Copyright © Houghton Mifflin Company. All rights reserved.3–13–1 15.1 Intro to Lipids Lipids...

Copyright © Houghton Mifflin Company. All rights reserved. 3–1

15.1 Intro to Lipids

Lipids are biochemical molecules that are insoluble or sparingly soluble in water, but are soluble in nonpolar organic solvents.

Uses of lipids:

Storage of energy

Insulation

Protection from mechanical damage

Major component of cell membranes


15.1 Intro to Lipids

Types of lipids:

I. Saponifiable lipids contain fatty acids bound as esters. Saponification (soap-making) is hydrolysis of the esters and frees the fatty acids. These lipids can be classified as polar or nonpolar.

II. Nonsaponifiable lipids do not contain fatty acids bound as esters.


15.2 Structures of Fatty Acids

Fatty acids are carboxylic acids with un-branched hydrocarbon chains. They contain an even number of carbon atoms.

Fatty acids can be

saturated: contain no double bonds

monunsaturated: contain one double bond

polyunsaturated: contain several double bonds


15.2 Structures of Fatty AcidsThe double bonds in naturally-occurring fatty

acids have cis double bonds. These put kinks in the hydrocarbon backbone.

Two of the polyunsaturated fatty acids are essential in the diet; they cannot be syn-thesized by the body. Both contain 18 carbon atoms. Fish and vegetable oils are dietary sources of these fatty acids.

Linoleic acid (2 double bonds)

Linolenic acid (3 double bonds)



Stearic acid

Oleic acid

Linoleic acid Linolenic acid



C

O

OH

C

O

OH

Stearic acid, a saturated fatty acid

Oleic acid, a monounsaturated fatty acid

C

O

OH

Linoleic acid, an Ω-6 polyunsaturated acid

C

O

OH

Linolenic acid, an Ω-3 polyunsaturated acid


15.3 Properties of Fatty Acids

The melting points of fatty acids depend on the num-ber of carbon atoms and the degree of unsaturation.



The bent shapes of unsaturated fatty acids pre-vent them from fitting together and forming high-melting solids.

Fatty acids with trans double bonds are found in “trans fats.” The trans double bonds are formed when vegetable oils are processed. These fatty acids have higher melting points than the cis isomers.



Melting points: 70C 13C 45C


15.4 TriglyceridesTriglycerides are triesters. They are products

of the reaction of glycerol and fatty acids. They are also called triacylglycerols, and are the nonpolar saponifiable lipids.


15.4 TriglyceridesSimple triglycerides contain three identical

fatty acids. Mixed triglycerides contain three different fatty acids.


15.4 Triglycerides

Triglycerides are the most abundant lipids, and are used for storage of energy.

Solid or semisolid triglycerides are called fats. They contain mainly saturated fatty acids. They are found in meats and tropical nuts.

Liquid triglycerides are called fats. They contain mainly unsaturated fatty acids. They are found in fish and plants.


15.4 Triglycerides

The kinks associated with unsaturated fatty acids prevent the molecules from packing neatly and forming solids.


15.4 Triglycerides

Fatty acid contents of common fats and oils.


15.5 Reactions of Triglycerides

Complete hydrolysis of triglycerides produces the triol, glycerol, and free fatty acids.

Metabolic hydrolysis requires enzymes from the pancreas. Usually, two of the fatty acids are hydrolyzed, leaving a monoglyceride.

Triglyceride + 3 H2O Glycerol + 3 Fatty Acids

Triglyceride + 2 H2OMonoglyceride+ 2 Fatty Acids


15.5 Reactions of TriglyceridesSaponification is hydrolysis of triglycerides in

basic solution. The fatty acid is obtained as its carboxylate salt, or soap.

The carboxylate anion has a polar end and a nonpolar hydrocarbon chain. The polar end is hydrophilic (water-loving) and the nonpo-lar chain is hydrophobic (water-fearing.)

Triglyceride + 3 OH1− Glycerol + 3 Carboxylates

CO

Opolar

"head"nonpolar "tail"


15.5 Reactions of TriglyceridesThe two parts of the molecules associate

to form micelles and other structures.

From Wikipedia


15.6 PhosphoglyceridesPhosphoglycerides are polar saponifiable

lipids. Two of the alcohols on glycerol are esterified with fatty acids. The third is esterified with phosphoric acid, which is esterified with an aminoalcohol.

CH

CH2

CH2

OC

O

R2

O C

O

R1

O P

O

O R3

O


15.6 Phosphoglycerides

Different types of phosphoglycerides contain different aminoalcohols.

Phosphatadylcholines, a.k.a. lecithins, contain choline

HO CH2 CH2 N

CH3

CH3

CH3

Cephalins contain ethanolamine or serine

HO CH2 CH2 N

H

H

H

HO CH2 CH N

H

H

H

COO


15.6 PhosphoglyceridesThe phosphate ester of lecithins is quite

polar. It has a charged phosphate group and a quaternary amine.



A space-filling drawing shows its polar head and two nonpolar tails.



Phosphatidylcholines form micelles and are good emulsifiers.

They are major components of cell membranes.

They are abundant in egg yolk and soybeans.



Cephalins are found in heart, liver, and brain tissue.

They are important in the clotting of blood.


15.7 Sphingolipids

Sphingolipids are polar saponifiable lipids based on sphingosine rather than glycerol.

