-二烯酸)
Chain length
(链长,总C数)
18:0
Structure
(结构)
CH3(CH2)16COOH
Saturated
(饱和)
CH3(CH2)4(CH=CHCH2)2 Unsaturated
(CH2)6COOH
(不饱和)
18:29c,12c
cis-trans configuration of C=C
(双键的顺反构型)
No. of C=C bonds
(双键数)
Position of C=C bonds
(双键的位置)
10
11
(4). Fatty acids in food
 Vegetable oils
vs. animal oils and fats
 Unsaturated fatty acids vs. saturated fatty acids
 Unsaturated fatty acids: cis vs. trans
 Trans fat and hydrogenated vegetable oil
Example 1. Olive oil – rich in oleic acid (monounsaturated)
Example 2. Margarine – a substitute for butter
II. Storage lipids
Source
月桂酸，豆蔻酸 棕榈酸 硬脂酸
油酸
亚油酸
12:0, 14:0
16:0
18:0
18:19c
18:29c,12c
Beef
5
24-32
20-25
37-43
2-3
Coconut
74
10
2
7
Olive
9
2
84
4
Sunflower
6
1
21
66
12
Partial hydrogenation of
cooking oils
shelf lives  (∵m.p.)
 trans fatty acids 
Higer incidence of
cardiovascular
disease
13
棕榈酸
(5). Essential fatty acids
棕榈油酸
(EFA, 必需脂肪酸)
硬脂酸
— those that are not synthesized
by mammals and yet are
necessary for normal growth
and life.
油酸
亚油酸
Eicosapentaenoic acid (EPA)
20:5(5,8,11,14,17)
十二碳五烯酸
Docosahexaenoic acid (DHA)
22:6(4,7,10,13,16,19)
二十二碳六烯酸
ALA,亚麻酸
花生四烯酸
Omega-3 (-3) fatty acids
Polyunsaturated fatty acids (PUFAs) with a double bond
between C3 and C4 from the methyl end of the chain.
Specially important in human nutrition
Optimal dietary ratio:
-6 PUFAs
= 1:1 ~ 4:1
-3 PUFAs
亚麻酸，18:3(9,12,15):
-linolenic acid (ALA), an -3 fatty acid
-linolenic acid (GLA), an -6 fatty acid
15
Essential fatty acid
Humans can synthesize
EPA and DHA from ALA
-linolenic acid (ALA)
18:3(9,12,15)
亚麻酸
Eicosapentaenoic acid (EPA)
20:5(5,8,11,14,17)
十二碳五烯酸
All the 3 are -3 fatty acids, all
important in cellular function.
Docosahexaenoic acid (DHA)
22:6(4,7,10,13,16,19)
16
二十二碳六烯酸
(6) Physical properties (物理性质)
Carboxylic head
(羧基头)
Hydrocarbon tail
(烃链)
Modified, e.g. esterified
(如：脂肪酸酯化)
Solubility 
(溶解度)
Chain length 
(烃链长度)
Unsaturation degree 
(烃链的不饱和程度)
Melting point 
(熔点)
Fatty acid
6:0
12:0
Solubility
9.7 mg/g
0.055 mg/g
Fatty acid
m.p.
Fatty acid
m.p.
18:0
69.6oC
14:0
53.9oC
18:0
0.003 mg/g
18:19c
13.4oC
14:19c
4.5oC
17
P.86
(7). Chemical properties
 Oxidation
II. Storage lipids
(氧化) and peroxidation (过氧化)
 Addition (加成)
 Hydrogenation (氢化)
 Halogenation (卤化)
 Emulfication (乳化): Amphipathy (两亲性)
Emulsifier (乳化剂)
Detergent (去污剂)
Surfactant (表面活性剂)
O
十二烷基硫酸钠
(Sodium dodecyl sulfate, SDS)
Ionic detergent
O
S
+
O- Na
O
18
P.91
2. Triacylglycerols (三酰甘油)
1). Triacylglycerol (三酰甘油) = Triglyceride (甘油三脂), TG
-- Triester of glycerol with 3 fatty acids (甘油和脂肪酸形成的三酯)
2). The central C is a prochiral center
O
-- sn-system
H2C
OH
H2C
O
C
R1
O
3). Classification:
HC
O
C
R2
Simple triacylglycerol (简单三酰甘油) HC OH
O
Triolein (三油酸甘油脂)
H2C
OH
H2C
O
C
R3
Tristearin (三硬脂酸甘油脂)
Triacylglycerol
Mixed triacylglycerol (混合三酰甘油) Glycerol
1-棕榈酰-2-硬脂酰-3-豆蔻酰-sn-甘油
简单三酰甘油: R1 = R2 = R3
混合三酰甘油: R1, R2, R3不完全相同
Monoacylglycerol (单酰甘油)
Diacylglycerol (二酰甘油)
Triacylglycerol (三酰甘油)
19
Nomencluture of glycerol derivatives: sn-system
(Stereospecific numbering system)
CH2-OPO3-
CH2OH
HO
C

