26 Lipids.ppt 4i4v4u

Lipids

Chapter 26 26-1

Lipids  Lipids:

A heterogeneous class of naturally occurring organic compounds classified together on the basis of common solubility properties. • They are insoluble in water but soluble in aprotic organic solvents, including diethyl ether, methylene chloride, and acetone.

 Lipids

include:

• triglycerides, phospholipids, prostaglandins, prostacyclins, and fat-soluble vitamins. • cholesterol, steroid hormones, and bile acids.

26-2

Triglycerides  Triglyceride:

An ester of glycerol with three fatty

acids. Saponification O O CH2 OCR R'COCH O CH2 OCR'' A triglyceride

1 . NaOH, H2 O 2 . HCl, H2 O

CH2 OH HOCH CH2 OH

RCOOH +

1,2,3-Prop anetriol (Glycerol, glycerin)

R'COOH R''COOH Fatty acids

26-3

Fatty Acids  Fatty

acid: A carboxylic acid derived from hydrolysis of animal fats, vegetable oils, or membrane phospholipids. • Nearly all have an even number of carbon atoms, most between 12 and 20, in an unbranched chain. • The three most abundant are palmitic (16:0), stearic (18:0), and oleic acid (18:1), where the first number is the number of carbons and the second is the number of double bonds in the hydrocarbon chain. • In most unsaturated fatty acids, the cis isomer predominates; the trans isomer is rare. • Unsaturated fatty acids have lower melting points than their saturated counterparts; the greater the degree of unsaturation, the lower the melting point. 26-4

Fatty Acids  The

most common fatty acids. Carbon Atoms: Common Double Bonds Name

Melting Point (°C)

Satur ated Fatty Acids

Higher mp

12:0 14:0 16:0 18:0 20:0

Lauric acid Myristic acid Palmitic acid Ste aric acid Arachidic acid

44 58 63 70 77

Uns aturated Fatty Acids

Lower mp

16:1 18:1 18:2 18:3 20:4

Palmitoleic acid Oleic acid Linole ic acid Linole nic acid Arachidonic acid

1 16 -5 -11 -49

26-5

Triglycerides  Physical

properties depend on the fatty acid components. • Melting point increases as the number of carbons in its hydrocarbon chains increases and as the number of double bonds decreases. • Oils: Triglycerides rich in unsaturated fatty acids are generally liquid at room. • Fats: Triglycerides rich in saturated fatty acids are generally semisolids or solids at room temperature.

26-6

Triglycerides • example: a triglyceride derived from one molecule each of palmitic acid, oleic acid, and stearic acid, the three most abundant fatty acids in the biological world. p almitate (16:0) O oleate (18:1) O CH2 OC(CH2 ) 1 4 CH3 stearate (18:0) CH3 ( CH2 ) 7 CH=CH(CH2 ) 7 COCH O CH2 OC(CH2 ) 1 6 CH3

26-7

Triglycerides  The

lower melting points of triglycerides rich in unsaturated fatty acids are related to differences in their three-dimensional shape. • Hydrocarbon chains of saturated fatty acids can lie parallel with strong dispersion forces between their chains; they pack into well-ordered, compact crystalline forms and melt above room temperature. • Because of the cis configuration of the double bonds in unsaturated fatty acids, their hydrocarbon chains have a less ordered structure and dispersion forces between them are weaker; these triglycerides have melting points below room temperature. 26-8

Soaps and Detergents  Natural

soaps are prepared by boiling lard or other animal fat with NaOH, in a reaction called saponification (Latin, sapo, soap). O O CH2 OCR saponification + 3 N aOH RCOCH O CH2 OCR A triglyce ride (a trie ste r of glycerol)

CH2 OH CHOH

+

CH2 OH 1,2,3-Propanetriol (Glyce rol; Glycerin)

O + 3 RCO N a Sodium s oaps

-

+

COO Na

26-9

Soaps and Detergents  Soaps

clean by acting as emulsifying agents:

• Their long hydrophobic hydrocarbon chains are insoluble in water and tend to cluster in such a way as to minimize their with water. • Their polar hydrophilic carboxylate groups, on the other hand, tend to remain in with the surrounding water molecules. • Driven by these two forces, soap molecules spontaneously cluster into micelles.

