Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic...

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lipids • Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. • Chemically, lipids are defined as the esters of alcohol and fatty acids.

Transcript of Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic...

Page 1: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

lipids

• Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents.

• Chemically, lipids are defined as the esters of alcohol and fatty acids.

Page 2: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Lipids are composed of 3 fatty acids joined to an alcohol.

• Fatty acids and alcohol are the building block components of lipids.

• The lipids are the important constituents of diet due to their higher energy value.

• One gram of lipid yields 9.3 kilocalones of heat, while the same amount of carbohydrate or protein yields 4.5 kilocalories only.

Page 3: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• The lipids include a heterogenous group of compounds related to fatty acids.

• The common lipids are fats. oils, waxes, phosph olipids, glycolipids, cerebros ides, sulfolipids, aminolipids, steroids, terpenes, carotenoids, some hormones and some vitamins.

Page 4: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Lipids have three important properties.

1. Lipids are insoluble in water but soluble in non-polar organic solvents, such as acetone, alcohol, chloroform, benzene and ether.

• 2. They contain a large proportion of carbon and hydrogen bonds and release large amount of energy On breakdown.

• 3. On alkaline hydrolysis lipids yield alcohol and fattyacids.

Page 5: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Lipids are esters* of glycerol and fatty acids. They are formed by the combination of alcohol and fatty acids.

• Usually a lipid is made up of a glycerol and three fatty acids. Such a lipid is called a triglyceride or a neutral fat.

Page 6: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.
Page 7: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Ester is a compound formed by the combination of an acid with a glycerol with the removal of water.

Page 8: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Glycerol, a component of lipid.

It is an alcohol.

It is a trihydric alcohol.

It contains three alcoholic (OH) groups.

Of these three, two are primary alcoholic groups (CH2OH)

and the third one is secondary (CHOH).

Page 9: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Fatty acid: A long-chain carboxylic acid; those in animal fats and vegetable oils often have 12–22 carbon atoms.

• Lipid: A naturally occurring molecule from a plant or animal soluble in nonpolar organic solvents.

• Waxes are carboxylic acid esters, RCOOR’,with long, straight hydrocarbon chains in both R groups; they are secreted by sebaceous glands in the skin of animals and perform mostly external protective functions.

Page 10: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Triacylglycerols are carboxylic acid triesters of glycerol, a three-carbon trialcohol. They make up the fats stored in our bodies and most dietary fats and oils. They are a major source of biochemical energy.

Page 11: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Fatty Acids and Their Esters• The naturally occurring fats and oils are triesters

formed between glycerol and fatty acids.• Saturated fatty acid: A long-chain carboxylic acid

containing only carbon–carbon single bonds.• Unsaturated fatty acid: A long-chain carboxylic

acid containing one or more carbon–carbon double bonds.

• If double bonds are present in naturally occurring fats and oils, the double bonds are usually cis rather than trans.

Page 12: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Types of Fatty Acids

Page 13: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.
Page 14: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Trans Fatty Acids

The Truly Awful!

Page 15: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

The Good!

Page 16: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

The

Bad!

Page 17: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

TheTrulyAwful!

Page 18: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Fats are Used in Energy Storage and Production

Page 19: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

The figure is found at http://courses.cm.utexas.edu/archive/Spring2002/CH339K/Robertus/overheads-2/ch11_lipid-struct.jpg(Jan 2007)

Strcture of lipids

Page 20: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Glycerides

The major form of lipid in food and in the body

Page 21: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

The figure was adopted from http://en.wikipedia.org/wiki/Fatty_acid (April 2007)

Page 22: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Fatty Acids

• Fatty acids are aliphatic straight chain hydrocarbon compounds with a terminal carboxyl group. They are the building blocks of lipids.

Page 23: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.
Page 24: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.
Page 25: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• The carbon atoms are numbered from the carbon of the COOH group.

• In most of the unsaturated fatty acids there is a single double bond lying between carbon atoms 9 and 10.

• This is designated as . • The symbol with the superscript number• 9 indicates the position of the double bond.

Page 26: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• The symbol 18:0 denotes a C,8 fatty acid with no double bonds. The number 18:2 signifies that there are 2 double bonds.

• Similarly, the symbol 18:2; 9, 12 is used to denote an 18 carbon acid with two double bonds in the 9 and 12 positions.

• When two or more double bonds are present in a fatty acid, the double bonds are never conjugated But the double bonds are separated by a methylene group.

