Transcript Chapter 20: Carboxylic Acids and Nitriles

Chapter 27.
Biomolecules: 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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27.1 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

Tri-esters of glycerol with three longchain carboxylic acids, fatty acids.
4
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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5
Unsaturated and Polyunsaturated
Fatty Acids

Oleic (C18 with one C=C) and linolenic (C18 with 3 C=C)
are the most abundant unsaturated
6
27.2 Soap

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


“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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27.3 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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27.4 Prostaglandins & Other Eicosanoids
C20 lipids that
contain a fivemembered ring
with two long side
chains
 Present in small
amounts in all
body tissues and
fluids
 Many physiological
effects

14
Prostaglandin Sources

Biosynthesized from arachidonic acid (C20
unsaturated fatty acid)
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27.5 Terpenoids
Steam distillation of plant extracts produces “essential
oils”
 Chemically related to compounds in turpentine (from pine
sap) called terpenes and thus called terpenoids
 Mostly hydrocarbons (some oxygens) that do not contain
esters (stable to hydrolysis)

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Biosynthesis of Terpenoids
Isopentenyl pyrophosphate (IPP) forms higher
isoprenoids in reactions catalyzed by prenyl transferase
 Monoterpenoids, diterpenoids, and tetraterpoids arise
from 1-deoxyxylulose 5-phosphate (DXP).
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Mevalonate Pathway to
Isopentenyl Diphosphate
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Begins with the conversion of acetate to acetyl CoA
followed by Claisen condensation to yield acetoacetyl
CoA
Catalyzed by acetoacetyl-CoA acetyltransferase
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Aldol Condensation
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Carbonyl condensation reaction of acetoacetyl CoA with acetyl CoA
Produces 3-hydroxy-3-methylglutaryl CoA (HMG-CoA)
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Reduction
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
HMG CoA is reduced to mevalonate
Catalyzed by HMG CoA reductase utilizing NADPH
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Phosphorylation & Decarboxylation
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Pyrophosphorylation gives mevalonyl-PP
Addition of phosphate from ATP followed by loss of CO2
and phosphate
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Conversion of Isopentenyl Diphosphate
to Terpenoids

For triterpenes and
larger, head-to-head
coupling of farnesyl
diphosphates gives
squalene
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Mechanism of Isomerization

Isomerization of IPP to DMAPP is catalyzed by IPP
isomerase through a carbocation pathway
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Coupling Mechanism

Nucleophilic substitution reaction in which the double
bond of IPP behaves as a nucleophile in displacing
diphosphate ion leaving group (PPO)
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Conversions of Monoterpenoids

Typically involves carbocation intermediates and multistep
reaction pathways catalyzed by a terpene cyclase
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27.6 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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Male Sex Hormones
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Testosterone and androsterone are the two most
important male sex hormones, or androgens
Androstanedione is a precursor
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Female Sex Hormones
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Estrone and estradiol are the two most important female
sex hormones, or estrogens
Progesterone is the most important progestin, steroids
that function in pregnancy
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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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27.7 Steroid Biosynthesis
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Enzyme-catalyzed
addition of
oxygen atom to
squalene
Stereospecific
formation of an
oxirane from an
alkene
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Which fatty acid is not commonly found in
nature?
20%
1.
x
2.
x
3.
x
4.
None of these is
commonly found in nature.
All of these are commonly
found in nature.
5.
1
20%
2
20%
20%
3
4
20%
5
Which of the following would not be
classified as a lipid?
20%
1.
1
2.
2
3.
3
4.
All of these are lipids.
None of these are lipids.
5.
1
20%
2
20%
20%
3
4
20%
5
Which of the following describes how a soap cleans?
1.
The fatty acids react with grease
molecules to form water soluble
compounds that are subsequently
washed away.
2.
The fatty acids form micelles which
encapsulate grease molecules. These
micelles are soluble in water and
consequently washed away.
3.
The fatty acids react with grease
molecules to generate new compounds
that can form micelles in water. These
micelles are soluble in water and
consequently washed away.
4.
All of these statements accurately
describe how soap works.
5.
None of these statements accurately
describe how soap works.
20%
1
20%
2
20%
20%
3
4
20%
5
The following molecule would be
expected to form micelles.
50%
1.
2.
50%
True
False
1
2
What forces are responsible for lipid bilayer
and micelle formation?
20%
1.
2.
3.
4.
5.
20%
20%
20%
3
4
20%
covalent bonding and
electrostatic interactions
hydrophobic effects and
hydrogen bonding
electrostatic interactions
and hydrophobic effects
electrostatic interactions
and fluid mosaics
hydrophobic effects and
fluid mosaics
1
2
5
The figure shown is:
20%
1.
2.
3.
4.
5.
phosphatidylethanolamine
phosphatidylcholine
phosphatidylserine
sphingosine
sphingomyelin
1
20%
2
20%
20%
3
4
20%
5
What do these two lipids have in common?
20%
1.
2.
3.
4.
5.
20%
20%
20%
3
4
20%
They are eicosanoids.
They form micelles in
water.
They are prostaglandins.
They are steroids.
They are used as
detergents.
1
2
5
Which is a role of the prostaglandins?
1.
2.
3.
4.
5.
They stimulate the
contraction of uterine
muscle.
They lower blood
pressure in the blood
stream.
They suppress gastric
ulceration.
All of these
None of these
20%
1
20%
2
20%
20%
3
4
20%
5
The molecule shown below is a:
20%
1.
2.
3.
4.
5.
20%
20%
20%
3
4
20%
thromboxane
prostaglandin
leukotriene
eicosanoid
thromboxane and
eicosanoid
1
2
5
The molecule shown below is:
20%
1.
2.
3.
4.
5.
20%
20%
20%
3
4
20%
lanosterol
camphor
β-carotene
patchouli alcohol
None of these
1
2
5
The first step of mevalonate synthesis,
shown below, is a:
The 1st step of mevalonate synthesis, shown is a:
20%
1.
2.
3.
4.
5.
20%
20%
20%
3
4
20%
Claisen condensation
aldol-like condensation
reduction reaction
substitution reaction
Schiff base formation
1
2
5
Why can the molecule below not be classified as a
steroid?
20%
1.
2.
3.
4.
5.
20%
20%
20%
3
4
20%
Steroids cannot have double
bonds.
Steroids cannot contain
branched hydrocarbon chains.
Steroids have a different
arrangement of rings.
Steroids are usually comprised
of benzene rings, making them
mostly flat.
All of these
1
2
5
How is cholesterol transported through the
blood stream?
20%
1.
2.
3.
4.
5.
20%
20%
20%
3
4
20%
through micelles
through ion channels
by prostaglandins
by lipoproteins
as water solvated ions
1
2
5
In which organ of the body is cholesterol
synthesized?
20%
1.
2.
3.
4.
5.
20%
20%
20%
3
4
20%
the lungs
the gallbladder
the liver
the kidneys
the pancreas
1
2
5
Which of the following is not a good
indicator of health?
20%
1.
2.
3.
4.
5.
20%
20%
20%
3
4
20%
cholesterol levels below
200 mg/dL
LDL levels greater than
100 mg/dL
HDL levels greater than
60 mg/dL
active, athletic lifestyle
diets rich in seafood
1
2
5