Lipids - PowerPoint Presentation

Slide1

LipidsSlide2

Lipids are non-polar

(hydrophobic)

organic compounds, insoluble in water,

soluble in organic

solvents (ether, acetone, carbontetrachloride). They contain carbon, hydrogen, and oxygen; sometimes nitrogen and phosphorus. In most cases they yield fatty acids on hydrolysis.They take place in lipid and plant metabolism.

What are Lipids? Slide3

Fatty acids

Fatty acids (FAs)

consist of hydrocarbon chain with a carboxylic acid at one end

 straight-chain organic acids

Most naturally occurring fatty acids have an even number of carbon atoms

They can be saturated and unsaturated.

Unsaturated fatty acids

have

lower melting points than saturated fatty acid.Slide4

Fatty acids

Monounsaturated FAs

 one double bond

Polyunsaturated FAs many double bonds

Eicosanoids (include prostaglandins,

leukotriens

,

prostacyclins

,

thromboxanes)

Double

bonds

in fatty acids are usually in the

cis

configuration.Slide5
Slide6

Linoleic acid is a nutritionally e

ssential

fatty

acid

. that must be ingested by

humans and other animals because the body requires

it

but cannot synthesize

it.It is found in large conc. in corn, peanut, soyabean oils but not in olive oil.

Absence of linoleic acid by infants

 weight loss and ezema.

Linoleic acidSlide7

Classification of lipids according to their structuresSlide8

Classification of lipids according to their structures

Simple lipids

 esters of FAs (

FAT, OIL, WAX

) [One or two chemical identities) Hydrolysis of a simple lipid  Simple lipid + H2Ofatty acid + alcoholIf the alcohol is glycerol (

FAT

or

OIL

)

If the alcohol is a monohydric alcohol



WAX

Hydrolysis of

complex lipids

more fatty acids + alcohol +other compoundPhospholipid

+ H

2

O (hydrolysis) FA + alcohol + phosphorus + nitrogen compound.

Phospholipids 

phosphoglyceride

or

phosphosphingoside

Glycolipid

+ H

2

O (hydrolysis)  FA +a carbohydrate +

sphingosineSlide9

Precursor lipids 

compounds resulting from hydrolysis of simple or complex lipids (FA,

sphingosine

)

Derived lipids lipids which are formed due to the transformation of fatty acids (Prostaglandins, Fat-soluble vitamins)Classification of lipids according to their structuresSlide10

Fats and oils

Fats with a melting point below room temperature are called oils.Slide11

Iodine number

The iodine number of a fat or an oil is the umber of grams of iodine that will react with the double bond present in 100 g of fat or oil

Higher iodine number higher degree of

unsaturation

Generally iodine number of animal fats < iodine number of vegetable oilsIodine number of fats <70Iodine number of oils > 70 Slide12

Some uses of lipids in the body

Fats serve as fuel.

Fats serve as reserve supply of food and energy.

Fats are stored in special adipose tissues and serve as a protector for vital organs.

Fats act as heat insulators.Some lipids allow rapid propagation of electrical signals.Slide13

Physical properties

White or yellowish solid or liquids

Pure fats and oils are odorless and tasteless. Over a period of time they become rancid and develop an unpleasant odor and

tatse

.Lighter than water.When shaken with water  temporarily emulsion.Emulsion can made permanent by addition of emulsifying agent such soap.Fats and oils must be emulsified before they can be digested. Slide14

Chemical reactions

Hydrolysis

3. EnzymeSlide15

SaponificationSlide16

Hydrogenation

In Practice not all double bonds are hydrogenated.

Hydrogenation lowers the iodine number. Slide17

Acrolein

test: Test for fats or oils which contain glycerol

Glycerol (KHSO

4

) (heat)Acrolein (strong odor)Rancidity: unpleasant odor or taste developed when fats stand at room temperature for a short period of time.Rancidity is due to hydrolysis and oxidation reactions.Oxidation of double bonds  short chain

aldehydes

and acids bad odor and taste (Antioxidant

Vit

. E and C.)

Fats + Water in butter (in presence of microorganisms)hydrolysis of fats Butyric acid disagreeable odor.

Fats and foods containing fats have to be covered and stored in the refrigerator Slide18

Cleansing action of soaps

CH

3

-(CH

2)16-COONa (Sodium stearate) Non-Polar Polar Hydrophopic Hydrophilic

Micelle

Mechanical Washing causes the oil to break down into small drops

Soap emulsifies then the oil and prevents it from coalescing.

Soap acts also as surfactant

 lowers surface tension

Slide19

Detergents

Synthetic compounds used as cleansing agents.

