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05 Lecture Presentation lipid

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Concept 5.3: Lipids are a diverse group of
hydrophobic molecules
• Lipids are the one class of large biological molecules that
do not form polymers
• The unifying feature of lipids is having little or no affinity(a
spontaneous or natural liking or sympathy for someone or something) for water
• Lipids are hydrophobic because they consist mostly of
hydrocarbons, which form nonpolar covalent bonds
• The most biologically important lipids are fats,
phospholipids, and steroids 类固醇
•
Hydrophobic /ˌhīdrəˈfōbik/ tending to repel or fail to mix with water
•
Hydrocarbon /ˌhīdrəˈkärbən/ a compound of hydrogen and carbon, such as any of those which are the chief components of
petroleum and natural gas
•
Phospholipids /ˌfäsfōˈlipid/ a lipid containing a phosphate group in its molecule, e.g., lecithin
•
Steroids /ˈsterˌoid,ˈstirˌoid/ any of a large class of organic compounds with a characteristic molecular structure containing four
rings of carbon atoms (three six-membered and one five). They include many hormones, alkaloids, and vitamins
Fats
•
Fats are constructed from two types of smaller molecules: glycerol and fatty acids
•
Glycerol is a three-carbon alcohol with a hydroxyl group attached to each carbon
•
A fatty acid consists of a carboxyl group attached to a long carbon skeleton
•
Glycerol /ˈɡlisərôl,ˈɡlisəräl/
•
甘油
•
Hydroxyl /hīˈdräksəl/
•
Carboxyl /kärˈbäksəl/ of or denoting the acid radical —COOH, present in most organic
acids.
•
Fatty acid /ˈfadē ˈasəd/ a carboxylic acid consisting of a hydrocarbon chain and a
terminal carboxyl group, especially any of those occurring as esters in fats and oils. 脂肪
酸
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 5-11
Fatty acid
(palmitic acid)
Glycerol
(a) Dehydration reaction in the synthesis of a fat
Ester linkage
(b) Fat molecule (triacylglycerol)
Fig. 5-11a
Fatty acid
(palmitic acid)
Glycerol
(a) Dehydration reaction in the synthesis of a fat
Fig. 5-11b
Ester linkage
(b) Fat molecule (triacylglycerol)
•
Fats separate from water because water molecules form
hydrogen bonds with each other and exclude the fats
•
In a fat, three fatty acids are joined to glycerol by an ester
linkage, creating a triacylglycerol, or triglyceride
Ester:/ˈestər/ an organic compound made by replacing the hydrogen of an acid by an alkyl or
other organic group. Many naturally occurring fats and essential oils are esters of fatty acids
Triacylglycerol:
Triglyceride:/trīˈɡlisəˌrīd/ A triglyceride is an ester derived from
glycerol and three fatty acids. Triglycerides are the main
constituents of body fat in humans and other vertebrates, as well
as vegetable fat 甘油三酸酯
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• Fatty acids vary in length (number of carbons)
and in the number and locations of double
bonds
• Saturated fatty acids have the maximum
number of hydrogen atoms possible and no
double bonds
• Unsaturated fatty acids have one or more
double bonds
Animation: Fats
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 5-12
Structural
formula of a
saturated fat
molecule
Stearic acid, a
saturated fatty
acid
(a) Saturated fat
Structural formula
of an unsaturated
fat molecule
Oleic acid, an
unsaturated
fatty acid
(b) Unsaturated fat
cis double
bond causes
bending
Fig. 5-12a
Structural
formula of a
saturated fat
molecule
Stearic acid, a
saturated fatty
acid
(a) Saturated fat
Fig. 5-12b
Structural formula
of an unsaturated
fat molecule
Oleic acid, /ōˌlēik ˈasəd/ an
unsaturated
fatty acid油酸
(b) Unsaturated fat
cis double
bond causes
bending
• Fats made from saturated fatty acids are called
saturated fats, and are solid at room
temperature
• Most animal fats are saturated
• Fats made from unsaturated fatty acids are
called unsaturated fats or oils, and are liquid at
room temperature
• Plant fats and fish fats are usually unsaturated
