15 CH110 Lipids Timberlake

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Chapter 15 Lipids

15.1

Lipids

Copyright © 2007 by Pearson Education, Inc.

Publishing as Benjamin Cummings



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Lipids

Lipids are

Biomolecules that contain fatty acids or a steroid

nucleus.

Soluble in organic solvents but not in water. Named for the Greek word lipos, which means ―fat.‖

Extracted from cells using organic solvents.



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Types of Lipids

The types of lipids containing fatty acids are

Waxes.

Fats and oils (triacylglycerols).

Glycerophospholipids.

Prostaglandins.

Not steroids, as they do not contain fatty acids.



4

Structures of Lipids





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15.2 Fatty Acids





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Fatty Acids

Fatty acids

Are long-chain

carboxylic acids.

Typically contain 12-18carbon atoms.

Are insoluble in water.

Can be saturated or

unsaturated.





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Fatty Acid Formulas

The formulas for fatty acids are written as

Condensed formulas.

Line-bond formulas.

For example caprylic acid with 8 carbon atoms.

CH3—(CH2)6—COOH

CH3—CH2—CH2—CH2—CH2—CH2—CH2—COOH

OH

O



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Saturated fatty acids have

Single C –C bonds.

Molecules that fit closely together

in a regular pattern. Strong attractions between fatty

acid chains.

High melting points that make

them solids at room temperature.

Saturated Fatty Acids

Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings



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Some Saturated Fatty Acids




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Unsaturated Fatty Acids

Unsaturated fatty acids

Have one or more double C=C bond

Typically contain cis double bonds.




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Properties of Unsaturated Fatty

Acids

Unsaturated fatty acids

Have ―kinks‖ in the fattyacid chains.

Do not pack closely.

Have few attractionsbetween chains.

Have low melting points.

Are liquids at roomtemperature.

―kinks‖ in

chain





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Comparing Melting Points

of

Some Fatty Acids




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Learning Check

Assign the melting points of –17°C, 13°C, and 69°C

to the correct fatty acid. Explain.

stearic acid (18 C) saturated

oleic acid (18 C) one double bondlinoleic acid (18 C) two double bonds



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Solution

Stearic acid is saturated and would have a higher

melting point than the unsaturated fatty acids.

Because linoleic has two double bonds, it would have

a lower mp than oleic acid, which has one double

bond.

stearic acid mp 69°C saturated

oleic acid mp 13°C

linoleic acid mp -17°C most unsaturated



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Prostaglandins

Prostaglandins have

20 carbon atoms in their fatty acid chains.

An OH on carbon 11 and 15.

A trans double bond at carbon 13.


C 11

C 15C 13



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Prostaglandins in the Body

Prostaglandins are

Produced by injuredtissues.

Involved in pain,fever, andinflammation.

Not produced whenanti-inflammatory

drugs such as aspirininhibit their synthesis.





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Omega-6 and Omega 3- Fatty

Acids

Fatty acids

In vegetable oils are mostly omega-6 with

the first C=C at C6.

linoleic acid

CH3 ─(CH2)4 ─CH=CH─CH2 ─CH=CH─(CH2)7 ─COOH

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In fish oils are mostly omega-3 with the

first C=C at C3.

linolenic acidCH3 ─CH2 ─(CH=CH─CH2)3 ─(CH2)6 ─COOH

3

Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings



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Some Omega-6 and Omega-3

Fatty Acids



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Learning Check

Write a fatty acid with 10 carbon atoms that is:

A. saturated

B. monounsaturated omega-3

C. monounsaturated omega-6



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Solution

Write a fatty acid with 10 carbon atoms that is:

A. saturated

CH3—CH

2—CH

2—CH

2—CH

2—CH

2—CH

2—CH

2—CH

2—COOH

B. monounsaturated omega-3

CH3—CH2—CH=CH—CH2—CH2—CH2—CH2—CH2—COOH

C. monounsaturated omega-6

CH3—CH2—CH2—CH2—CH2—CH=CH—CH2—CH2—COOH



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Waxes, Fats, and Oils





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Waxes

Waxes are

Esters of saturated fatty acids and long-chain alcohols.

Coatings that prevent loss of water by leaves of plants.

TABLE 17.2




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Fats and Oils: Triacylglycerols

Fats and oils are

Also called triacylglycerols.

Esters of glycerol.

Produced by esterification. Formed when the hydroxyl

groups of glycerol react with the

carboxyl groups of fatty acids.





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In a triacylglycerol,

Glycerol forms ester bonds with three fatty acids.

Triacylglycerols




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Formation of a Triacylglycerol

glycerol + three fatty acids triacylglycerol

OHCH2

OH

OHCH2

CHO

(CH2)14CH3CHO

O

(CH2)14CH3CHO

O

(CH2)14CH3CHO

+ 3H2O

O

O

C (CH2)14CH3

CH O

O

C (CH2)14CH3

CH2 O

O

C (CH2)14CH3

CH2

+



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Olive Oil

Olive oil

Contains a high

percentage of oleic

acid, which is a

monounsaturated fatty

acid with one cis

double bond.