26-10

Soaps and Detergents • A soap micelle: nonpolar (hydrophobic) hydrocarbon chains cluster in the inside and polar (hydrophilic) carboxylate groups lie on the surface.

26-11

Soaps and Detergents • micelle: A spherical arrangement of organic molecules in water clustered so that their hydrophobic parts are buried inside the sphere and their hydrophilic parts are on the surface of the sphere and in with water. • when soap is mixed with water-insoluble grease, oil, and fats, the nonpolar parts of the soap micelles “dissolve” these nonpolar dirt molecules and they are carried away in the polar wash water.

26-12

Soaps and Detergents  Soaps

form water-insoluble salts when used in water containing Ca(II), Mg(II), and Fe(III) ions (hard water). -

2 CH3 ( CH2 ) 1 4 COO Na

+

+

Ca

2+

A s odium soap (s oluble in water as micelles) -

2+

[ CH3 ( CH2 ) 1 4 COO ] 2 Ca Calciu m salt of a fatty acid (insoluble in water)

+

2 Na

+

26-13

Synthetic Detergents  The

design criteria for a good detergent are:

• a long hydrocarbon tail of 12 to 20 carbons. • a polar head group that does not form insoluble salts with Ca(II), Mg(II), or Fe(III) ions.  The

most widely used synthetic detergents are the linear alkylbenzenesulfonates (LAS).

26-14

Synthetic Detergents 1 . H2 SO 4 2 . Na OH

CH 3 ( CH2 ) 1 0 CH 2 Dodecylbenzen e

CH 3 ( CH2 ) 1 0 CH 2

SO 3

-

Na

+

Sodium 4-dode cylbenze nesulfon ate (an an ionic detergent)  Also

added to detergent preparations are:

• foam stabilizers. • bleaches. • optical brighteners. 26-15

Prostaglandins  Prostaglandins:

A family of compounds that have the 20-carbon skeleton of prostanoic acid. 9

5

7 6

8

1

3 2

4

COOH

10 11

12 13

14

15

16

18 17

19

20

Prostan oic acid

26-16

Prostaglandins, origin  Prostaglandins

are not stored in tissues as such, but are synthesized from membrane-bound 20carbon polyunsaturated fatty acids in response to specific physiological triggers. • One such polyunsaturated fatty acid is arachidonic acid (notice the all cis configurations). 9

8

11 12

6

14

5

COOH

15

Arachidonic acid

26-17

Prostaglandins, examples • Among the prostaglandins synthesized biochemically from arachidonic acid are: O 9

COOH

PGE2 11

15

HO HO H HO 9

PGF2

COOH 11

15

HO HO H

PGE2 generated in macrophages of the liver and lungs triggers the earliest phase of fever following any infection 26-18

Prostaglandins  Research

on the involvement of PGs in reproductive physiology has produced several clinically useful derivatives. • (15S)-15-methyl-PGF2 is used as a therapeutic abortifacient. extra methyl group at carb on -15

HO 9

COOH 11

HO

15

HO CH3 (15S)-15-Methyl-PGF2

26-19

Prostaglandins • The PGE1 analog, misoprostol, is used to prevent the ulceration associated with the use of aspirin. O COOH PGE 1 15

HO

16

HO H

O COOCH 3

Misopros tol HO HO

15

CH3

16

26-20

Eicosanoids  The

prostaglandins are of an even larger family of compounds called eicosanoids, all of which contain 20 carbons and are derived from polyunsaturated fatty acids. 1 5

HOOC 9

6 8

COOH

O 11

O

O

1 15

12 13

14

OH Th romboxane A2 (a potent vasoconstrictor)

20

H

7 9 8

H

14

20

15

11 13

OH OH Prostacyclin (a p latelet aggregation inhib itor)

