LIPIDS By Henry Wormser, Ph.D. - PowerPoint Presentation

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LIPIDS

By Henry Wormser, Ph.D.

PSC 3110 – Fall semester 2008

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Introduction

Definition: water insoluble compounds

Most lipids are fatty acids or ester of fatty acidThey are soluble in non-polar solvents such as petroleum ether, benzene, chloroformFunctionsEnergy storage

Structure of cell membranes

Thermal blanket and cushion

Precursors of hormones (steroids and prostaglandins)

Types:

Fatty acids

Neutral lipids

Phospholipids and other lipids

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Fatty acids

Carboxylic acid derivatives of long chain hydrocarbons

Nomenclature (somewhat confusing)Stearate – stearic acid – C18:0 – n-octadecanoic acid

General structure:

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Fatty acids

Common fatty acids n = 4 butyric acid (butanoic acid)

n = 6 caproic acid (hexanoic acid) n = 8 caprylic acid (octanoic acid) n = 10 capric acid (decanoic acid)

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Fatty acids

common FA’s: n = 12: lauric acid (n-dodecanoic acid; C12:0

)n = 14: myristic acid (n-tetradecanoic acid; C14:0)n = 16: palmitic acid (n-hexadecanoic acid; C16:0

)

n = 18; stearic acid (n-octadecanoic acid; C

18:0

)

n = 20; arachidic (eicosanoic acid; C

20:0

)

n= 22; behenic acid

n = 24; lignoceric acid

n = 26; cerotic acid

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Less common fatty acids

iso – isobutyric acid

anteisoodd carbon fatty acid – propionic acidhydroxy fatty acids – ricinoleic acid, dihydroxystearic acid, cerebronic acidcyclic fatty acids – hydnocarpic, chaulmoogric acid

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PHYTANIC ACID

A plant derived fatty acid with 16 carbons and branches at C 3, C7, C11 and

C15. Present in dairy products and ruminant fats.

A peroxisome responsible for the metabolism of phytanic acid is defective

in some individuals. This leads to a disease called Refsum’s disease

Refsum’s disease is characterized by peripheral polyneuropathy, cerebellar

ataxia and retinitis pigmentosa

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Less common fatty acids

These are alkyne fatty acids

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Fatty acids

Fatty acids can be classified either as:saturated or unsaturated

according to chain length:short chain FA: 2-4 carbon atomsmedium chain FA: 6 –10 carbon atomslong chain FA: 12 – 26 carbon atoms

essential fatty acids vs those that can be biosynthesized in the body:

linoleic and linolenic are two examples of essential fatty acid

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Unsaturated fatty acids

Monoenoic acid (monounsaturated)

Double bond is always

cis

in natural fatty acids.

This lowers the melting

point due to “kink” in

the chain

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Unsaturated fatty acids

Dienoic acid: linoleic acid

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Unsaturated fatty acids

Various conventions are in use for indicating the number and position of the double bond(s)

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Unsaturated fatty acids

Polyenoic acid (polyunsaturated)

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Unsaturated fatty acids

Monoenoic acids (one double bond):16:1, 9 w7: palmitoleic acid (

cis-9-hexadecenoic acid18:1, 9 w9: oleic acid (cis-9-octadecenoic acid)

18:1, 9

w

9: elaidic acid (

trans

-9-octadecenoic acid)

22:1, 13

w

9: erucic acid (

cis

-13-docosenoic acid)

24:1, 15

w

9: nervonic acid (

cis

-15-tetracosenoic acid)

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Unsaturated fatty acids

Trienoic acids (3 double bonds)18:3;6,9,12 w6 :

g-linolenic acid (all cis-6,9,12-octadecatrienoic acid)18:3; 9,12,15 w3 :

a

-linolenic acid (all-

cis

-9,12,15-octadecatrienoic acid)

Tetraenoic acids (4 double bonds)

20:4; 5,8,11,14

w

6: arachidonic acid (all-

cis

-5,8,11,14-eicosatetraenoic acid)

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Unsaturated fatty acids

Pentaenoic acid (5 double bonds)

20:5; 5,8,11,14,17 w3: timnodonic acid or EPA (all-cis-5,8,11,14,17-eicosapentaenoic acid)*