H
C
H
CH2-OPO3-
CH2-OPO3-
OH
C
HO
CH2OH
L-Glycerol-3-phosphate
CH2OH
D-Glycerol-1-phosphate
sn-Glycerol-1-phosphate
sn-Glycerol-3-phosphate
a
C
sn-甘油-3-磷酸
OH
C2
CaH2OH
HO
C2
Ca
H
CbH2OH
L-configuration
OH
C
2
Cb
S
y inc
lightl
S l ig h
r e a se
t ly in
c r ea s
th
H
a
C
f
o
rity
e prio
e the
priori
ty o f
Cb
S-configuration at C2
Ca -- Pro-S
Cb
Ca is denoted as C1
R-configuration at C2
Ca
OH
C2
Cb
Cb -- Pro-R
Cb is denoted as C3
General structrure of a triacylglycerol
Hydrolysis by:
Oil (油) – liquid
Fat (脂) – solid
H+
OHLipases (脂肪酶)
21
P.93
2. Triacylglycerols (continued)
4) Physical properties (物理性质):
a. Color and odor (颜色和气味)
Colorless, odorless, tasteless
b. Density and solubility (密度和溶解度)
II. Storage lipids
Density < 1 g/cm3
Insoluble in H2O, soluble in nonpolar solvents
TGs are nonpolar, hydrophobic molecules:
c. Melting point (熔点)
Chain length, m.p.
Double bonds, m.p.
Olive oil – liquid
Beef fat – solid
22
P.94
2. Triacylglycerols (continued)
5) Chemical properties (化学性质):
a. Hydrolysis (水解) and saponification (皂化)
-- Saponification value (皂化值)
-- Used for estimation of the molecular weight (用于估计分子量).
b. Hydrogenation (氢化) and halogenation (卤化)
-- Iodine value (碘值)
-- Used for estimation of the unsaturation degree (用于估计不饱和度).
II. Storage lipids
c. Acetylation (乙酰化)
-- Acetylation number (乙酰值)
-- Used for estimation of the number of free –OH (用于估计自由羟基数)
d. Rancidity (酸败) and autoxidation (自动氧化)
-- Acid value (酸值)
-- Used for estimation of the rancidity degree (用于估计酸败程度)
23
Saponification value (皂化值)
x
y
 Saponification value is the mg of KOH required to
saponify 1g of a TG (皂化值是皂化1g三酰甘油所需要
的KOH的mg数).
 It can be used to estimate the molecular weight of a TG
(皂化值可帮助估计三酰甘油的分子量).
O
H2C
O
C
O
R1
HC
O
R2
H2C
O
C
O
C
+ 3 KOH
R3
皂化值
Triacylglycerol
1
分子量
y
:
H2C
OH
HC
OH
H2C
OH
R1COO+
R2COOR3COO-
Glycerol
x/1000
KOH
= 1: 3
24
Iodine value (碘值)
x
y
 The iodine value represents how many grams of I2 are
required for the halogenation reaction of 100 g of a TG
(碘值指100g油脂卤化时所能吸收碘的克数)
 It can be used to estimate the unsaturation level of the
TG (碘值可用于估计油脂的不饱和度)
Suppose the TG contains y double bonds,
C
+
C
CI
I2
CI
碘值
100
MW
TG分子量
:
x
I2
= 1:y
TG不饱和键数
25
Acetylation number (乙酰值)
x