Page 27: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

a) Neutral fat (Triacylglycerol): • Esters of 3 fatty acids with glycerol • Glycerol is an alcohol containing 3 OH groups• Types:

– Simple: contain similar fatty acids e.g., tripalmitin– Mixed; contain different fatty acids e.g.,

palmito-oleio-stearin– Either solid, called fats, or liquid, called oils.

b) Waxes: – Esters of fatty acids with alcohols other than glycerol. – Important for manufacturing of ointments & cosmetics– Not digested

1- Simple lipids

Page 28: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Simple Lipids (Triglycerides)

• A simple lipid is formed when three molecules of fatty acids combine with one molecule of glycerol.

• In this process 3 molecules of water are released.

Page 29: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Monoglycerides

monopalmitin

• Diglycerides

dipalmitin

Page 30: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Polyunsaturated fatty acids have more than one C=C double bond.

Linoleic and linolenic acids are essential in the human diet because the body does not synthesize them and they are needed for the synthesis of other lipids.

Page 31: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.
Page 32: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Compound lipids

• contain some chemical groups in addition to fatty acids and glycerol.

• When a lipid contains a phosphate group, it is called a phospholipid and when a lipid contains a carbohydrate, it is called a glycolipid.

Page 33: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Lecithin is a phospholipid. In lecithin, two hydroxyl groups of glycerol have been esterified by fatty acids, while the third hydroxyl group has been replaced by phosphoric acid which in turn has formed an ester with choline.

Page 34: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

PhospholipidLecithin, a common food additive, is a phospholipid.

Embedded in cell membranes.

Page 35: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Derived lipids• Steroids:

• The steroids have a 1,2_cycIopentanoperhydro phenanthrene nucleus. It has four rings named as A, B, C and D. The rings A, B and C are hexagons called cyclohexane rings.

• The ring D is a pentagon called cyclopentane.

Page 36: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Steroids• Steroids are solid alcohols.

• They have a

cyclo pentano per hydro phenanthrene nucleus.

• They are made up of four rings named as A,B,C and D.

• The rings A, B and C are cyclohexanes. The ring D is a cyclopentane. The numbering starts from ring A to D.

Page 37: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

it has two methyl groups (CH3 ) at carbon atoms 10 and 13. Usually there is a side chain at position 17. Cholesterol is a steroid.

Page 38: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Terpenes

• derivatives of isoprene (= 2-methylbuta-1,3-diene)

• found in oils of plants and flowers• characteristic odour (geraniol, menthol,...)• steroids are derived from triterpenes

Page 39: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Terpenes• Terpenes are hydrocarbons. They have less

than 40 carbon atoms.

• Terpenes are constructed out of isoprene units.

• Each isoprene unit has 5 carbon atoms and 8 hydrogen atoms (C5H8). Each isoprene unit has two ends, namely a head and a tail. The head is the branched end and the tail is the unbranched

Page 40: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Terpenes – classification:

• monoterpenes (C10) 2 x isoprene

• sesquiterpenes (C15)3 x isoprene

• diterpenes (C20) 4 x isoprene

• triterpenes (C30) 6 x isoprene

• tetraterpenes (C40) 8 x isoprene

formed by bonding „head to tail“ or „tail to tail“

different degree of unsaturationvariety of functional groups

Page 41: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• When the terpene contains two isoprene units, it is called a monoterpene, When it contains 3 units, it is called a sesquiterpene.

• When it contains 4 units the terpene is called

• a diterpene.

• A triterpene contains 6 units.

• When there are 8 units the terpene is called a tetraterpene.

• A polyterpene contains more than 8 isoprene units.

Page 42: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

menthol (C10) phytol (C 20)

squalene (C 30)

-carotene (C40)

The figures are adopted from http://en.wikipedia.org (April 2007)

Examples of terpenes

Page 43: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• The commercial name for glycerol is glycerine,

• It soluble in water and insoluble in organic solvents.

• Glycerol combines with three similar fatty acids to form a simple lipid called triglyceride with the release of 3 molecules of water.

Glycerol has two important properties. They are

1. Formation of esters

2. Dehydration

Page 44: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• 1. Formation of Esters• Glycerol reacts with acids, both organic and inorganic

acids, to form esters like monoesters, diesters and triesters,

• Triesters of glycerol with higher fatty acids constitute lipids• Monoglycerides act as good detergents and

emulsifying agents. This property helps in the manufacture of detergents. In animals, emulsifying property helps the digestion of fats.

