Transcript Hein and Arena - University of Wisconsin–Eau Claire

Chapter 8: Outline
8.1 Fatty Acids
8.6 Eicosanoids
8.2 Waxes
8.7 Membranes
8.3 Triglycerides (or
triacylglyceries)
8.4 Phospholipids and
Glycolipids
8.5 Steroids
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• Fatty acids are carboxylic acids that typically contain between 12 and 20
carbon atoms.
• Fatty acids typically have an even number of carbon atoms, because they
are built from two-carbon molecules. Some examples are:
8.1: Fatty
Acids
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Fatty acids differ from one another in the number of
carbon atoms that they contain and in their number of
carbon-carbon double bonds.
saturated fatty acids have only single bonds.
monounsaturated fatty acids have one double bond.
polyunsaturated fatty acids have two or more double
bonds.
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Fatty acid reacting with base:
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8.2: Waxes
Waxes are esters produced by combining fatty acids
with long chain alcohols.
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8.3: Triglycerides
Animal fats and vegetable oils are triglycerides or
triacylglycerides, in which three fatty acid residues are
joined to glycerol by ester bonds.
fatty acid
fatty acid
structure of a triglyceride
Glycerol
fatty acid
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What is Olestra?
(The ester bonds are
not hydrolyzed
when heated.)
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• Fats are solids at room temperature
because they contain more saturated
fatty acid residues and have melting
points above room temperature.
• Vegetable oils, on the other hand, are
liquids at room temperature because
they contain a high percentage of
unsaturated fatty acid residues and
have melting points below room
temperature.
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• One of the primary biological roles of
triglyceride is to provide energy.
• On a gram-per-gram basis,
triglycerides can provide more than
twice as many calories (energy) as do
carbohydrates and proteins.
• In animals these molecules are stored
in adipose tissue (fat cells) for
subsequent use.
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Important Reactions of Triglycerides
• Catalytic hydrogenation (or reduction)
– (similar to: alkene + H2/Pt  alkane)
• Saponification
– Hydrolysis of ester groups on the triglyceride in
the presence of hydroxide (-OH)
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Partial Hydrogenation of fatty acyl group:
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Saponification rxn is the same as hydrolysis of ester group:
Which bond is broken at the ester
functional group?
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8.4: Phospholipids and Glycolipids
Phospholipids
• Phospholipids get their name from the
fact that phosphate anion (PO43-) is one
of the components used in their
formation.
• There are two classes of phospholipids.
– Glycerophospholipids (contains glycerol)
– Sphingolipids (contain sphingosine)
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• Glycerophopholipids are made by
combining glycerol, two fatty acids,
one phosphate group, and one amino
alcohol molecule.
fatty acid
fatty acid
Glycerol
phosphate alcohol
structure of a glycerophosphoplipid
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O
CH3(CH2)7
CH CH
(CH2)7C O CH2
O
O CH
O
CH3(CH2)14 C
CH2O P O CH2CH2NH3+
O(This group is usually: ethanolamine,
choline, serine)
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• Sphingolipids contain the alcohol
sphingosine, and sphingolipids that belong
to the phospholipid family contain
phosphate attached to both sphingosine and
an alcohol residue.
fatty acid
sphingosine
phosphate alcohol
structure of a sphingolipid
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Sphingolipid: (This is a spingomyelin)
H
CH3(CH2)12
CH CH C OH
O
NH CH
O
CH3
C
CH3(CH2)5CH CH(CH2)7
+
CH2O P O CH2CH2N CH3
O-
CH3
(This group is usually: choline)
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• Glycolipids are lipids that contain a sugar
residue. In many cases this residue is
attached to a sphingosine backbone.
fatty acid
sphingosine
sugar
structure of a glycolipid
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Example:
How many products would be obtained when the
phosphatidylethanolamine below is saponified?
Hint: Each of the ester bonds in the molecule is
hydrolyzed (or broken).
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Purpose of phospholipids:
Formation of cell membrane.
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8.5: Steroids
•
Steroids are a class of lipids that share the same basic
ring structure - three fused 6-carbon atom rings and one
5-carbon atom ring.
