chapter 25 lipids jo blackburn richland college, dallas, tx dallas county community college district...
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Chapter 25Lipids
Jo BlackburnRichland College, Dallas, TX
Dallas County Community College District2006,Prentice Hall
Organic Chemistry, 6th EditionL. G. Wade, Jr.
Chapter 25 2
Introduction• Classified by solubility, not structure.
• Can be extracted from cells by nonpolar organic solvents.
• Complex lipids are easily hydrolyzed.WaxesTriglycerides
• Simple lipids are not easily hydrolyzed.SteroidsProstaglandinsTerpenes =>
Chapter 25 4
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. =>
Chapter 25 5
Triglycerides
• Fatty acid esters of glycerol.• Fats
Solid at room temperatureMost are derived from mammals
• OilsLiquid at room temperatureMost are derived from plants or cold-
blooded animals. =>
Chapter 25 6
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. =>
Chapter 25 7
Melting Points
• A cis double bond bends the molecule so it cannot pack efficiently.
• A trans double bond has less effect.
=>
Chapter 25 8
Fats and Oils• Most fats have saturated fatty acids.
• Most oils have unsaturated fatty acids.
=>
Chapter 25 9
Saponification
• “Soap-making”
• Base-catalyzed hydrolysis of ester linkages in fats and oils.
CH O C
O
(CH2)16CH3
CH2 O C
O
(CH2)16CH3
CH2 O C
O
(CH2)16CH3
+ 3 NaOH
CH2
CH
CH2
OH
OH
OH
+ 3 Na+ -O C
O
(CH2)16CH3
A soap=>
Chapter 25 13
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.
CH O C
O
(CH2)14CH3
CH2 O P
O
CH2 O C
O
(CH2)14CH3
O
O CH2CH2NH3+
_ =>
Chapter 25 15
Steroids
• Polycyclic, usually all trans.• Common structural features:
=O or -OH at C3Side chain at C17Double bond from C5 to either C4 or C6.
=>
CH3
H
H
A B
C DCH31
2
34
56
7
8910
1112
13
1415
16
17
18
19
Chapter 25 17
Cholesterol
• Common biological intermediate.
• Probably a precursor to other steroids.
• Side chain at C17 and double bond C5-C6. =>
CH3
H
HOH
H
HHCH3
3 5 6
17
Chapter 25 18
Sex Hormones
• Female hormone has an aromatic ring and one less methyl group than the male hormone.
• Testosterone is converted to estradiol in the ovaries. =>
CH3
H
HO
H
HHOH
estradiol
CH3
H
O
H
HH
CH3
OH
testosterone
Chapter 25 19
Prostaglandins
• Biochemical regulators more powerful than steroids.
• Regulate functions such as:Blood pressureBlood clottingAllergic responseDigestive activityLabor onset
=>
Chapter 25 20
Structure of Prostaglandins• Cyclopentane ring with two long side
chains trans to each other.
• Most have 20 carbon atoms.
• Derived from arachidonic acid.
=>
Chapter 25 21
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 oilBay leaves =>
Chapter 25 22
Structure of Terpenes
Two or more isoprene units, 2-methyl-1,3-butadiene with some modification of the double bonds.
myrcene, frombay leaves
=>
Chapter 25 23
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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