• 2. Dehydration• When glycerol is heated in the presence of a dehydrating

agent like H2S04, phosphorus pentoxide or potassium hydrogen sulphate (KHSO4), it produces an unsaturated aldehyde called acrylic aldehyde or acrolein.

Page 45: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.
Page 46: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.
Page 47: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• The common higher fatty acids are insoluble in• water.• But they can be dispersed into micelles in dilute

NaOH Or KOH.• Micelle is an aggregation of fatty acid molecules• In water into a globular structure in which their

non-polar• tails are in the interior and the polar heads are on

the exterior exposed to water.• NaOH or KOH converts fatty acids into soaps.

Soaps are the salts of fatty acids.

Page 48: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Again, based on their requirement in the diet, fatty• acids are classified into two types namely• 1. Essential fatty acids• 2. non- essential fatty acids• Thus fatty acids are classified into 6 types. They

are• 1.unsaturated fatty acids• 2. saturated fatty acids• 3. hydroxy or oxygenated fatty acids• 4. Cyclic fatty acids• 5. essential fatty acids• 6. Nonessential fatty acids

Page 49: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.
Page 50: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.
Page 51: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

The hydrocarbon chains in saturated acids are flexible and uniform in shape, allowing them to nestle together. By contrast, the carbon chains in unsaturated acids have rigid kinks wherever they contain cis double bonds. The kinks make it difficult for such chains to fit next to each other in the orderly fashion necessary to form a solid.

Page 52: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

The more double bonds there are in a triacylglycerol, the harder it is for it to solidify.

Page 53: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.
Page 54: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Waxes

• Waxes have the general structure shown here. R` and R represent long carbon chains of approximately 30 carbons resulting in an extremely hydrophobic lipid with a high degree of water repellency.

• An important biological function of a wax is to act as a protective coating.

The “shine” on these leaves is due to a thick protective wax coating.

Notice that a wax is an ester.

Page 55: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Cholesterol (and other lipids) in the body must be packaged for transport because lipids will aggregate in the aqueous environment of the bloodstream. The liver packages dietary lipid into aggregates known as very-low-density-lipoproteins (VLDL).

• The improper transport of cholesterol in the bloodstream can lead to atherosclerosis, a metabolic disease

Cholesterol and Atherosclerosis

A cutaway of VLDL.

The VLDL has only a single layer

The interior of theVLDL is hydrophobic

Page 56: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

The proper transport of lipids through the bloodstream and distribution to tissues depend on the following lipoproteins: VLDL (very low density lipoprotein), LDL (low density lipoprotein) and HDL (high density lipoprotein). These

lipoproteins are shown in the diagram below.

Page 57: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

properties

• physical State• Fats containing saturated fatty acids are

solids. Animal fats are solids. • Fats containing unsaturated fatty acids

are liquids. Plant fats are oils at room temperature.

• Oily and Greasy• Lipids are greasy to touch and they leave

an oil impression on paper.

Page 58: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Properties of Fats and Oils

• Triacylglycerols in natural fats and oils are nonpolar, hydrophobic molecules with no ionic charges.

• Oil: A mixture of triacylglycerols that is liquid because it contains a high proportion of unsaturated fatty acids.

• Fat: A mixture of triacylglycerols that is solid because it contains a high proportion of saturated fatty acids.

Page 59: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Solubility;• Fats are sparingly soluble in water, i.e. fats are hydrophobic.

• They are highly soluble in organic solvents like alcohol, ether, etc.

• Solubility decreases with increasing molecular weight.

• Fats containing hydroxyl groups are more soluble than fats without hydroxyl groups.

Melting point• Melting point of fatty acids increases with increase in

molecular weight. • Saturated fatty acids are having higher melting points than

fatty acids with unsaturated bonds.

Page 60: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

SpecifiC Gravity• Specific gravity is less than water. So they are

floating on the water surface. Solid fats are lighter than liquid fats (oil).

isomerism• Due to the presence of double bonds in

unsaturated fatty acids, geometrical isomerism (cis-trans) is possible.

insulation• Fats are bad conductors of heat. Fats in the

subcutaneous tissues provide a sort of blanket for warm blooded animals. For cold blooded animals there is a little amount of fat in the subcutaneous regions. A high temperature is maintained by fat.

Page 61: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Emulsification• In water fats are broken into minute droplets

an dispersed. This is called emulsification.

• Emulsion is a mixture of lipids and water. Milk is a naturally occurring emulsion.

• Emulsification greatly increases the surfaces area of fats It is an essential requisite for digestion of fats. Emulsification is brought about by mechanical action and by the action of bile salts.

