Loading....
Coupon Accepted Successfully!

 

Lipids

 The lipids are heterogenous group of compounds related by their physical rather than by their chemical properties. They have the common property of being (1) relatively insoluble in water and (2) soluble in nonpolar solvents such as ether, chloroform and benzene.

A.   Classification of Lipids

  1. Simple lipids: Esters of fatty acids with various alcohols.
    1. Fats: Esters of fatty acids with glycerol. A fat in the liquid state is known as oil.
    2. Waxes: Esters of fatty acids with higher molecular weight monohydric alcohols.

2. Complex lipids: Esters of fatty acids containing groups in addition to an alcohol and fatty acids.

  1. Phospholipids: Lipids containing fatty acid, alcohol and a phosphoric acid residue. Eg. glycerophospholipids and sphingophospholipids.
  2. Glycolipids: Lipid containing a fatty acid, sphingosine and carbohydrates.
  3. Other Complex Lipids: for eg. sulfolipids, aminolipids and lipoproteins.

3. Precursor and derived lipids: These include fatty acids, glycerol, steroids, alcohol etc.

 

B. Fatty Acids

Fatty acids are water-insoluble, saturated or unsaturated long-chain hydrocarbon with a carboxyl group at the end of the chain.

  1. Saturated fatty acids do not contain double bond in the chain.
  2. Unsaturated fatty acids have one or more double bond. (In naturally occurring fatty acids, these bonds are always in cis configuration)
    1. Numbering system : Carbon atoms are numbered from the carboxyl carbon (carbon no. 1). The carbon adjacent to carboxyl carbon (No. 2) is also known as α-carbon. