Download Chapter 25 Lipids - Inver Hills Community College

Organic Chemistry, 6th Edition
L. G. Wade, Jr.
Chapter 25
Lipids
Jo Blackburn
Richland College, Dallas, TX
Dallas County Community College District
2006, Prentice Hall
Introduction
• Classified by solubility, not structure.
• Can be extracted from cells by nonpolar
organic solvents.
• Complex lipids are easily hydrolyzed.
Waxes
Triglycerides
• Simple lipids are not easily hydrolyzed.
Steroids
Prostaglandins
Terpenes
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2
Examples of Lipids
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3
Waxes
• Esters of long-chain fatty acids with
long-chain alcohols.
• Spermaceti is found in the head of the
sperm whale and is probably used to
control buoyancy.
• Most natural waxes are protective coats
for plants’ leaves, insects’ exoskeletons,
mammals’ fur, and birds’ feathers. =>
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4
Triglycerides
• Fatty acid esters of glycerol.
• Fats
Solid at room temperature
Most are derived from mammals
• Oils
Liquid at room temperature
Most are derived from plants or coldblooded animals.
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5
Fatty Acids
• Unbranched carboxylic acids with
12-20 carbons.
• Most contain an even number of
carbons because they are built from
acetic acid units.
• Melting points increase with increasing
molecular weights.
• Unsaturation greatly lowers the melting
point.
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Melting Points
• A cis double bond bends the molecule
so it cannot pack efficiently.
• A trans double bond has less effect.
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Fats and Oils
• Most fats have saturated fatty acids.
• Most oils have unsaturated fatty acids.
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8
Saponification
• “Soap-making”
• Base-catalyzed hydrolysis of ester
linkages in fats and oils.
CH2 OH
O
CH2 O C
O
(CH2)16CH3
CH O C
O
(CH2)16CH3
CH2 O C
CH OH
CH2 OH
+ 3 NaOH
O
+-
+ 3 Na O C
(CH2)16CH3
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A soap
(CH2)16CH3
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Soap Structure
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Grease in Soap Solution
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Detergents
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Phospholipids
• Contain a phosphate ester bond.
• Phosphoglycerides usually have one
phosphoric acid group and two fatty acids.
• The phosphate may have an additional
alcohol attached by an ester linkage.
O
CH2 O C
O
(CH2)14CH3
CH O C
O
(CH2)14CH3
+
CH2 O P O CH2CH2NH3
O_
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13
Lipid Bilayer
Cell membranes are a bilayer of
phosphoglycerides
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18
12 CH3
Steroids
2
3
17
11
19
CH3 C 13
D 16
1
14
9
8
15
10
H
A
B
5
7
4 H 6
• Polycyclic, usually all trans.
• Common structural features:
=O or -OH at C3
Side chain at C17
Double bond from C5 to either C4 or C6.
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A-B Ring Junction
May be cis, but usually is trans.
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Cholesterol
CH3
CH3
3
HO
5
H
17
H
H
H
6
H
• Common biological intermediate.
• Probably a precursor to other steroids.
• Side chain at C17 and double bond C5-C6.
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Sex Hormones
CH3
CH3
H
OH
H
CH3
H
OH
H
H
H
O
H
H
HO
testosterone
estradiol
• Female hormone has an aromatic ring
and one less methyl group than the
male hormone.
• Testosterone is converted to estradiol in
the ovaries.
=> 18
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Prostaglandins
• Biochemical regulators more powerful
than steroids.
• Regulate functions such as:
Blood pressure
Blood clotting
Allergic response
Digestive activity
Labor onset
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Structure of Prostaglandins
• Cyclopentane ring with two long side
chains trans to each other.
• Most have 20 carbon atoms.
• Derived from arachidonic acid.
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Terpenes
•
•
•
•
•
Composed of 5-carbon isopentyl groups.
Isolated from plants’ essential oils.
C:H ratio of 5:8, or close to that.
Pleasant taste or fragrant aroma.
Examples:
Anise oil
Bay leaves
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Structure of Terpenes
Two or more isoprene units, 2-methyl-1,3butadiene with some modification of the
double bonds.
myrcene, from
bay leaves
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Classification
• Terpenes are classified by the number of
carbons they contain, in groups of 10.
• A monoterpene has 10 C’s, 2 isoprenes.
• A diterpene has 20 C’s, 4 isoprenes.
• A sesquiterpene has 15 C’s, 3 isoprenes.
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Terpenoids
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End of Chapter 25
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