Page 62: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Hydrolysis of fats and oils carried out by strong aqueous bases to form soaps is called saponification.

Page 63: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Micelle: A spherical cluster formed by the aggregation of soap or detergent molecules so that their hydrophobic ends are in the center and their hydrophilic ends are on the surface.

Page 64: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Rancidity• Rancidity is the ill-smelling of fat. It is caused

by rancidification. Rancidification is due to autooxidation of fats.

• The fat which has become rancid has a disagreeable odour and taste and is unfit for consumption.

• Rancidification occurs more frequently in summer. The chemical changes which occur during rancidification are called rancidity

• Rancidity occurs in two ways. • They are hydroxyl rancidity and oxidative rancidity.

Page 65: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Bloor’s Criteria• According to Bloor, lipids are compounds having

the following characteristics.• (i) They are insoluble in water.• (ii) Solubility in one or more organic solvents,

such as ether, chloroform, Benzene, Acetone, etc—so called ‘fat solvents’.

• (iii) Some relationship to the fatty acids as esters• —either actual or potential.• (iv) Possibility of utilisation by living organisms.• Thus, lipids include fats, oils, waxes and related

compounds.

Page 66: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• BREAKDOWN PRODUCT OF FATS ARE ACETYL CO A USED FOR SYTHESIS OF CHOLESTEROL AND HORMONES

• Some vitamins like, A, D, E and K are fat soluble, hence lipid is necessary for these vitamins.

Page 67: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• II. Compound Lipids• Esters of fatty acids containing groups, other than, and in

addition, to an alcohol and fatty acids.• (a) Phospholipids: They are substituted fats containing in

addition to fatty acid and glycerol, a phosphoric acid residue, a nitrogenous base and other substituents.

• Examples—phosphatidyl choline (Lecithin), phosphatidyl ethanolamine (Cephalin),

phosphatidyl insositols (Lipositols), phosphatidyl serine, plasmalogens, sphingomyelins etc.• (b) Glycolipids: lipids containing carbohydrate moiety are

called glycolipids. They contain a special alcohol called sphingosine or sphingol and nitrogenous base in addition to fatty acids But does not contain phosphoric acid o’-glyceroL These are of two types:

• (i) Cerebrosides• (ii) Gangliosides

Page 68: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• (c) Sulfolipids: Lipids characterized by possessing sulphate groups.

• (d) Aminolipids (Proteoipids)

• (e) Liproproteins: Lipids as prosthetic group to proteins.

Page 69: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

DERIVED LIPIDS

• (a) Saturated FA• There general formula is CnH2n+1 COOH

Examples:

• Acetic acid CH3COOH• Propionic acid C2H5COOH• Butyric acid• Caproic acid• Palmitic acid• Stearic acid

Page 70: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

1. Saturated fatty acids:– Fatty acids containing no double bonds– Examples of saturated FA:

• Butyric acid (4C): CH3–CH2–CH2–COOH• Palmitic acid (16C ): CH3–(CH2)14–COOH• Stearic acid (18C): CH3–(CH2)16–COOH

2. Unsaturated fatty acids:• Fatty acids containing double bond(s). • They are either monounsaturated (one double bond) or polyunsaturated

(more than one double bond).• Double bonds are:

– Nearly always in the cis configuration– Spaced at 3 carbon interval if the fatty acid has more than one double

bond, • Example of monounsaturated fatty acids:

– Palmitoleic (16C) is written 16:1Δ9 , – Oleic (18C) is written 18:1Δ9

• Examples of polyunsaturated fatty acids : – Linoleic acid (18C) is written 18: 2 ∆9,12

– Linolenic (18C) is written 18:3 ∆9,12,15

– Arachidonic (20C) is written 20: 4 ∆5,8,11,14

Page 71: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Essential Fatty acids:• They are the polyunsaturated fatty acids:

» linoleic acid 18: 2 ∆9,12» linolenic acid 18:3 ∆9,12,15

• Must be supplied in the diet because the body can not form them (we lack enzymes required to introduce double bonds after C9)

• They are present mainly in vegetable oils• Arachidonic acid (20C) is formed in the body from

linoleic acid, it becomes essential only if linoleic acid is deficient

Non essential Fatty acids:• They can be formed in the body • They are the saturated & the monounsaturated fatty

acids

Page 72: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Unsaturated FA

• (1) Mono unsaturated (Mono-Ethenoid) fatty acids are those which contain one double bond.