26-21

Eicosanoids  Leukotrienes

are found primarily in white blood

cells. • One function is constriction of smooth muscles, especially those of the lungs. HO 11

9

1

7

20

6

COOH

5

S

O

COOH

glycine

14

L-cysteine Leu k otriene C 4 (LTC 4) (a smooth mus cle constrictor)

N H

HN

COOH N H2

L-glutamic acid

O

26-22

Steroids  Steroids:

A group of plant and animal lipids that have this tetracyclic ring structure. C A

D

B

 The

features common to the ring system of most naturally occurring steroids are illustrated next.

26-23

Steroids • The fusion of rings is trans and each atom or group at a ring junction is axial. • The pattern of atoms or groups along the ring junctions is nearly always trans-anti-trans-anti-trans. • The steroid system is nearly flat and quite rigid. • Most have have axial methyl groups at C-10 and C-13.

CH3

H

H

CH3

H H

26-24

Cholesterol

H3 C H3 C

H H

H

HO

26-25

Androgens  Androgens

- male sex hormones.

H3 C H3 C

OH H

H H

O

H3 C H3 C

H

O

H H

H

HO Tes tos terone

Androste rone

26-26

Synthetic Anabolic Steroids • A way to increase the testosterone concentration is to use a prohormone, which the body converts to testosterone; for example “andro”. H3 CHO CH 3 H3 C

H O

Meth androstenolon e

H

H3 C H3 C

H

N and rolon e decan oate

H

Meth enolone

O OC(CH2 ) 8 CH3

CH3

H

H

O

H H

O

OH

H

CH3

H

H3 C

O

H3 C

H H

O

H3 C

H

4-An dros tene-3,17-dione (an dro)

26-27

Available on the internet, dangerous 



Generic Name: methandrostenolone Danabol / Dianabol has always been one of the most popular anabolic steroids available. Danabol / Dianabol's popularity stems from it's almost immediate and very strong anabolic effects. 4-5 tablets a day is enough to give almost anybody dramatic results. It is usually stacked with deca durabolin and testosterone enanthate. Along with strong anabolic effects comes the usual androgen side effects, s often report an overall sense of well being. Danabol / Dianabol is a strong anabolic and androgenic product. It most often produced dramatic gains in size and strength. Danabol / Dianabol was also shown to increase endurance and glycogen retention. The down side is that this drug is responsible for a number of side effects. It is an alpha alkylated 17 compound, which is quite toxic to the liver. Average dosages for Danabol / Dianabol have been in the range of 15mg to 30mg a day oral or 50mg to 100mg a week by injection. Regarded by many athletes as being one of the most effective oral steroids ever produced. It was not known as the "Breakfast of Champions" for nothing. Danabol / Dianabol is still one of the most effective strength and size building oral steroids probably second only to Anadrol 50 but it is not as harsh on the system as Anadrol 50 is.

26-28

Estrogens  Estrogens

- female sex hormones. CH3

H3 C

H3 C C= O H

H3 C

H

H

H

H

H

O

O

H

HO Progesteron e H3 C H3 C

Estrone OH H

H H

O

H3 C H3 C

H

O

H H

H

HO Tes tos terone

Androste rone

26-29

Synthetic Estrogens  Progesterone-like

analogs are used in oral

contraceptives. "Nor" refers to the abs ence of a methyl group here. The methyl group is pres ent in ethin drone

HO C CH H3 C H

H H

H

O Norethindrone

26-30

Glucorticoid Hormones • • • •

Synthesized in the adrenal cortex. Regulate metabolism of carbohydrates. Decrease inflammation. Involved in the reaction to stress. CH2 OH H3 C

O H3 C

C= O OH

H H

O

CH2 OH H3 C

HO H3 C

H

C= O OH

H H

H

O Cortis one

Cortis ol

26-31

Mineralocorticoid Hormones • Synthesized in the adrenal cortex. • Regulate blood pressure and volume by stimulating the kidneys to absorb Na+, Cl-, and HCO3-. OH O H3 C

