LipidsLipids

Broadly defined as naturally occurring non-polar compounds having simple functional groups.

Major Categories of LipidsMajor Categories of Lipids

Fats and Oils

• Biosynthesis of fatty acids Phospholipids Waxes Terpenes Steroids Prostaglandins

FatsFats

Esters of fatty (long chain carboxylic) acids Common are triacyl glycerols, which can be

hydrolyzed (saponified) into soaps:

CH2O2C

CHO2C

CH2O2C

NaOHaq.

CH2OH

CHOH

CH2OH

+ C13H27CO2 C15H31CO2 C17H35CO2Na Na Na+ +

Soap (mixture of salts of fatty acids):

O

CH2OC

CHOC

CH2OCO

O

Micelles: mode of action of soap

P

P

P

P

P

P

PP

P

P

P

P

P

P

P

P

P

PP

P

P

P

P

P

Na O

O

P

Soap (above) can be represented as:

Soap (and detergents) form spherical clusters(right) called micelles; micelles surroundand dissolve non-polar substances (oily stains) and render them “soluble.”

OilOil

HH22OO

HH22OO

HH22OO

HH22OOHH22OO

HH22OO

Oils (polyunsaturated fats)Oils (polyunsaturated fats)

CH2OC

O

CHO

CH2OC

CO

O

Presence of cis double bonds in oils makes it difficultfor the molecules to pack regularly in a solid structure; oils have lower melting points than fats, and are liquids at RT.

Biosynthesis of Fatty AcidsBiosynthesis of Fatty Acids

Repetitive applications of thio-Claisen

reactions; explains why most fatty acids

have an even number of carbon atoms

Enolization / Carboxylation of Acetyl Coenzyme AEnolization / Carboxylation of Acetyl Coenzyme A

CH2=CSCoA

OHC

O

OH+

(acetyl CoA, a 2 C unit) (enol form)

CH3CSCoA

O

CH2=CSCoA

OH

HOCCH2CSCoA

OO

(malonyl CoA)

Acylation of Malonyl Coenzyme A with 2 Carbon unitAcylation of Malonyl Coenzyme A with 2 Carbon unit

HOCCH2CSCoA

OO

HOCCH=CSCoA

OH

O

CH3C S synthase

O

(malonyl CoA)

CH3CCHCSCoA

O O

COHO

Enol form

Decarboxylation, Reduction, Dehydration and ReductionDecarboxylation, Reduction, Dehydration and Reduction

-CO2CH3CCH2CSCoA

O O

[H] (NADPH)

-H2O

CH3CHCH2CSCoA

OH O

CH3CH=CHCSCoA

O [H]

(NADPH)

CH3CH2CH2CSCoA

O

(a 4 Carbon unit)

CH3CCHCSCoA

O O

COHO

Acylation of Malonyl Co A with 4 carbon unitAcylation of Malonyl Co A with 4 carbon unit

HOCCH2CSCoA

OO

HOCCH=CSCoA

OH

O

CH3CH2CH2C S synthase

O

(malonyl CoA)

CH3CH2CH2CCHCSCoA

O O

COHO

(4 carbon unit)

Conversion to 6 carbon unitConversion to 6 carbon unit

CH3CH2CH2CCHCSCoA

O O

COHO

decarboxylation,reduction of C=Odehydrationreduction of C=C

CH3CH2CH2CH2CH2CSCoA

O

(6 carbon unit)

Acylation of Malonyl Co A with 6 carbon unitAcylation of Malonyl Co A with 6 carbon unit

CH3CH2CH2CH2CH2C

O

S synthase

CH3CH2CH2CH2CH2CCHCSCoA

O O

COHO

(malonyl CoA)

HOCCH=CSCoA

OH

O

HOCCH2CSCoA

OO (6 carbon unit)

Conversion to 8 carbon unit...etc.Conversion to 8 carbon unit...etc.

CH3CH2CH2CH2CH2CH2CH2CSCoA

O

reduction of C=Odehydration,reduction of C=C

decarboxylation,

CH3CH2CH2CH2CH2CCHCSCoA

O O

COHO

(8 carbon unit)

Common Saturated Fatty AcidsCommon Saturated Fatty Acids

CO2H

CO2H

CO2H

C14 Myristic Acid

C16 Palmitic Acid

C18 Stearic Acid

Common Unsaturated Fatty Acids

C

O

OH

Palmitoleic

C

O

OH

Oleic

Linoleic

C

O

OH

Polyunsaturated Fatty Acids

Polyunsaturated fatty acids (PUFAs) include those having two and three double bonds.

Omega-3 fatty acids are those unsaturated fatty acids that have a double bond between the third and fourth carbon from the end of the carbon chain (opposite the CO2H group).

A common omega-3 fatty acid found in fish oil is linolenic acid:

Omega-3 fatty acids are considered beneficial for brain function.