Soaps do not work in hard water  insoluble Ca and Mg salts

Detergents work also in hard water

Soaps (alkaline); Detergents (neutral)  Detergents can be used on silks and wool; Sops not. Detergents: Sodium salts if long chain alcohol sulfatesExample: Sodium laurylsulfateC12H

23

OH + H

2

SO

4 C11H

23

CH

2

OSO

3H + H2O

C

11

H

23

CH

2

OSO

3

H +

NaOH

 C

11

H

23

CH

2

OSO

3

Na + H

2

O Slide20

Complex lipids and cell Membranes: an overview

Some functions of membranes (40-50% lipids; 50-60% Proteins)

Mechanical support.

Seperate contents of the cells from the environment

Structural support for proteins (pumps; receptors)Slide21

Biochemistry II

Self aggregation of lipids

Introduction to lipids

Polar end

(hydrophilic end)

non-polar end

hydrophobic end)Slide22

Glycerophospholipids

Glycerophospholipids

(

phosphoglycerides), are common constituents of cellular membranes.They have a glycerol backbone.Hydroxyls at C1 & C2 are esterified to fatty acids.

An

ester

forms when a hydroxyl reacts with a carboxylic acid, with loss of H

2

O.Slide23

Phosphatidate

In

phosphatidate

:

fatty acids are esterified to hydroxyls on C1 & C2the C3 hydroxyl is esterified to Pi.Slide24

In most

glycerophospholipids

(

phosphoglycerides), P

i is in turn esterified to OH of a polar head group (X): e.g., serine, choline, ethanolamine, glycerol, or inositol. The 2 fatty acids tend to be non-identical. They may differ in length and/or the presence/absence of double bonds.Slide25

Phosphatidylinositol

, with inositol as polar head group, is one glycerophospholipid.

In addition to being a membrane lipid, phosphatidylinositol has roles in cell signaling.Slide26

Phosphatidylcholine

, with choline as polar head group, is another glycerophospholipid.

It is a common membrane lipid. Slide27

Each glycerophospholipid

includes

a

polar

region: glycerol

,

carbonyl

O

of fatty acids, Pi, & the polar head group (X

)

non-polar

hydrocarbon tails of fatty acids (

R

1, R2). Slide28

Structure of phospholipidsSlide29

Sphingosine may be reversibly phosphorylated to produce the

signal

molecule

sphingosine-1-phosphate

. Other derivatives of sphingosine are commonly found as constituents of biological membranes.Sphingolipids are derivatives of the lipid sphingosine, which has a long hydrocarbon tail, and a polar domain that includes an amino group. Slide30

In the more complex

sphingolipids

, a

polar “head group" is connected to the terminal hydroxyl of the sphingosine

moiety of the ceramide. The amino group of sphingosine can form an amide bond with a fatty acid carboxyl, to yield a ceramide. Slide31

Sphingomyelin, with a phosphocholine head group, is similar in size and shape to the glycerophospholipid phosphatidyl choline.

Sphingomyelin

has a

phosphocholine

or phosphethanolamine head group. Sphingomyelins are common constituent of plasma membranes.Slide32

Cholesterol is largely

hydrophobic

.

But it has one polar group, a

hydroxyl, making it amphipathic. Cholesterol, an important constituent of cell membranes, has a rigid ring system and a short branched hydrocarbon tail. Slide33

Structural features of cholesterol (

Chol

) and

cholesteryl esters (Chol-esters)

Cholesterol

Four fused hydrocarbon rings (A, B, C, and D, called the "

steroid nucleus

"

C8 branched hydrocarbon chain attached to C17

Hydroxyl group at C-3

Double bond between C-5 and C-6

Sterols

: Steroids with 8 to 10 C in

sides chain

and

hydroxyl group at C-3

Cholesterol does not occur in plants

Cholesteryl

esters

Most plasma cholesterol is in an

esterified

form.

More hydrophobic than

Chol

Not in membranes Slide34

Cholesterol

inserts into bilayer membranes with its hydroxyl group oriented toward the aqueous phase & its hydrophobic ring system adjacent to fatty acid chains of phospholipids.

The

OH

group of cholesterol forms hydrogen bonds with polar phospholipid head groups.Slide35

Two strategies

by which phase changes of membrane lipids are avoided:

Cholesterol

is abundant in membranes, such as plasma membranes, that include many lipids with long-chain saturated fatty acids.

In the absence of cholesterol, such membranes would crystallize at physiological temperatures.The inner mitochondrial membrane lacks cholesterol, but includes many phospholipids whose fatty acids have one or more double bonds, which lower the melting point to below physiological temperature. Slide36

Biochemistry II

Membrane lipids / Cholesterol

Introduction to lipids

Testosterone, the male sex hormone, is produced in the testes.