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
•
A diet rich in saturated fats may contribute to cardiovascular
/ˌkärdēōˈvaskyələr/ disease through plaque /plak/ deposits. Relating to
the heart and blood vessels 心血管的. a sticky deposit on teeth in which
bacteria proliferate
•
Hydrogenation is the process of converting unsaturated fats to saturated
fats by adding hydrogen
•
Hydrogenating vegetable oils also creates unsaturated fats with trans
double bonds
•
These trans fats may contribute more than saturated fats to
cardiovascular disease
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• The major function of fats is energy storage
• Humans and other mammals store their fat in
adipose /ˈadəˌpōs,ˈadəˌpōz/ cells脂肪
• Adipose tissue also cushions vital organs and
insulates the body
• Cushion /ˈko͝oSHən/,
a pillow or pad stuffed with a mass of soft material, used as a
comfortable support for sitting or leaning on.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Phospholipids
•
In a phospholipid /ˌfäsfōˈlipid/, two fatty acids and a phosphate group
are attached to glycerol . 磷脂
•
The two fatty acid tails are hydrophobic, but the phosphate group and
its attachments form a hydrophilic head
•
Phosphate:/ˈfäsfāt/a salt or ester of phosphoric acid, containing PO43− or a
related anion or a group such as —OPO(OH)2. 磷酸盐
•
Hydrophobic:/ˌhīdrəˈfōbik/ 1. of or suffering from hydrophobia;2. tending to
repel or fail to mix with water.
•
Hydrophilic:/ˌhīdrəˈfilik/ having a tendency to mix with, dissolve in, or be
wetted by water, 亲水的
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Hydrophobic tails
Hydrophilic head
Fig. 5-13
(a) Structural formula
Choline
Phosphate
Glycerol
Fatty acids
Hydrophilic
head
Hydrophobic
tails
(b) Space-filling model
(c) Phospholipid symbol
Hydrophobic tails
Hydrophilic head
Fig. 5-13ab
(a) Structural formula
Choline
Phosphate
Glycerol
Fatty acids
(b) Space-filling model
•
When phospholipids are added to water, they self-assemble into a
bilayer, with the hydrophobic tails pointing toward the interior
•
The structure of phospholipids results in a bilayer arrangement found in
cell membranes
•
Phospholipids are the major component of all cell membranes
•
Bilayer /ˈbīˌlāər/, a film two molecules thick (formed, e.g., by lipids), in which
each molecule is arranged with its hydrophobic end directed inward toward the
opposite side of the film and its hydrophilic end directed outward
•
.
Membranes, /ˈmemˌbrān/, a thin sheet of tissue or layer of cells acting as a
boundary, lining, or partition in an organism
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 5-14
Hydrophilic
head
Hydrophobic
tail
WATER
WATER
Steroids
•
Steroids /ˈsterˌoid,ˈstirˌoid/ 类固醇 are lipids characterized by a carbon
skeleton consisting of four fused rings
•
Cholesterol /kəˈlestəˌrôl,kəˈlestəˌrōl/, an important steroid, is a
component in animal cell membranes. A compound of the sterol type
found in most body tissues. Cholesterol and its derivatives are important
constituents of cell membranes and precursors of other steroid compounds,
but a high proportion in the blood of low-density lipoprotein (which transports
cholesterol to the tissues) is associated with an increased risk of coronary
heart disease
•
Although cholesterol is essential in animals, high levels in the blood
may contribute to cardiovascular disease
•
Derivative, /dəˈrivədiv/, something that is based on another source
•
Lipoprotein, /ˈlipəˌprōtēn/, 脂蛋白, any of a group of soluble proteins that combine with and transport fat or other lipids
in the blood plasma.
•
Cholesterol /kəˈlestəˌrôl,kəˈlestəˌrōl/, 胆固醇, a compound of the sterol type found in most body tissues
•
Coronary /ˈkôrəˌnerē,ˈkärəˌnerē/, relating to or denoting the arteries which surround and supply the heart, 花冠的
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 5-15
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