C

O

OH

1

2

3 6 9

Composition of Fats and Oils

lauric myristic palmitic stearic oleic linoleic

C12 C14 C16 C18 C18(1) C18(2)

Animal FatsLard - 1 25 8 50 10Beef Fat - - 27 14 50 3Butter Fat 2 10 29 10 27 5Human Fat 1 3 25 8 46 10Whale Blubber - 8 12 3 35 10

Vegetable OilsCoconut oil 48 18 11 2 7 1Corn oil - 1 10 3 45 35Olive oil - 1 7 3 82 6Peanut oil - - 7 5 58 24Soybean oil - - 10 2 29 51

Fats and Oils in Nuts

Nut g. prot./oz. g. fat/oz % sat’d % MUFAs % PUFAs

Walnuts 4 18 10 15 75

Almonds 6 14 10 65 25

Hazelnuts 4 17 9 77 14

Cashews 4 13 21 62 17

Macadamia 2 22 16 76 8

Pecans 3 20 9 53 28

Peanuts 7 14 16 52 32

Phospholipids

Phospholipids are long-chain fatty esters of glycerol also containing a phosphoric acid derivative.

They contain a glycerol backbone, like fats and oils, but they have a phosphate group with an ionic alkyl ammonium group also attached.

Representative Phospholipids

CH2O

CO H

CH2O P

O

O

O CH2CH2N(CH3)3

C R

O

C

O

R'

CH2O

CO H

CH2O P

O

O

O CH2CH2NH3

C R

O

C

O

R'

Phosphatidylcholine (lecithin)

Phosphatidylethanolamine (cephalin)

CH2

CO H

CH2O P

O

O

O CH2CH2N(CH3)3

C

OOC

O

Phospholipids…

P

Can be represented as:

CH2

CO H

CH2O P

O

O

O CH2CH2N(CH3)3

C

OOC

O

Lipid Bilayer of Cell Membranes

P P P P P P P

P P P P P P P

Cell membrane

Outside the cell (aqueous)

Inside the cell (aqueous)

WaxesWaxes

Long chain esters of long chain fatty acids

CH3(CH2)mCO2(CH2)nCH3

m = 8 - 18 n = 15 - 35

Waxes:

O

O

(present in beeswax)

TerpenesTerpenes

Derived biosynthetically from a branched five carbon unit, isopentenyl pyrophosphate:

OP

OP

O

OO

O O

isopentyl pyrophosphate isopreneisopentenyl pyrophosphate

Terpenes...Terpenes...

Common monoterpenes (C10):

OH

geraniol

CH2OH

CHO

citral

OH

menthol

Some more common terpenes

zingiberene (ginger)a sesquiterpene; 15 Cs

limonene(lemons)

citronellal(oil of citronella)

O

H

O

H

SteroidsSteroids

Involved in regulatory processes and in sexual characteristics and functions

Common steroids include cholesterol, estradiol, testosterone, estrone and progesterone

CH3

CH3

R

CH3

CH3

R

AA BB

CC DD

AA BBCC

DD

Some Common Steroids

CH3

CH3

H

HH

O

HOH

CH3

CH3

H

HH

HO

O

CH3

H

HH

HO

O

testosterone androsterone

estrone

H

HH

HO

OHCH3

estradiol

…More Common Steroids

H

CH3

H

HH

O

C CHOH

progesterone

CH3

CH3

H

HH

O

CO CH3

norethrindroneethynylestradiol

CH3

H

HH

HO

C CHOH

CH3

CH3

H

HH

HO

H

cholesterol

…More Common Steroids

CH3

CH3

H

HH

O

O OHC

O CH2OH

cortisone

CH3

CH3

H

HH

HO

H

CO2H

HOH

OH

cholic acid

Prostaglandins

C20 carboxylic acids that contain a 5-member ring and have two long side chains.

They were first isolated from prostate glands of sheep, but now they are known to have widespread distribution among tissues, and to exhibit an extraordinarily wide range of biological effects.

Representative Structures

Biosynthetic source: Biosynthetic source: arachidonic acidarachidonic acid

Prostaglandin E1 (PGE1) Prostaglandin F2 (PGF2)

CO2H

CO2H

HO H

H

HHO

O

CO2H

HO H

H

HHO

HO H

Some Varied Biological Effects of Prostaglandins

Lower blood pressure Affect clotting of blood Lower gastric secretions Promote inflammation (countered by aspirin,

which inhibits PG biosynthesis) Affect reproductive systems Stimulate uterine contractions during childbirth

Final ExamFinal Exam

Review:

A review session is scheduled for class on Monday, April 30 in DO 202. Bring questions, and bring the last 4 sheets of the Course-Pack.

Final Exam:

Monday, May 7, 8:00 am – 11:00 am

(Dobo Hall, Room 202)