• Example: Oleic acid is found in nearly all fats. (formula: 18: 1; 9).

• (2) Polyunsaturated (Polyethenoid) fatty acids:

• There are three polyunsaturated fatty acids of biological importance.

Page 73: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• (1) Linoleic acid series (18:2; 9, 12): It contains two double bonds between C9 and C10; and between C12 and C13.

• Their general formula is CnH2n-3 COOH Dietary sources—Linoleic acid is present in sufficient amounts in peanut oil, corn oil, cotton seed oil, soybean oil and egg yolk.

• (ii) Linolenic acid series (18 : 3 ; 9, 12, 15): It contains three double bonds between 9 and 10 ; 12 and 13; and I5 and 16. Their general formula is CnH2n-5 COOH.

• Dietary Source: Found frequently with linoleic acid, but particularly present in linseed oil, rape seed oil, soybean oil, fish visceras and liver oil (cod liver oil).

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• (iii) Arachidonic acid series (20 : 4; 5, 8, 11, 14): It contains four double bonds

• Their general formula: Cn,H2n-7COOH

• Dietary source: Found in small quantities with linoIeic acid and linolenic acid but particularly found in peanut oil. Also found in animal fats including Liver fats.

Page 75: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Nomenclature

• (i) Saturated acids end in “anoic” e.g., octanoic acid and

• (ii) unsaturated acids with double bonds end in “enoic” e.g., octadecenoic acid (oleic acid).

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• lack of EFA in the diet can product growth retardation and other deficiency manifestation symptoms.

• Experimental studies:

• Burt and Burr (1929) first observed that rats maintained on a diet from which fats are rigidly exciuded—they cease to grow, develop scaliness of the skin, necrosis of the tail, kidney damage and impaired reproductive capabilities. These abnormalities were prevented/cured when 100 mg/day of Linoleic acid or Arachidonic acid were included in the diet.

Page 77: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Linoleic acid is most important as, arachidonic acid can be formed from Linoleic acid by a three stage reaction by addition of Acetyl — CoA as follows.

• Pyridoxal phosphate is necessary for this conversion.

• (i) Activation step: Linoleic acid is activated.

• CoA ester of linoleate undergoes dehydrogenation to form — Linolenate.

• .

Page 78: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• (ii) Addition of two carbon moiety: Linolenate Is converted to Eicosatrienoate by addition of 2 carbon unit—acetyl —CoA either in mitochondrion or through malonyl — CoA in microsome.

• Pyridoxal phosphate is required as cofactor.• (iii) Dehydrogenation step: By another

dehydrogenation Eicosatrienoate is converted to Arachidonic acid

Page 79: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• 3. Synthesis of prostaglandins and other compounds: Prostaglandins are synthesized from Arachidonic acid by cyclooxygenase enzyme system.

• Leukotrienes are a newly discovered family of conjugated trienes formed from Arachidonic acid in leucocytes by the Lipoxygenase pathway. /

Page 80: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Effect on clotting time: Prolongation of clotting time is noted in ingestion of fats rich in EFA.

• Role in vision: Docosahexenoic acid is the most abundant polyeneoic fatty acids present in retinal photoreceptor membranes.

• Docosahexenoic acid is formed from dietary linolenic acid.

• It enhances the electrical response of the photo- receptors to illumination. Hence linolenic acid is necessary in the diet for optimal vision.

Page 81: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Unsaturated Alcohols• Among the unsaturated alcohols found in fats,

many of them are pigments. These include:• (a) Phytol (Phytyl alcohol): A constituent of

chlorophyll.• (b) Lycophyll: A polyunsaturated dihydroxy

alcohol which occurs in tomatoes as a purple pigment.

• (c) Carotene: Easily split in the body at the central point of the chain to give two molecules of alcohol, vitamin A.

• (d) Sphingosine or sphingol: An unsaturated amino alcohol present in body as a constituent of phospholipid, sphingomyelin and various glycolipids.

Page 82: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Solid bile

Page 83: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Normal level of serum total cholesterol in an adult varies from 150 to 250 mg%. About 40-50 mg% occurs as “free” cholesterol (approx 30% of total)

Page 84: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Colour Reactions of Sterols

• (a) Liebermann-Burchard Reaction

• A chlorofom solution of a sterol, when treated with acetic anbydride and conc.H2SO4 gives a grass-green colour..

• This reaction forms the basis for a colorimetric estimation of cholesterol by Sackett’s method.