Hexaenoic acid (6 double bonds)

22:6; 4,7,10,13,16,19

w

3: cervonic acid or DHA (all-cis-4,7,10,13,16,19-docosahexaenoic acid)*

Both FAs are found in cold water fish oils

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Typical fish oil supplements

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Properties of fats and oils

fats are solids or semi solidsoils are liquids

melting points and boiling points are not usually sharp (most fats/oils are mixtures)when shaken with water, oils tend to emulsifypure fats and oils are colorless and odorless (color and odor is always a result of contaminants) – i.e. butter (bacteria give flavor, carotene gives color)

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Examples of oils

Olive oil – from Oleo europa (olive tree)

Corn oil – from Zea maysPeanut oil – from Arachis hypogaeaCottonseed oil – from

Gossypium

Sesame oil – from

Sesamum indicum

Linseed oil – from

Linum usitatissimum

Sunflower seed oil – from

Helianthus annuus

Rapeseed oil – from

Brassica rapa

Coconut oil – from

Cocos nucifera

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Non-drying, semi-drying and drying oils

based on the ease of autoxidation and polymerization of oils (important in paints and varnishes)

the more unsaturation in the oil, the more likely the “drying” processNon-drying oils:Castor, olive, peanut, rapeseed oils

Semi-drying oils

Corn, sesame, cottonseed oils

Drying oils

Soybean, sunflower, hemp, linseed, tung, oiticica oils

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Fatty acid reactions

salt formationester formationlipid peroxidation

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Soaps

Process of formation is known as saponification

Types of soaps:Sodium soap – ordinary hard soapPotassium soap – soft soap (shaving soaps are potassium soaps of coconut and palm oils)Castile soap – sodium soap of olive oilGreen soap – mixture of sodium and potassium linseed oil

Transparent soap – contains sucrose

Floating soap – contains air

Calcium and magnesium soaps are very poorly water soluble (hard water contains calcium and magnesium salts –these insolubilize soaps)

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Lipid peroxidation

a non-enzymatic reaction catalyzed by oxygenmay occur in tissues or in foods (spoilage)

the hydroperoxide formed is very reactive and leads to the formation of free radicals which oxidize protein and/or DNA (causes aging and cancer)principle is also used in drying oils (linseed, tung, walnut) to form hard films

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Hydrogenated fats

hydrogenation leads to either saturated fats and or trans fatty acidsthe purpose of hydrogenation is to make the oil/fat more stable to oxygen and temperature variation (increase shelf life)

example of hydrogenated fats: Crisco, margarine

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Neutral lipids

Glycerides (fats and oils) ;glyceridesGlycerolEster of glycerol -

mono glycerides, diglycerides and triglyceridesWaxes – simple esters of long chain alcohols

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GLYCERIDES

Function: storage of energy in compact form and cushioning

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Stereospecific numbering

carbon 2 of triglycerides is frequently asymmetric since C-1 and C-3 may be substituted with different acyl groupsby convention we normally draw the hydroxyl group at C-2 to the left and use the designation of sn2 for that particular substituent

C-1 and C-3 of the glycerol molecule become sn1 and sn3 respectively

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Analytical methods to evaluate lipids

saponification numberiodine value (Hanus method)free fatty acidsacetyl number

Reichert-Meissl numberHPLC/GC (for more precise analysis)

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Saponification number

gives some clue as to the average size of fatty acids in a given sample of fatdefined as the number of milligrams of KOH needed to neutralize the fatty acids in 1 Gm of fat

butter (large proportion of short chain FAs) sap. no. 220 – 230oleomargarine (long chain FAs) sap. No is 195 or less

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Iodine number

measures the degree of unsaturation in a given amount of fat or oil

the iodine number is the number of grams of iodine absorbed by 100 grams of fatCottonseed oil: 103 –111Olive oil: 79 – 88Linseed oil: 175 –202frequently used to determine adulteration of commercial lots of oils

