1 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.

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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 8.1: Fatty AcidsAcids

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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: Waxes8.2: Waxes Waxes are esters produced by combining fatty acids with long chain alcohols.

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Animal fats and vegetable oils are triglycerides or triacylglycerides, in which three fatty acid residues are joined to glycerol by ester bonds.

fatty acid

Glycerol

structure of a triglyceride

fatty acid

fatty acid

8.3: Triglycerides8.3: Triglycerides

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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

• Phospholipids get their name from the fact that phosphate anion (PO4

3-) is one of the components used in their formation.

• There are two classes of phospholipids.– Glycerophospholipids (contains glycerol)– Sphingolipids (contain sphingosine)

8.4: Phospholipids and Glycolipids

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• Glycerophopholipids are made by combining glycerol, two fatty acids, one phosphate group, and one amino alcohol molecule.

fatty acidGlycerol

structure of a glycerophosphoplipid

fatty acidphosphate alcohol

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CH3(CH2)7 CH CH (CH2)7C

O

O CH2

CHOC

O

CH3(CH2)14CH2O P

O-

O

O

CH2CH2NH3+

(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 acidsphingosine

structure of a sphingolipid

phosphate alcohol

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CH2O P

O-

O

O

CH2CH2N

CH3

CH3

CH3

(This group is usually: choline)

C

H

OHCH3(CH2)12 CH CH

C

OCHNH

CH3(CH2)5CH CH(CH2)7 +

Sphingolipid: (This is a spingomyelin)

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• Glycolipids are lipids that contain a sugar residue. In many cases this residue is attached to a sphingosine backbone.

fatty acidsphingosine

structure of a glycolipid

sugar

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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).

Example:

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Purpose of phospholipids: Formation of cell membrane.

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• 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

8.5: Steroids8.5: Steroids

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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Cholesterol

Progesterone

Cortisol(glucocorticoid:regulate uptakecarbohydrates)

Aldosterone(mineralocorticoid: regulate level of minerals)

Testosterone (Androgens)

estradiol (estrogens)

Bile salts (taurocholate, glycocholate; help in thedigestion of lipids)

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:

Norgestrel Ethinyl estradiol

Birth control Pills

-Prevent ovulation.-Cause changes on the uterus wall.

Variety of Steroid compounds:

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• 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.

8.6: Eicosanoids

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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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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?

Exercise:

Strategy:

Consider the effect of cis double bonds on membrane fluidity.