CH

CH2 OH C=O

H H

H

O Aldosterone

26-32

Bile Acids  Synthesized

in the liver, stored in the gallbladder, and secreted into the intestine where their function is emulsify dietary fats and aid in their absorption and digestion. OH

COOH

H H HO H

H OH

26-33

Biosynthesis of Steroids  The

building block from which all carbon atoms of steroids are derived is the two carbon acetyl group of acetyl-CoA Stage 1: synthesis of isopentenyl pyrophosphate from three molecules of acetyl-CoA. Stage 2: synthesis of cholesterol. Stage 3: conversion of cholesterol to other steroids.

choles terol

bile acids (e.g., cholic acid) se x hormones (e .g., te stos terone and estrone ) mineralocorticoid hormones (e .g., aldosterone) glucocorticoid hormon es (e.g., cortis one)

26-34

Vitamin E OH

Four isoprene units, ed head-to-tail, beginning here and ending at the aromatic ring

O Vitamin E (-Tocophe rol)

26-35

Phospholipids  Phospholipids

are the second most abundant group of naturally occurring lipids. • They are found almost exclusively in plant and animal membranes, which typically consist of 40% -50% phospholipids and 50% - 60% proteins. • The most abundant phospholipids are esters of phosphatidic acid (glycerol esterified with two molecules of fatty acid and one of phosphoric acid). • The three most abundant fatty acids in phosphatidic acids are palmitic acid (16:0), stearic acid (18:0), and oleic acid (18:1).

26-36

Phosphatidic acids, an example A

phosphatidic acid

• Further esterification with a low-molecular weight alcohol gives a phospholipid. 26-37

Phospholipids • Among the most common of these low-molecularweight alcohols are:

26-38

Phospholipids, an example A

lecithin

In aqueous solution, phospholipids spontaneously form into a lipid bilayer, with a back-to-back arrangement of lipid monolayers. 26-39

Biological Membranes  Fluid

mosaic model: A biological membrane consists of a phospholipid bilayer with proteins, carbohydrates, and other lipids embedded on the surface and in the bilayer. • fluid: Signifies that the protein components of membranes “float” in the bilayer and can move freely along the plane of the membrane. • mosaic: Signifies that the various components of the membrane exist side by side, as discrete units rather than combining to form new molecules and ions.

26-40

Biological Membranes • Fluid-mosaic model of a biological membrane showing the lipid bilayer and membrane proteins on the inner and outer surfaces of the membrane and penetrating the thickness of the membrane.

26-41

Fat-Soluble Vitamins  Vitamins

are divided into two broad classes on the basis of their solubility: • Those that are fat soluble, and hence classified as lipids. • Those that are water soluble.

 The

fat-soluble vitamins include A, D, E, and K.

26-42

Vitamin A • Occurs only in the animal world. • Found in the plant world in the form of a provitamin in a group of pigments called carotenes.

26-43

Vitamin A  The

best understood role of Vitamin A is its participation in the visual cycle in rod cells. • the active molecule is retinal (vitamin A aldehyde), which forms an imine with an -NH2 group of the protein opsin to form the visual pigment called rhodopsin. • the primary chemical event of vision in rod cells is absorption of light by rhodopsin followed by isomerization of the 11-cis double bond to the 11-trans configuration.

26-44

Vitamin A and the Chemistry of Vision

26-45

Vitamin D A

group of structurally related compounds that play a role in the regulation of calcium and phosphorus metabolism. • The most abundant form in the circulatory system is vitamin D3.

26-47

Vitamin E  Vitamin

E is a group of compounds of similar structure, the most active of which is tocopherol.

• In the body, vitamin E functions as an antioxidant; it traps peroxy radicals of the type HOO• and ROO• formed as a result of oxidation by O2 of unsaturated hydrocarbon chains in membrane phospholipids. 26-48

Vitamin K  The

name of this vitamin comes from the German word Koagulation, signifying its important role in the blood-clotting process.

26-49