Page 85: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• (b) Salkowski Test

• When a chloroform solution of the sterol is treated with an equal volume of Conc H,S04 develops a red to purple colour.

• The heavier acid, which forms a layer below assumes a yellowish colour with a green fluorescence, whereas the upper chloroform layer becomes bluish red first, and gradually turns violet-red.

Page 86: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• (c) Formaldehyde-Sulphuric Acid Test

• On adding a 1:50 mixture of formaldehyde and sulphuric acid to a

chloroform solution of cholesterol, the chloroform layer turns cherry-red. Addition of acetic anhydride to the chloroform layer (after separating it from the previous mixture)

• changes the cherry-red colour to blue.

Page 87: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Zak’s Reaction

• When glacial acetic acid,

• aldehyde free, solution of cholesterol

• is treated with

• ferric chloride and conc. H,S04,

• produces a red colour.

• This reaction forms a basis for the colorimetric estimation ot cholesterol (Zak’s method).

Page 88: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

Saponification Number• Definition: The number of mgms of KOH

required to saponify the free and combined FA in one gram of a given fat is called its saponification number.

• Fats containing short chain fatty acids will have more –COOH group present .and hence will take up more alkali – high saponification number

Page 89: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Acid Number

• Definition: Number of mgms of KOH required to neutralise the fatty acids in a gm. of fat is known as the acid number.

• Significance: The acid number indicates the degree of rancidity of the given fat.

• Polenske Number

• Definition: The number of milli litre of 0.1 normal KOH required to neutralize the insoluble fatty acids from 5 gram of fat.

Page 90: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Relchert-Meissl Number

• Definition: it is the number of millilitres of 0.1 (N) alkali required to neutralise the soluble volatile fatty acids distilled from 5gm. of fat.

Page 91: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Significance: • The Reichert-Meissl measures the amount of volatile soluble fatty acids

• Butter fat is the only common fat with a high Reichert-Meissi number and this determination, therefore, is of interest in that it aids the food chemist in detecting butter substitutes in food products.

Page 92: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Iodine Number• The unsaturated fatty acids take up iodine and

other halogens at the point of unsaturation, yielding saturated halogen derivatives. Consequently,

• the degree of unsaturation of fats may be determined by ascertaining how much Iodine a given quantity will absorb.

• The result is called the Iodine number.

• Definition: Iodine number is defined as the number of grams of iodine absorbed by 100 gms. of fat.

Page 93: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Acetyl Number• Some of the fatty acid residues in fats contain• —OH groups.• In order to determine the proportion of these, they

are acetylated by means of acetic anhydride. Thus an acetyl group is introduced where ever a free — OH group is present.

• After washing out the excess acetic anhydride and acetic acid liberated,

• the acetylated fat can be dried and weighed and the acetic acid in combination determined by titration with standard alkali after it has been set free.

• The acetyl number is thus a measure of the number of — OH group present

Page 94: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.
Page 95: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Glycerophosphatides: in this glycerol is the alcohol group. Examples are

phosphatidyl ethanolamine(cephalin), phosphatidyl choline (Lecithin), phospatidyl serine, plasmalogens, phosphatidic acid and cardio-lipins, phosphatides.

• Phospho-inositides: In this group, inositol is the alcohol e.g., phosphatidyl inositol (lipositol)

• Phospho-sphmgosides: Alcohol present is sphingosine (also called as sphingol) — an unsaturated amino alcohol. e.g., sphingomyelin.

Page 96: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.
Page 97: Lipids Lipids are water insoluble, oily or greasy organic compounds soluble in non-polar organic solvents. Chemically, lipids are defined as the esters.

• Melting Points of Saturated vs. Unsaturated Fatty Acids:• Note that as a group, the unsaturated fatty acids have lower

melting points than the saturated fatty acids.• The reason for this phenomenon can be found by a careful

consideration of molecular geometries. The tetrahedral bond angles on carbon results in a molecular geometry for saturated fatty acids that is relatively linear although with zigzags. See graphic on the left.

• This molecular structure allows many fatty acid molecules to be rather closely "stacked" together. As a result, close intermolecular interactions result in relatively high melting points.

• On the other hand, the introduction of one or more double bonds in the hydrocarbon chain in unsaturated fatty acids results in one or more "bends" in the molecule. The geometry of the double bond is almost always a cis configuration in natural fatty acids. These molecules do not "stack" very well. The intermolecular interactions are much weaker than saturated molecules. As a result, the melting points are much lower for unsaturated fatty acids.