•
There are three important types of steroids:
– cholesterol
– steroid hormones
– bile salts
The steroid nucleus
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Cholesterol
• Cholesterol is the steroid found most often in
humans and other animals.
• Regardless of what you eat, your body will
contain some cholesterol, because it is
manufactured in the liver.
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Cholesterol
• In cholesterol, the nonpolar rings and hydrocarbon
chain are hydrophobic and the -OH group, which
makes up a much smaller part of the molecule, is
hydrophilic.
• Overall, this makes the molecule amphipathic.
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LDLs and HDLs
• The major function of low density lipoproteins
(LDLs) is to transport cholesterol and
phospholipids from the liver to the cells, where
they are incorporated into membranes or, in the
case of cholesterol, transformed into other
steroids.
• High density lipoproteins (HDLs) transport
cholesterol and phospholipids from the cells back
to the liver.
• Low HDL and high LDL levels in the blood are warning
signs of atherosclerosis, the buildup of cholesterol29
containing deposits in arteries.
Steroid Hormones
• Hormones, molecules that regulate the
function of organs and tissues, come in
a variety of forms.
– Some, such as sex hormones and
adrenocorticoid hormones, are steroids.
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Steroid Hormones
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• The manufacture of the steroid hormones
begins with cholesterol.
• Shortening of the hydrocarbon chain and
alterations on the ring converts cholesterol
into progesterone and other sex hormones.
• Progesterone is used to make other sex
hormones and the adrenocorticoid
hormones.
• Adrenocorticoid hormones are produced in
the adrenal glands, starting from
progesterone.
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Another role of Cholesterol:
Cholesterol
Bile salts (taurocholate, glycocholate; help in the
digestion of lipids)
Progesterone
Testosterone (Androgens)
Cortisol
(glucocorticoid:
regulate uptake
carbohydrates)
Aldosterone
(mineralocorticoid:
regulate level of minerals)
estradiol (estrogens)
• Bile salts, produced from cholesterol, are amphipathic.
• Glycocholate, taurocholate, and other bile salts are released
from the gallbladder into the small intestine, where they aid
digestion by forming emulsions with dietary lipids.
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Variety of Steroid compounds:
Anabolic Steroids:
Birth control Pills
Norgestrel
Ethinyl estradiol
-Prevent ovulation.
-Cause changes on the uterus wall.
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8.6: Eicosanoids
• The lipids called eicosanoids are hormones
that are derived from arachidonic acid, a
polyunsaturated fatty acid containing 20
carbons (the prefix eicosa means 20).
• When hydrolyzed from a certain
phospholipid by hormone action,
arachidonic acid undergoes reactions that
transform it into the various eicosanoids prostaglandins, thromboxanes, and
leukotrienes.
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Prostaglandins
• Prostaglandins have a wide range of biological effects:
– causing pain, inflammation, fever, affecting blood
pressure, inducing labor (PGE2)
Thromboxanes and Leukotrienes
• Thromboxanes, such as thromboxane A2, are
involved in blood clotting.
• Leukotrienes, including leukotriene A4, induce
muscle contractions in the lungs and are linked to
asthma attacks. Some anti-asthma drugs block the
production of leukotrienes.
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Nonsteroidal Anti-inflammatory Drugs (NSAIDs)
• NSAIDs such as aspirin, acetaminophen, and ibuprofen
reduce pain, fever, and inflammation by blocking the
action of an enzyme involved in the conversion of
arachidonic acid into prostaglandins and thromboxanes.
These are the enzymes: COX-1 and COX-2
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8.7: Membranes
•Membranes - barriers that surround cells or that
separate one part of a cell from another, are a
bilayer of amphipathic lipids - usually
phospholipids, glycolipids, and cholesterol.
•The lipids are arranged so that their hydrophilic
heads interact with one another and with water at
the surface of the membrane, and their hydrophobic
tails interact with one another at the center of the
membrane.
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Fluid mosaic model of cell membrane:
What are these molecules?
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Transport across cell membrane:
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Exercise:
Plant cell membranes contain a higher proportion of
unsaturated fatty acid residues than do animal
membranes. Which type of membrane would you
expect to be more fluid, plant or animal?
Strategy:
Consider the effect of cis double bonds on
membrane fluidity.
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