y

R-OH
It is the mg of KOH required to neutralize the CH3COOH
released from 1 g of an acetylated product (乙酰值指从1g
油脂乙酰化产物中释放的乙酸所需的KOH的mg数).
It is used to represent how many hydroxyl groups are
available in the TG (用于表示油脂的羟基化程度).
Acetylation
乙酰化
CH3COOR
Hydrolysis
水解
CH3COOH : KOH
乙酰值
1
x/1000
:
MW
TG分子量
KOH
TG的自由羟基数
= 1: y
26
Acid value (酸值)


It is the mg of KOH required to neutralize the free fatty
acids released from 1 g of a TG (酸值是中和1 g油脂
中的游离脂肪酸所需的KOH的mg数)
It is used to estimate the rancidity degree of the TG (用
于估计油脂的酸败程度)
Two major reasons for rancidification (酸败):
 Autoxidation (自氧化)
 Microbial effects (微生物效应)
27
2. Triacylglycerols (continued)
6) Major use of TGs in animals and plants
Energy storage
 Insulation
 Examples: Polar bears & Sperm whales

II. Storage lipids
The mighty whales swim in a sea of water,
and have a sea of oil swimming in them.
28
Triglycerols vs. starch/glycogen
2 advantages of using triglycerols as stored fuels
 More reduced  more energy to be released
when oxidized
 More hydrophobic  no need to carry extra
water for hydration
Fats – to meet energy needs for months
The human body can store
Glycogen – less than a day’s energy supply
Glucose and glycogen can work as quick sources
of metabolic energy (∵ready solubility in water)
29
3. Wax
P.95
1) Esters of long-chain fatty acids with long-chain
alcohols
2) Energy stores and water repellents
3) Applications
Weakly polar head group
II. Storage lipids
C14-C36
C16-C36
Nonpolar tails
Triacontanoylpalmitate, the major component of beeswax
30
A honeycomb constructed of beeswax
31
III. Structural Lipids
1.
2.
3.
4.
5.
Glycerophospholipids (甘油磷脂)
Glycolipids (糖脂)
Archaeal ether lipids (古细菌醚脂)
Sphingolipids (鞘脂类)
Sterols (甾醇)
32
Principal classes of storage and membrane lipids
膜脂
鞘氨醇
古细菌醚脂
糖脂
磷脂
三酰甘油 甘油磷脂
phosphosphingolipids
鞘磷脂
（鞘氨醇磷脂）
glycosphingolipids
鞘糖脂
Sphingolipids
(鞘脂类)
Sterols (甾醇)
33
P.103
1. Glycerophospholipids (甘油磷脂)
Glycerophospholipids (甘油磷脂)
‖
Phosphoglycerides (磷酸甘油脂)
III. Structural Lipids
D-Glycerol 3-phosphate, the
backbone of phospholipids
C-1: C16 or C18, saturated fatty acid
Nonpolar tail (非极性尾部)
O
C
O
C
O
O
CH2
CH
H2C
C-2: C18 or C20, unsaturated fatty acid
O
O
P
O
X
O-
Polar head
(极性头)
34
两亲性
手性
电荷
磷脂酸
磷脂酰乙氨醇
(脑磷脂)
cephalin
磷脂酰胆碱
(卵磷脂)
lecithin
The charge on the polar head contributes greatly
to the surface properties of membranes
35
2. Glycolipids (糖脂)
 Galactolipids (半乳糖脂) and
sulfolipids (硫脂) are
predominate in plant cells.
 Galactolipids are localized in
the thylakoid (类囊体)
membranes of chloroplasts,
making up 70-80% of the total
membrane lipids of a vascular
plant.
 Galactolipids are probably the
most abundant membrane
lipids in the biosphere.
3 glycolipids of chloroplast thylakoid
membranes
36
3. Archaeal ether lipids (古细菌醚脂)
 Archaea contain unique membrane lipids – ether lipids.
 The general name for these lipids: glycerol dialkyl glycerol
tetraethers (GDGTs)
 These ether linkages are much more stable to hydrolysis at low
pH and high temperature.
 Archaea live in ecological niches with extreme conditions: e.g.,
high temperature, low pH, high ionic strength.