Estradiol, one of the female sex hormones, is produced in the ovaries and placenta.

Cortisol and aldosterone are hormones synthesized in the cortex of the adrenal gland; they regulate glucose metabolism and salt excretion.

Prednisolone and prednisone are synthetic steroids used as antiinflammatory agents. Slide37

Anabolic steroids (Athletes)

Testosterone

Increase of body mass, strength

Side effects (men)  liver cancer, impotence

HypercholesterolemiaBreast growthSide effects (women) increased amount of body hairVoice deepeningMenstrual irregularities Slide38

Biochemistry II

Membrane lipids / Cholesterol

Introduction to lipids Slide39

Atherosclerosis

Form of ateriosclerosis resulting from the deposition of lipids, primarily TAGs, and Chol, from the blood stream

Chol. is the larger threat

We have to reduce lipid intake

Unstaurated fish and vegetable oil  Loweing of Chol levelNormal Chol level = 200-220 mg/dlElevated Chol level should be cotrolled by dietIn extreme cases  cholesterol lowering drungs (pravastatin, lovastatin) Slide40

GM2

Sphingomyelin

G

lycosphingolipids differ from sphingomyelin in that they do not contain phosphate

.

T

he polar head function is provided by a monosaccharide or oligosaccharide attached directly to the

ceramide by an o-glycosidic bond.

Structure Of glycosphingolipidsSlide41

The simplest neutral

(uncharged)

glycosphingolipids are the cerebrosides

(ceramide + galactose or ceramide + glucose).

They serves primarily as an intermediate in the synthesis and degradation of the more complex glycosphingolipids).The cerebroside are found predominantly in the brain and peripheral nervous tissue.Ceramide oligosaccharides (or globosides) are produced by attaching additional monosaccharides (including GalNAc).Neutral glycosphingolipidsO

O

H

O

O

H

O

O

O

H

O

O

H

H

O

H

O

(

C

H

2

)

1

2

C

H

N

(

C

H

2

)

1

6

C

H

3

O

O

H

La

c

tosylceramid

e

(Gal-

b

1,4-Glc-

b

1,1'-Cer)

globo-

GalNAc-

b

1,3-Gal-

a

1,4-

O

H

O

O

H

N

H

A

c

H

O

H

O

O

O

H

O

O

O

H

Gala

c

tosylceramid

e

H

O

O

H

O

O

H

O

(

C

H

2

)

1

2

C

H

3

H

N

(

C

H

2

)

1

6

C

H

3

O

H

O

H

Glucosylceramide

H

O

O

H

O

O

H

O

(

C

H

2

)

1

2

C

H

3

H

N

(

C

H

2

)

1

6

C

H

3

O

H

H

O

O

OSlide42

Eicosanoids participate in many processes in the body

:

I

nflammatory

response that occurs after infection or injury with symptoms such as pain, swelling, and

fever

. An exaggerated or inappropriate

expression of the normal inflammatory response may occur in individuals

who have allergic or

hypersensitivity

reactions

C

ontraction

of smooth muscles (particularly in the intestine and uterus)

I

ncrease

in the

excretion

of

water

and

sodium

by the kidney

Regulation of

blood pressure

Regulation

of

bronchoconstriction

and

bronchodilation

(modulators)

Functions

of

the

EicosanoidsSlide43

Biosynthesis

of

the

EicosanoidsSlide44

Cyclooxygenase Pathway: Synthesis of the

Prostaglandins and Thromboxanes

1.

Synthesis of PGH2Oxidative cyclization of free arachidonic acid by prostaglandin endo-peroxide synthase  PGH2 !!!!PGH

2!!!!



variety of prostaglandins and thromboxanes

Prostaglandin endoperoxide synthase-2 activities (COX and peroxidase)

2 isoenzymes (COX1 and COX2)

[2 O

2

molecules]

COX1: (in most tissues): maintenance of healthy gastric tissue, renal homeostasis, and platelet aggregation.

COX2: (

inducible in a limited number of tissues) in response to products of activated immune and inflammatory cells. Slide45

Cyclooxygenase Pathway: Synthesis of the

Prostaglandins and Thromboxanes

2. Inhibition of prostaglandin synthesis

Cortisol (a steroidal anti-inflammatory agentinhibition of PLA2, COX2 but not COX1.NSAIDS (nonsteroidal anti-inflammatory agents (e.g. Aspirin) inhibition of COX1 and COX2 damage to the stomach and the kidneys, and impaired clotting of blood, is the basis of aspirin's toxicity.

Specific inhibitors for COX2 (for example,

celecoxib1

) are designed to reduce pathologic inflammatory processes while maintaining the physiologic functions of COX2.