Lipids are quite differing from other bio molecules like carbohydrates, proteins and nucleic acids which are polymeric in nature.
Lipid is a class of compounds included phospholipids, sterols, wax and triglycerides. The common components of all these compounds are glycerol and fatty acids.
Glycerol is a trihydric alcohol with two primary alcoholic groups and one secondary alcoholic group. Other component, fatty acids belongs to the group of carboxylic acids. The organic compounds which have carboxyl group (-COOH) are called as carboxylic acid with the general formula RCOOH, where R can be alkyl or aryl group.
If R group in carboxylic acids is long aliphatic hydrocarbon chain, it termed as fatty acid which present in lipids. Fatty acids act as a good source of energy as they can provide twice amount of energy compared to carbohydrates. That is the reason, heart and skeletal muscles use fatty acids as fuel while brain cell cannot use that and prefer to use glucose and other sources.
In general, naturally occurring fatty acids have 4-30 carbon atoms in aliphatic chain. Fatty acids can be saturated and unsaturated in nature due to the presence of double bonds.
||Number of carbon atoms
||Number of double bonds
| Butyric acid
| Caproic acid
| Caprylic acid
| Lauric acid
|| Dodecanoic acid
|| coconut oil
| Myristic acid
|| tetradecanoic acid
|| palm kernel oil
| Palmitic acid
|| hexadecanoic acid
|| palm oil
| Stearic acid
|| octadecanoic acid
|| animal fats
| Oleic acid
|| 1||9-octadeccenoic acid
|| olive oil
| Linoleic acid
|| 9,12-octadecadienoic acid
|| grape seed oil
| Gadoleic acid
|| 9-eicosenoic acid
|| fish oil
|| 5,8,11,14,17-eicosapentaenoic acid
|| fish oil
| Erucic acid
|| 13-docosenoic acis
|| raeseed oil
|| 4,7,10,13,16,19-docosahexaenoic acid
|| fish oil
| Liqnoceric acid
|| tetracosanoic acid
||small amounts in most fats
- The presence of double bonds in fatty acid prevents the free rotation in molecule and creates two configurations, cis and trans which are called as configurational isomers or geometrical isomers.
Cis-fatty acids are generally found naturally while trans-fatty acids are rare and manufactured fats which created during a process called hydrogenation of polyunsaturated fatty acids.
- Hydrogenation of polyunsaturated fatty acids stabilizing them and prevent them from becoming rancid and to keep them solid at room temperature.
For example, oxidation of arachidonic acid produced many oxidized lipids, thus for preventing the rancidity arachidonic acid can be converted into four trans isomers.
Generally, trans fatty acids added in our diet through the processed food that partially hydrogenates or we could say add hydrogen into the chain of unsaturated fatty acids and convert these into saturated fatty acids. The main advantage of trans fatty acids is their solid nature and stability due to hydrogenation which otherwise tend to turn rancid rather quickly.
No doubt trans fats derived from the more healthy vegetable oils which are saturated in nature, but they are not as much healthy as saturated one. Ingestion of trans fats increases the risk of certain cancers and dangerous for heart.
Trans fats increase total cholesterol levels and LDL cholesterol levels in body while they reduce HDL cholesterol levels. High-fat baked goods, margarines, deep-fried foods contain high concentration of trans fatty acids.
Saturated fatty acids do not have double bonds in aliphatic hydrocarbon chain while unsaturated fatty acids contain one or more double bond in carbon chain. Fatty acids with more than one double bond are called as polyunsaturated fatty acids (PUFAs). The amount of unsaturation affects the physical and chemical properties of fatty acids.
For example, saturated fatty acids are rigid and solid under normal temperature and unsaturated fatty acids exhibit the fluid nature and structure and are mostly found to be liquid at room temperature.
The catalytic hydrogenation of unsaturated fatty acids form saturated fatty acids. Some common examples of fatty acids are as follow.
|| Saturated fatty acid with C6
|| Saturated fatty acid with C12
|| Saturated fatty acid with C18
|| Unsaturated fatty acid with C14 and one double bond
|| Unsaturated fatty acid with C16 and one double bond
|| Unsaturated fatty acid with C18 and one double bond
|| Polyunsaturated fatty acid with C18 and two double bonds
|| Polyunsaturated fatty acid with C20 and four double bonds
Because of the presence of doubles bond in aliphatic hydrocarbon chain of unsaturated fatty acids, they can exhibit geometrical isomerism also called as cis-trans isomerization. Naturally occurring fatty acid exhibit cis-configuration which can be modified to artificial configuration known as trans.
In cis-form the hydrogen atoms of double bonded carbon atom oriented on same side, however in trans form they oriented in opposite direction. The differences in geometry of trans and cis-unsaturated fatty acids play an important role in biological processes.
For example, Oleic acid [CH3(CH2)7CH=CH(CH2)7COOH)] has one double bond and can exhibit cis-trans isomers. The trans-form is also named as elaidic acid.
Cis and trans forms of fatty acids show different physical and chemical properties just like other organic geometrical isomers. Trans isomers show high melting points due to closely packed structure compare to cis isomers. The configuration of unsaturated fatty acids not only affects their physical properties but also their health implications.
Consumption of trans-fatty acids is not much safe as it can be responsible for cardiovascular disease. Another issue is the resemblance of trans-fatty acid with saturated fatty acids in their structure which can interrupt many biochemical reactions.
Some other differences between cis and trans-fatty acids are as follows.
||Cis fatty acids
||Trans fatty acids
||Detrimental; lowers good cholesterol and increases the level of bad cholesterol in the body
||very less, hence produced artificially by partial hydrogenation of polyunsaturated fatty acids.
|Orientation at double bondedcarbon atoms
|| Hydrogen atoms at double bonded carbon atoms on same side
||Hydrogen atoms at double bonded carbon atoms on opposite side
||Can consume as per requirment
||No more that 1% of total calories per day
|Commonly found in
|| Natural fatty acids
|| Processes food, fast foods, butter and milky products.
| Melting point