Download Chapter 20: Carboxylic Acids and Nitriles

Lipids
Why this Chapter?
Lipids are the largest and most diverse class of
biomolecules
To examine lipid structure, function, and metabolism
About Lipids
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Natural materials that preferentially extract into nonpolar
organic solvents
Includes fats, oils, waxes, some vitamins and hormones,
some components of membrane
General types: esters (“saponifiable”) and those that can’t
be hydrolyzed
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Waxes, Fats, and Oils
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Waxes - contain esters formed from long-chain (C16C36) carboxylic acids and long-chain alcohols (C24-C36)
Triacontyl hexadecanoate is in beeswax
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Triacylglycerol
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Tri-esters of glycerol with three longchain carboxylic acids, fatty acids.
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Fatty Acids (from Fats and Oils)
Straight-chain (C12 - C20) carboxylic acids
 Double bonds are cis-substituted but trans-fatty acids also
occur
 A fat or oil in nature occurs as a mixture of many different
triacylglycerols
 The most abundant saturated fatty acids are palmitic (C16)
and stearic (C18)
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Unsaturated and Polyunsaturated
Fatty Acids
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Oleic (C18 with one C=C) and linolenic (C18 with 3 C=C)
are the most abundant unsaturated
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Soap
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A mixture of sodium or potassium salts of long-chain fatty
acids produced by alkaline hydrolysis (saponification) of
animal fat with alkali
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Cleansing Action of Soap
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The carboxylate end of the long-chain molecule is ionic
and therefore is preferentially dissolved in water
The hydrocarbon tail is nonpolar and dissolves in grease
and oil
Soaps enable grease to be dissolved into water
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Detergents
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“Hard” water contains Mg+2 and Ca+2 that form insoluble
salts with soaps
Synthetic detergents are alkylbenzene sulfonates that
dissolve dirt like soaps but do not form scums with Mg+2
and Ca+2 .
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Phospholipids
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Phospholipids are diesters of H3PO4, phosphoric acid
Phosphoric acid can form monoesters, diesters and
triesters
In general these are known as “phosphates”
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Phosphoglycerides
Contain a glycerol backbone linked by ester bonds to two
fatty acids and phosphoric acid
 Fatty acid residues with C12–C20
 The phosphate group at C3 has an ester link to an amino
alcohol
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Sphingolipids
The other major group of phospholipids
 Sphingosine or a dihydroxyamine backbone
 Constituents of plant and animal cell membranes
 Abundant in brain and nerve tissue, as coating around
nerve fibers.
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Phosphoglyceride Membranes
Phosphoglycerides comprise the major lipid component of
cell membranes
 Nonpolar tails aggregate in the center of a bilayer
 Ionic head is exposed to solvent
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Steroids
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Steroids,are another class of nonsaponifiable lipid, defined
by structure
Has four fused rings A, B, C, and D, beginning at the lower
left
Carbon atoms are numbered beginning in the A ring
The six-membered rings are in fixed chair conformations
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Functions of Steroids
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In humans as hormones, steroids are chemical messengers
secreted by glands and carried through the bloodstream
to target tissues
Also widely distributed as cholesterol
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Adrenocortical Hormones
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Adrenocortical steroids: secreted by the adrenal glands
near the upper end of each kidney
Mineralocorticoids: control tissue swelling by regulating
cellular salt balance
Glucocorticoids: regulation of glucose metabolism and in
the control of inflammation
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Synthetic Steroids
Made in pharmaceutical laboratories as new drugs
 Includes oral contraceptives and anabolic agents
 Methandrostenolone is an anabolic steroid used for
tissue-building
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