A fatty acid is bonded to the nitrogen as an amide.

CH3 (CH2)12 CC CH

H

H

OH

CH NH2

CH2 OH


15.7 SphingolipidsSphingomyelins contain a phosphate ester

bonded to choline.

CH3 (CH2)12 CC CH

H

H

OH

CH NH

CH2

C

O

R

O

PO

O

O CH2 CH2 N

CH3

CH3

CH3


15.7 Sphingolipids

Sphingomyelins are found in cell membranes, and are important structural components of the myelin sheath of nerves.


15.7 SphingolipidsCerebrosides contain a monosaccharide

rather than a phosphate.

CH3 (CH2)12 CC CH

H

H

OH

CH NH

CH2

C

O

R

OO

OH

OH

OH

CH2OH

Galactose

Glycoside linkage


15.8 Steroids

Steroids are nonsaponifiable lipids that possess the steroid skeleton.

A B

C D


15.8 Steroids

Cholesterol is the most abundant steroid in the human body.

HO

CH3 H

CH3

HH

H3C

CH3

CH3


15.8 SteroidsCholesterol is the most abundant

steroid in the human body.

HO

CH3 H

CH3

HH

H3C

CH3

CH3

H


15.8 SteroidsCholesterol is the most

abundant steroid in the human body.


15.8 Steroids

Cholesterol, when mixed with a fat or oil, enables the substance to absorb a fair amount of water.

Cholesterol is abundant in wool fat, a.k.a. lanolin.

Cholesterol is used as a grease vehicle in ointments when water-soluble com-ponents are required.


15.8 Steroids

Cholesterol is a precursor to other important steroids

Bile salts

Hormones

Vitamin D

Cholesterol is a risk factor for atherosclerosis, a buildup of plaque, in the arteries.


15.8 SteroidsBile salts have a polar group at the end of the

hydrocarbon at carbon 17. They emulsify lipids in the digestive system.

HO

CH3 H

CH3

HH

H3C

HOH

H

O

NH

O O

sodium glycocholate


15.8 SteroidsHormones are messenger molecules

produced in ductless glands. They are carried to specific tissues where they trigger a response.

Steroid hormones regulate “sugar, salt, and sex!”

Adrenocortical steroids regulate sugar and salt. They are secreted by the adrenal glands. Some are used as anti-inflammatory drugs.


15.8 Steroids

Hormones are messenger molecules produced in ductless glands. They are carried


15.8 Steroids

Estrogens are steroid hormones that cause development of secondary sex characteristics in females and regulate the menstrual cycle.

Progestins are steroid hormones that regulate pregnancy.

Androgens promote development of secondary sex characteristics in males and promote muscle growth. They are sometimes called anabolic steroids.


15.8 Steroids

Estrogens are steroid hormones that cause development of secondary sex characteristics in females and regulate the menstrual cycle.

Progestins are steroid hormones that regulate pregnancy.

Androgens promote development of secondary sex characteristics in males and promote muscle growth.


15.8 Steroids

Many synthetic steroids are available as drugs. Anabolic steroids cause the body to increase protein synthesis, especially in the muscles. They also prevent the breakdown of muscle tissue and affect cell differentiation, favoring muscle over fat cells.

Side effects include acne, liver disease, infer-tility, and development of inappropriate sec-ondary sex characteristics. They can stunt growth in puberty and affect sex character-istics of unborn infants.


15.8 Steroids

Tamoxifen and raloxifene are selective estrogen receptor modulators, a.k.a. SERMs, that block estrogen receptors and slow or prevent growth of breast cancer.

ON

Tamoxifen (NolvadexTM)

ON

O

S

HO

HO

Raloxifene (EvistaTM)


15.8 Steroids

Diethylstilbestrol, a.k.a. DES, was used in 1940’s and 1950’s to prevent miscarriage.

It caused vaginal cancer in daughters of women who took it. (Rare)

It caused premature labor in daughters of women who took it. (Common)

OH

HO


Prostaglandins

Prostaglandins are lipids derived from arachidonic acid.

They were first isolated from prostate glands.

Prostaglandins have hormone-like prop-erties and are involved in inflammation.

Aspirin blocks production of prostaglandins.


Prostaglandins

Prostaglandins are lipids derived from arachidonic acid. They have hormone-like properties. They are involved in inflammation; aspirin blocks production of prostaglandins.

C

O

OHCH3

O

HO

CH3

OH

C

O

OH

arachidonic acid

PGF2α


15.9 Cell Membranes

Cell membranes separate the aqueous environment inside the cell from the external aqueous environment.

The membrane also controls movement of substances into and out of the cell.

Phospholipids are a major component of cell membranes. They form lipid bilayers.


15.9 Cell Membranes

The membrane also controls movement of substances into and out of the cell.

Phospholipids are a major component of cell membranes. They form lipid bilayers.


15.9 Cell MembranesThe kinks associated with cis double bonds

in fatty acid chains prevent tight packing of the lipid molecules in a lipid bilayer.


15.9 Cell MembranesCholesterol molecules fit between fatty acid

chains in a lipid bilayer. They regulate the rigidity of the structure.


15.9 Cell MembranesProteins are also components of the membrane.

They help move nutrients, and act as receptors for hormones and neurotransmitters.

Copyright © Houghton Mifflin Company. All rights reserved.3–13–1 15.1 Intro to Lipids Lipids...

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