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Acetyl number

some fatty acids have hydroxyl groups

The acetyl number gives the proportion of these hydroxyl-containing fatty

acids in a given sample of fat or oil

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Acetyl number

the acetyl number is the number of milligrams of KOH needed to neutralize the acetic acid of 1 Gm of acetylated fatexamples:

castor oil – 146 –150cod liver oil – 1.1cottonseed oil – 21 – 25olive oil – 10.5

peanut oil – 3.5

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Reichert – Meissl number

measures the amount of volatile fatty acids (low MW and water soluble Fas)the R-M number is the number of milliliters of 0.1N alkali required to neutralize the soluble fatty acids distilled from 5 Gm of fat

butter fat has a high R-M number

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WAXES

simple esters of fatty acids (usually saturated with long chain monohydric alcohols)

Beeswax

– also includes some free alcohol and fatty acids

Spermaceti

– contains cetyl palmitate (from whale oil) –useful for

Pharmaceuticals (creams/ointments; tableting and granulation)

Carnauba wax

– from a palm tree from brazil – a hard wax used on

cars and boats

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Bee’s wax

Spermaceti source

Carnauba wax source

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Waxes

Examples of long chain monohydric alcohols found in waxes

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Phospholipids

the major components of cell membranesphosphoglycerides

Phospholipids are generally composed of FAs, a nitrogenous base, phosphoric

acid and either glycerol, inositol or sphingosine

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Phosphatidyl inositol

Commonly utilized in cellular signaling

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Sphingolipids

Based on sphingosine instead of glycerol

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Sphingomyelin (a ceramide)

It is a ubiquitous component of animal cell membranes, where it is by far the most abundant sphingolipid. It can comprise as much as 50% of the lipids in certain tissues, though it is usually lower in concentration than phosphatidylcholine

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Ether glycerophospholipids

Possess an ether linkage instead of an acyl group at the C-1 position of glycerolPAF ( platelet activating factor)

A potent mediator in inflammation, allergic response and in shock (also responsible for asthma-like symptomThe ether linkage is stable in either acid or basePlasmalogens: cis

a

,

b

-unsaturated ethers

The alpha/beta unsaturated ether can be hydrolyzed more easily

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Ether glycerophospholipids

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glycolipids

There are different types of glycolipids: cerebrosides, gangliosides,

lactosylceramides

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GLYCOLIPIDS

CerebrosidesOne sugar molecule

Galactocerebroside – in neuronal membranesGlucocerebrosides – elsewhere in the bodySulfatides or sulfogalactocerebrosides

A sulfuric acid ester of galactocerebroside

Globosides: ceramide oligosaccharides

Lactosylceramide

2 sugars ( eg. lactose)

Gangliosides

Have a more complex oligosaccharide attached

Biological functions: cell-cell recognition; receptors for hormones

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Gangliosides

complex glycosphingolipids that consist of a ceramide backbone with 3 or more sugars esterified,one of these being a sialic acid such as N-acetylneuraminic acidcommon gangliosides: GM1

, GM2, GM3, GD1a, GD1b, G

T1a

, GT

1b

, G

q1b

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Ganglioside nomenclature

letter G refers to the name gangliosidethe subscripts M, D, T and Q indicate mono-, di-, tri, and quatra(tetra)-sialic-containing gangliosidesthe numerical subscripts 1, 2, and 3 designate the carbohydrate sequence attached to ceramide

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Ganglioside nomenclature

Numerical subscripts:1. Gal-GalNAc-Gal-Glc-ceramide2. GalNAc-Gal-Glc-ceramide3. Gal-Glc-ceramide

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A ganglioside (G

M1

)

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Cardiolipids

A polyglycerol phospholipid; makes up 15% of total lipid-phosphorus

content of the myocardium – associated with the cell membrane

Cardiolipids are antigenic and as such are used in serologic test for

syphilis (Wasserman test)

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Sulfolipids

also called sulfatides or cerebroside sulfatescontained in brain lipidssulfate esters of cerebrosidespresent in low levels in liver, lung, kidney, spleen, skeletal muscle and heart

function is not established

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Lipid storage diseases

also known as sphingolipidoses

genetically acquireddue to the deficiency or absence of a catabolic enzymeexamples:Tay Sachs disease

Gaucher’s disease

Niemann-Pick disease

Fabry’s disease

http://www.ninds.nih.gov/disorders/lipid_storage_diseases/lipid_storage_diseases.htm

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Genetic defects in ganglioside metabolism

leads to a buildup of gangliosides (ganglioside GM2) in nerve cells, killing them

