Chapter 8: Outline

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Chapter 8 Outline
8.1 Fatty Acids 8.2 Waxes 8.3 Triglycerides (or
triacylglyceries) 8.4 Phospholipids and
Glycolipids 8.5 Steroids
8.6 Eicosanoids 8.7 Membranes
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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
structure of a triglyceride
Glycerol
fatty acid
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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Phospholipids
8.4 Phospholipids and Glycolipids

• 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.

Glycerol
fatty acid
fatty acid
phosphate
alcohol
structure of a glycerophosphoplipid
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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.

sphingosine
fatty acid
phosphate
alcohol
structure of a sphingolipid
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• Glycolipids are lipids that contain a sugar
  residue. In many cases this residue is attached
  to a sphingosine backbone.

sphingosine
fatty acid
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
  cholesterol-containing deposits in arteries.

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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

• 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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Anabolic Steroids
Variety of Steroid compounds
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.