Long chain (32 carbons) branched hydrocarbons
A typical membrane lipid of archaea
37
4. Sphingolipids (鞘脂类)
Sphingosine (鞘氨醇) as the backbone
HO
CH
III. Structural Lipids
HC
H2C
CH=CH
O
H
N
C
O
(CH2)12-CH3
两亲性
手性
电荷
Fatty acid chain
X
神经酰胺 (ceramide)：X = H
鞘磷脂 (phosphosphingolipid): X = 磷酰胆碱，磷酰乙醇胺
鞘糖脂 (glycosphingolipid): X = 单糖，寡糖
Sphingolipids at cell surfaces are sites of biological recognition
38
P.107
Phosphosphingolipids 鞘氨醇磷脂
(Sphingomyelin 鞘磷脂)
HO – CH – CH = CH – (CH2)12 – CH3
O
Sphingosine
CH – NH – C – (CH2)14 – CH3
(鞘氨醇)
O
Fatty acid
(脂肪酸)
CH2 – O – P – O – CH2 – CH2 – N+(CH3)3
O-
Phosphocholine
(磷酰胆碱)
Sphinogomyelins are present in the plasma
membranes of animal cells and are especially
prominent in myelin, a membranous sheath that
surrounds and insulates the axons of some neurons –
thus the name “sphingomyelins”.
39
神经酰胺
Sphinogolipids
Phosphosphinogolipid
(神经)鞘磷脂
(鞘磷脂)
脑苷脂
Glycosphingolipids
(鞘糖脂)
红细胞糖苷酯
神经节苷脂
40
Glycosphingolipids as determinants of blood groups
P.63
血型 红细胞
血清
III. Structural Lipids
凝集原
凝集素
抗原
抗体
A
A
抗B
B
B
抗A
AB
A, B
O
抗A, 抗B
Type O blood – universal donor
Type AB blood – universal receiver
41
P.105
Phospholipids and sphingolipids are degraded
in lysosomes (细胞溶酶体)
Phospholipase A1
H+, OH-
O
III. Structural Lipids
CH2 – O – C – R1
O
R2 – C – O – CH
H+, OH-
Phospholipase
磷脂酶
O
CH2 – O – P – O – X
Phospholipase A2
H+
O-
Phospholipase C
H+, Strong OH-
Phospholipase D
42
Sphingomyelins and
gangliosides are
degraded by a set of
lysosomal enzymes.
A genetic defect in any
of these enzymes may
lead to severe medical
consequences.
43
Fatal diseases related to
genetic lipid storage disorder
Disease
Niemann-Pick
Tay-Sachs
Sphingomyelinase -Hexosaminidase A
Deficient enzyme
Accumulated substance
Sphingomyelin
Ganglioside
Prognosis
Early death
Early death
鞘磷脂
鞘糖脂
44
P.112
5. Sterols (甾醇)
 structural lipids present in the membranes of most eukaryotic cells
Cholesterol (胆固醇)
Sterol’s roles
 Major constituents of plasma
membrane and plasma lipoproteins
(细胞质膜和脂蛋白的主要组成)
 Precursors of other steroids (生成其
它类固醇的前体)
(牛磺胆酸)
(胆汁酸)
Cholesterol is the major sterol in animal tissues.
Bacteria cannot synthesize sterols.
45
Steroids derived from cholesterol
(从胆固醇衍生出来的类固醇)
5 families of hormones
睾丸激素
雌二醇
皮质(甾)醇
醛甾酮
脱氢皮质(甾)醇 肾上腺皮质激素
Androgens (雄性激素) –
testosterone (睾丸激
素)
Estrogens (雌激素) –
estradiol (雌二醇)
Progestins (孕激素) –
progesterone (孕酮)
Glucocorticoids (糖(肾上
腺)皮质激素) –
cortisol
Mineralocorticoids (盐皮
质激素)
黄铜质
强的松
46
IV. Active Lipids
 Signals – e.g. Steroid hormones, vitamins A & D
 Cofactors/electron carriers – e.g. coenzyme A, vitamins E & K
 Pigments – e.g. -carotene (胡萝卜素)
 A large group of volatile lipids produced in plants serve as
signals passing through the air
角黄素
玉米黄质
47
P.110
Terpenes and steroids
(萜和类固醇)
 Active lipids (活性脂质)
 Unsaponifiable lipids (非皂化脂)
 Different from other lipids: containing no fatty acids (不含
脂肪酸)
 Terpenes: composed of isoprene units (异戊二烯单位)
 Steroids: composed of steroid nucleus (甾核)
Zoosterol
(动物固醇)
Cholesterol
(胆固醇)
Phytosterol
(植物固醇)
-sitosterol
(谷固醇)
Sterols (甾醇)
48
Head-to-tail linkage
P.110-112
H
Terpenes (萜)
CH2
C

C
H2C
CH3
Isoprene (C5)
Tail-to-tail linkage
Monoterpene (C10) – 单萜
Sesquiterpene (C15) – 倍半萜
Diterpene (C20) – 双萜
Tetraterpene (C40) – 四萜
Lycopene (C40, 番茄红素)
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Some biologically active isoprenoid compounds or derivatives
杀鼠灵
IV. Active Lipids
泛醌,辅酶Q
质体醌
长醇
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V. Glycolipids and Lipoproteins
(糖脂和脂蛋白)

Glycolipids (糖脂):
III. Structural Lipids
Compounds formed by covalent linkage of lipids
and saccharides via glycosidic bonds
(糖和脂通过糖苷键相连)

Lipoproteins (脂蛋白):
Complexes formed by noncovalent interaction
between lipids and proteins
(脂和蛋白质之间非共价结合)
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Glycolipids (糖脂)
III. Structural Lipids
Glycolipids are also membrane lipids
-- serving as structural constituents in the cell
-- providing sites for biological recognition
Glyceroglycolipids (甘油糖脂)
 Glycosphingolipids (鞘糖脂)

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Lipoproteins (脂蛋白)
P.116

III. Structural Lipids

Lipoproteins are aggregrates of lipids and proteins (脂蛋白
是脂和蛋白质的非共价结合物)
 Noncovalent interactions (非共价结合)
 Present in plasma -- also called plasma lipoproteins (血
浆脂蛋白)
 Role: to carry water-insoluble lipids in blood (在血液
中运载非水溶性的脂)
Apolipoproteins (载脂蛋白)
 To increase solubility of the hydrophobic lipids (增加
脂的溶解度)
 To act as specific sites for recognition by the
lipoprotein acceptors (为脂蛋白受体提供识别位点)
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P.117
Classifications of lipoproteins
As signals
Classification
Density
Chylomicron
(乳糜微粒)
0.92~0.96
Very low density
lipoprotein
VLDL
0.95~1.006
Intermediate
density lipoprotein
IDL
1.006~1.019
Low density
lipoprotein
LDL
1.019~1.063
High density
lipoprotein
HDL
1.063~1.21
Densities:
Proteins – 1.3-1.4 g/cm3
Lipids – 0.8-0.9 g/cm3
Diameter:
100-500 nm
80% of mass
Molecular structure of a chylomicron
(乳糜微粒的结构)
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VI. Separation and Analysis
of Lipids
1. Lipid extraction (萃取)
2. Adsorption chromatography (吸附层析)
3. Thin layer chromatography (薄层层析)
4. Gas-liquid chromatography (气相色谱)
5. High-performance liquid
chromatography (高压液相色谱)
6. Specific hydrolysis (专一性水解)
7. Mass spectrometry (质谱)
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