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Tay-Sachs disease

a fatal disease which is due to the deficiency of hexosaminidase A activity

accumulation of ganglioside GM2 in the brain of infantsmental retardation, blindness, inability to swallowa “cherry red “ spot develops on the macula (back of the the eyes)

Tay-Sachs children usually die by age 5 and often sooner

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Genetic defects in globoside metabolism

Fabry’s disease:Accumulation of ceramide trihexoside in kidneys of patients who are deficient in lysosomal

a-galactosidase A sometimes referred to as ceramide trihexosidaseSkin rash, kidney failure, pains in the lower extremitiesNow treated with enzyme replacement therapy: agalsidase beta (Fabrazyme)

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Genetic defects in cerebroside metabolism

Krabbe’s disease: Also known as globoid leukodystrophy

Increased amount of galactocerebroside in the white matter of the brainCaused by a deficiency in the lysosomal enzyme galactocerebrosidaseGaucher’s disease:

Caused by a deficiency of lysosomal glucocerebrosidase

Increase content of glucocerebroside in the spleen and liver

Erosion of long bones and pelvis

Enzyme replacement therapy is available for the Type I disease (Imiglucerase or Cerezyme)

Also miglustat (Zavesca) – an oral drug which inhibits the enzyme glucosylceramide synthase, an essential enzyme for the synthesis of most glycosphingolipids

Slide58

Miglustat (Zavesca)

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Genetic defects in ganglioside metabolism

Metachromatic leukodystrophyaccumulation of sulfogalactocerebroside (sulfatide) in the central nervous system of patient having a deficiency of a specific sulfatase

mental retardation, nerves stain yellowish-brown with cresyl violet dye (metachromasia)Generalized gangliosidosisaccumulation of ganglioside GM1deficiency of GM1 ganglioside:

b

-galactosidase

mental retardation, liver enlargement, skeletal involvement

Slide60

Niemann-Pick disease

principal storage substance: sphingomyelin which accumulates in reticuloendothelial cellsenzyme deficiency: sphingomyelinaseliver and spleen enlargement, mental retardation

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Blood groups

determined by various glycolipids on RBCsA antigens

B antigensH antigens

not recognized by anti-A or anti-B antibodies

(found on type O blood cells)

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Cholesterol and cholesterol esters

Slide63

STEROID NUMBERING SYSTEM

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STEREOCHEMISTRY OF STEROIDS

Slide65

Cholesterol sources, biosynthesis and degradation

diet: only found in animal fatbiosynthesis: primarily synthesized in the liver from acetyl-coA; biosynthesis is inhibited by LDL uptakedegradation: only occurs in the liver

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Cholesterol and cholesterol esters

The hydroxyl at C-3 is hydrophilic; the rest of the

molecule is hydrophobic; also 8 centers of asymmetry

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Cholesterol and cholesterol esters

Functions: -serves as a component of membranes of cells (increases or

moderates membrane fluidity

-precursor to steroid hormones

-storage and transport – cholesterol esters

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Functions of cholesterol

serves as a component of membranes of cells (increases or moderates membrane fluidity)precursor to steroid hormones and bile acidsstorage and transport –cholesterol esters

Slide69

Prostaglandins and other eicosanoids (prostanoids)

local hormones, unstable, key mediators of inflammationderivatives of prostanoic acid

Slide70

Slide71

Slide72

SUBSTITUTION PATTERN OF PROSTANOIDS

Slide73

Prostacyclins, thromboxanes and leukotrienes

PGH2 in platelets is converted to thromboxane A2

(TXA2) a vasoconstrictor which also promotes platelet aggregationPGH2 in vascular endothelial cells is converted to PGI2

, a vasodilator which inhibits platelet aggregation

Aspirin’s irreversible inhibition of platelet COX leads to its anticoagulant effect

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Functions of eicosanoids

Prostaglandins – particularly PGE1 – block gastric production and thus are gastric protection agents

Misoprostol (Cytotec) is a stable PGE1 analog that is used to prevent ulceration by long term NSAID treatmentPGE1

also has vasodilator effects

Alprostadil (PGE

1

) – used to treat infants with congenital heart defects

Also used in impotance (Muse)

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Functions of eicosanoids

PGF2a – causes constriction of the uterus

Carboprost; “Hebamate” (15-Me-PGF2a) – induces abortionsPGE2 is applied locally to help induce labor at term

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Examples of drugs derived from prostaglandins

Slide77

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Leukotrienes are derived from arachidonic acid via the enzyme

5-lipoxygenase which converts arachidonic acid to 5-HPETE

(5-hydroperoxyeicosatetranoic acid) and subsequently by

dehydration to LTA

4

peptidoleukotrienes

Leukotrienes

Slide79

Leukotrienes are synthesized in neutrophils, monocytes, macrophages,

mast cells and keratinocytes. Also in lung, spleen, brain and heart.

A mixture of LTC4, LTD4 and LTE4 was previously known as the

slow-reacting substance of anaphylaxis

peptidoleukotrienes

Leukotrienes

Slide80

Non-peptidoleuktrienes: LTA

4

is formed by dehydration of5-HPETE, and LTB

4

by hydrolysis of the epoxide of LTA

4

Leukotrienes

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Biological activities of leukotrienes

1. LTB

4 - potent chemoattractent - mediator of hyperalgesia - growth factor for keratinocytes

2. LTC

4

- constricts lung smooth muscle

- promotes capillary leakage

1000 X histamine

3. LTD

4

- constricts smooth muscle; lung

- airway hyperactivity

- vasoconstriction

4. LTE

4

- 1000 x less potent than LTD4

(except in asthmatics)

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Leukotriene receptor antagonists

Montelukast

(Singulair)

Zafirlukast

(Accolate)

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Lipid-linked proteins

Lipid-linked proteins (different from lipoproteins)lipoproteins that have lipids covalently attached to themthese proteins are peripheral membrane proteins

Slide84

Lipid-linked proteins

3 types are most common:Prenylated proteinsFarnesylated proteins (C15 isoprene unit)

Geranylgeranylated proteins (C20 isoprene unit)Fatty acylated proteinsMyristoylated proteins (C14)Palmitoylated proteins (C16)

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Lipid-linked proteins

glycosylphosphatidylinositol-linked proteins (GPI-linked proteins)occur in all eukaryotes, but are particularly abundant in parasitic protozoa

located only on the exterior surface of the plasma membrane

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Fatty acylated proteins

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Prenylated proteins

Slide88

GPI-linked proteins

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Lipoproteins

particles found in plasma that transport lipids including cholesterollipoprotein classes

chylomicrons: take lipids from small intestine through lymph cellsvery low density lipoproteins (VLDL)intermediate density lipoproteins (IDL)

low density lipoproteins (LDL)

high density lipoproteins (HDL)

Terpenes

Slide90

Lipoprotein class

Density (g/mL)

Diameter (nm)

Protein % of dry wt

Phospholipid %

Triacylglycerol % of dry wt

HDL

1.063-1.21

5 – 15

33

29

8

LDL

1.019 – 1.063

18 – 28

25

21

4

IDL

1.006-1.019

25 - 50

18

22

31

VLDL

0.95 – 1.006

30 - 80

10

18

50

chylomicrons

< 0.95

100 - 500

1 - 2

7

84

Composition and properties of human lipoproteins

most proteins have densities of about 1.3 – 1.4 g/mL and lipid aggregates usually

have densities of about 0.8 g/mL

Slide91

Lipoprotein structure

Slide92

LDL molecule

Slide93

The apolipoproteins

major components of lipoproteinsoften referred to as aproteins

classified by alphabetical designation (A thru E)the use of roman numeral suffix describes the order in which the apolipoprotein emerge froma chromatographic columnresponsible for recognition of particle by receptors

Slide94

HELICAL WHEEL PROJECTION OF A PORTION OF APOLIPOPROTEIN A-I

Slide95

LIPOPROTEINS

spherical particles with a hydrophobic core (TG and esterified cholesterol)apolipoproteins on the surface

large: apoB (b-48 and B-100) atherogenicsmaller: apoA-I, apoC-II, apoEclassified on the basis of density and electrophoretic mobility (VLDL; LDL; IDL;HDL; Lp(a)

Slide96

Apoproteins of human lipoproteins

A-1 (28,300)- principal protein in HDL90 –120 mg% in plasmaA-2 (8,700) – occurs as dimer mainly in HDL

30 – 50 mg %B-48 (240,000) – found only in chylomicron <5 mg %B-100 (500,000) – principal protein in LDL80 –100 mg %

Slide97

C-1 (7,000) – found in chylomicron, VLDL, HDL4 – 7 mg %

C-2 (8,800) - found in chylomicron, VLDL, HDL3 – 8 mg %C-3 (8,800) - found in chylomicron, VLDL, IDL, HDL8 15 mg %

D (32,500) - found in HDL8 – 10 mg %E (34,100) - found in chylomicron, VLDL, IDL HDL3 – 6 mg %

Apoproteins of human lipoproteins

Slide98

Major lipoprotein classes

chylomicronsdensity <<1.006

diameter 80 - 500 nmdietary triglyceridesapoB-48, apoA-I, apoA-II, apoA-IV, apoC-II/C-III, apoEremains at origin in electrophoretic field

Slide99

Major lipoprotein classes

VLDLdensity >1.006

diameter 30 - 80nmendogenous triglyceridesapoB-100, apoE, apoC-II/C-IIIprebeta in electrophoresis

Slide100

Major lipoprotein classes

IDL (intermediate density lipoproteins)density: 1.006 - 1.019

diameter: 25 - 35nmcholesteryl esters and triglyceridesapoB-100, apoE, apoC-II/C-IIIslow pre-beta

Slide101

Major lipoprotein classes

HDL (high density lipoproteins)density: 1.063-1.210

diameter: 5-12nmcholesteryl esters and phospholipidsapoA-I, apoA-II, apoC-II/C-IIIalpha (electrophoresis)

Slide102

Major lipoprotein classes

LDL (low density lipoproteins)density: 1.019 - 1.063

diameter: 18-25nmcholesteryl estersapoB-100beta (electrophoresis)< 130 LDL cholesterol is desirable, 130-159 is borderline high and >160 is high

Slide103

Cholesterol and lipid transport by lipoproteins

Slide104

Cholesterol and lipid transport by lipoproteins

Slide105

Slide106

Slide107

Photograph of an arterial plaque

Slide108

The LDL receptor

characterized by Michael Brown and Joseph Goldstein (Nobel prize winners in 1985)based on work on familial hypercholesterolemia

receptor also called B/E receptor because of its ability to recognize particles containing both apos B and Eactivity occurs mainly in the liverreceptor recognizes apo E more readily than apo B-100

Slide109

Representation of the LDL receptor

Slide110

Terpenes

simple lipids, but lack fatty acid componentformed by the combination of 2 or more molecules of 2-methyl-1,3-butadiene (isoprene)monoterpene (C-10) – made up of 2 isoprene units

sesquiterpene (C-15) – made up of 3 isoprene unitsditerpene (C-20) – made up of 4 isoprene units

Slide111

Monoterpenes

Monoterpenes are readily recognized by their characterisitic flavors

and odors ( limonene in lemons, citronellal in roses and geraniums,

pinene in turpentine and menthol from peppermint

Slide112

Sesquiterpenes

Slide113

Diterpenes

All-trans-retinal

Slide114

Triterpenes

Triterpenes are C-30 compounds are addition products of 2 sesquiterpenes;

Both squalene and lanosterol are precursors of cholesterol and other steroids

Slide115

Other terpenes

tetraterpenes (C-40) are not as common as mono, di, and triterpenesinclude the carotenoids such as beta-carotene (precursor of vitamin A) and lycopene found in tomatoes

usually colorful compounds due to highly conjugated systempolyisoprenoids or polyprenols consist of numerous isoprene adducts (8 – 22)

examples include dolichol phosphate, undecaprenyl alcohol (bactoprenol) and the side chains of vitamins K, vitamin E and coenzyme Q

Slide116

Websites on lipids

http://www.cyberlipid.org/ web site deals mainly with an overview on all lipids

http://www.lipidsonline.org – this website focuses mainly on disease processes (atherosclerosis) and treatmenthttp://www.lipidlibrary.co.uk/ -There are two main divisions in this website, one dealing with the chemistry and biochemistry of lipids and the other with the analysis of lipids

Slide117

The End