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Learning Check

What are the fatty acids in the following triacylglycerol?

(CH2)12CH3

O

C

CH(CH2)7CH3(CH2)7CH

O

C

O

(CH2)16CH3C

O

O

OCH2

CH2

CH



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Solution

Stearic acid

Oleic acid

Myristic acid(CH2)12CH3

O

C

CH(CH2)7CH3(CH2)7CH

O

C

O

(CH2)16CH3C

O

O

OCH2

CH2

CH



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Melting Points of Fats and Oils

A triacylglycerol that is a fat

Is solid at room temperature.

Is prevalent in meats, whole milk, butter, and cheese.

A triacylglycerol that is an oil

Is liquid at room temperature.

Is prevalent in plants such as olive and safflower.



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Oils with Unsaturated Fatty Acids

Oils

Have more unsaturated fats.

Have cis double bonds that cause ―kinks‖ in the

fatty acid chains. Cannot pack triacylglycerol molecules as close

together as in fats.

Have lower melting points than saturated fats.

Are liquids at room temperature.



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Diagram of Triacylglycerol with


Unsaturated fatty acid

chains have kinks that

do not allow close

packing.




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Saturated and Unsaturated Fatty

Acids In Fats and Oils




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Chemical Properties of

Triacylglycerols





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The chemical reactions of triacylglycerols are similar

to those of alkenes and esters.

In hydrogenation, double bonds in unsaturated

fatty acids react with H2 in the presence of a Ni orPt catalyst.

In hydrolysis, ester bonds are split by water in the

presence of an acid, a base, or an enzyme.

Chemical Properties of

Triacylglycerols



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Hydrogenation of Oils

The hydrogenation of oils

Adds hydrogen (H2) to the carbon atoms of double bonds.

Converts double bonds to single bonds.

Increases the melting point.

Produces solids such as margarine and shortening.

Copyright © 2007 by Pearson Education, Inc Publishing as Benjamin Cummings



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Hydrogenation

Ni

+ 3H2

glyceryl tripalmitoleate

(tripalmitolean)

glyceryl tripalmitate

(tripalmitin)

O

(CH2)14CH3C

O

(CH2)14CH3C

O

(CH2)14CH3C

O

O

OCH2

CH2

CH

CH(CH2)7CH3(CH2)5CH

O

C

CH(CH2)7CH3(CH2)5CH

O

C

CH(CH2)7CH3(CH2)5CH

O

C

O

O

OCH2

CH2

CH



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What product(s) is obtained from the complete

hydrogenation of glyceryl trioleate?

1. Glycerol and 3 oleic acids2. Glyceryltristearate

3. Glycerol and 3 stearic acids

Learning Check



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What product(s) is obtained from the complete

hydrogenation of glyceryl trioleate?

2. Glyceryltristearate

Solution



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Olestra, A Fat Substitute

Olestra is

Used in foods as an artificial fat.

Sucrose linked by ester bonds to several long-chainfatty chains.

Not broken down in the intestinal tract.




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Cis and Trans Fatty Acids

Unsaturated fatty acids can be

Cis with bulky groups on same side of C=C.CH3 ─ (CH2)5 (CH2)7 ─ COOH cis

C=CH H

Trans have bulky groups on opposite sides of C=C.

CH3 ─ (CH2)5 H

C=C trans

H (CH2)7 ─ COOH



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Trans Fatty Acids and

Hydrogenation

Trans fatty acids

Are formed during hydrogenation when cis double

bonds are converted to trans double bonds.

In the body behave like saturated fatty acids. Are estimated to make up 2-4% of our total

Calories.

Are reported in several studies reported to raise

LDL-cholesterol and lower HDL-cholesterol.



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Learning Check

(1) True or (2) False

A. There are more unsaturated fats in vegetable oils.

B. Vegetable oils have higher melting points than fats.C. Hydrogenation of oils converts some cis-double

bonds to trans- double bonds.

D. Animal fats have more saturated fats.



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Solution

(1) True or (2) False

A. T There are more unsaturated fats in vegetable oils.

B. F Vegetable oils have higher melting points than fats.

C. T Hydrogenation of oils converts some cis-double

bonds to trans- double bonds.

D. T Animal fats have more saturated fats.



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Hydrolysis

In hydrolysis,

Triacylglycerols split into glycerol and three fatty acids.

An acid or enzyme catalyst is required.

OCH2

OCH

OCH2

OHCH2

OHCH

OHCH2

O

(CH2)14CH3CHO

H2O

O

(CH2)14CH3C

O

(CH2)14CH3C

O

(CH2)14CH3C

H+

+3

+ 3

15 CH110 Lipids Timberlake

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