Lipids

They are esters of long-chain fatty acids and alcohols, or of closely related derivatives.

They are related by their:

- Solubility in non polar organic solvents (e.g. ether, chloroform, acetone & benzene) - Insolubility in water.

Although the term lipid is sometimes used as a synonym for fats, fats are a subgroup of lipids called triglycerides.

Although humans and other mammals use various biosynthetic pathways to both break down and synthesize lipids, some essential lipids cannot be made this way and must be obtained from the diet .

Types of lipids :

• Oils• Fats• Waxes

The chief difference between these substances oils, fats, and waxes:

is the type of alcohol

• Glycerol combines with the fatty acids, (oils and fats).• A higher molecular weight, e.g. acetyl alcohol combines with

the fatty acids, (waxes).  Glycerol: a type of alcohol with a hydroxyl group on each of its three

carbons) and three fatty acids joined by dehydration synthesis. Since there are three fatty acids attached, these are known as triglycerides .

• Triglyceride- A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids- Chemical formula: C55H98O6.- There are many triglycerides: depending on the oil source, some are highly unsaturated, some less so.

Fatty acid• Fatty acid is a carboxylic acid with a long chain (aliphatic)

tail.• The long hydrocarbon chain, making it hydrophobic (tail).• The carboxyl group is hydrophilic (head).• Most naturally occurring fatty acids have a chain of an

even number of carbon atoms, from 4 to 28.• Fatty acids are usually derived (synthesized) from

triglycerides or phospholipids.

• When they are not attached to other molecules, they are known as "free" fatty acids.

• Fatty acids are important sources of fuel because, when metabolized, they yield large quantities of ATP.

• They are either saturated or unsaturated.• The saturated acids have higher melting

points than unsaturated acids of corresponding size

Soap• Fatty acids are the main component of soap, where

- their tails (hydrophobic) are soluble in oily dirt. - their heads (hydrophilic) are soluble in water.

to emulsify and wash away the oily dirt.

Types of fatty acids1. Saturated fatty acids have only single bonds.

Fats, which are mostly from animals, all saturated. 

The hydrocarbon chains in these fatty acids are, thus, fairly straight and can pack closely together, making these fats solid at room temperature.

2. Unsaturated fatty acids have one or more double bonds between carbons atoms can occur in a Cis or Trans configuration.

• Oils, mostly from plant sources, have some double bonds between some of the carbons, causing bends or “kinks” in the shape of the molecules.

• Because of the kinks in the hydrocarbon tails, these fatty acids can’t pack as closely together, making them liquid at room temperature.

• In unsaturated fatty acids , there are two ways the pieces of the hydrocarbon tail can be arranged around a C=C double bond.

• Cis bonds, the two pieces of the carbon chain on either side of the double bond are either both “up” or both “down,” such that both are on the same side of the molecule.

 • Trans bonds, the two pieces of the molecule are on opposite

sides of the double bond, that is, one “up” and one “down” across from each other.

Cis and Trans

• Naturally-occurring unsaturated vegetable oils have almost all Cis bonds, but using oil for frying converts some of the Cis bonds to Trans bonds.

• If oil is used only once like when you fry an egg, only a few of the bonds do this so it’s not too bad. However, if oil is constantly reused, like in fast food “French fries” machines, more and more of the Cis bonds are changed to Trans until significant numbers of fatty acids with trans bonds build up. The reason for this concern is that fatty acids with Trans bonds are carcinogenic, or cancer-causing.

Some exception

Although most vegetable oils are liquid at ordinary temperatures and most animal fats are solid, there are notable exceptions

- Cocoa butter, which is a solid vegetable oil.- Cod liver oil, which is a liquid animal fat. The terms saturated, mono-unsaturated, and poly-unsaturated refer to the number of hydrogens attached to the hydrocarbon tails of the fatty acids as compared to the number of double bonds between carbon atoms in the tail.

Production of Fixed Oils and Fats

original methods

by expression of the plant yielding oil by hydraulic

press mechanism

If the expression is carried

out in the cold, the oil is

known as a "virgin oil" or

a "cold-pressed oil."

current methods

by using organic solvent

Uses of Fixed Oils and Fats1-oil is a solvent for intramuscular injections.

2- it is used in the preparations of cosmetics.

3- making soaps.

4-used in the preparation of liniments, plasters

and ointments.

5- used in the manufacture dietary supplement.

6-paints and varnishes.

7-Therapeutic uses:

Safflower oil: Treatment of atherosclerosis.

Waxes• Are esters of fatty acids and a long-chain, high-molecular weight

alcohol.• Waxes is found in both animals and plants .

animals plants

produced by insects

covering the external parts, like the epidermis of leaves and fruits, where their main function is to prevent the loss of water. (Cuticle)

Beeswax - produced by honey bees

1-Soy wax - from soybean oil.2-Bayberry wax - from the surface wax of the fruits of the bayberry shrub.3-Castor wax - catalytically hydrogenated castor oil.

Application of waxes:1-Making candles ,chewing gum and polishes.2- cosmetics: -component of ointments -pastes -creams -lipsticks3-pharmaceuticals: - surface protection -glazing agent -release retardant in drugs

General differences between Waxes & fixed oils and fats

fats and oils waxfats and oils are made from

glycerol and three fatty acids joined by dehydration

synthesis 

waxes are low melting point solids and have long

alcohols chain 

Fats and oils maybe saponified by means of

either aqueous or alcoholic alkali

waxes are only saponified by alcoholic alkali.

Reference:

• http://wiki.answers.com• http://www.rawfoodexplained.com/fats/how-the-body-uses-f

at.html• http://en.wikipedia.org/wiki/Triglyceride• http://www.citycollegiate.com/biochemistry5.htm• http://en.wikipedia.org/wiki/Lipid• http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/lip

ids.htm• http://en.wikipedia.org/wiki/Fatty_acids• http://www.wax.org/wax1/pages/f_appli.htm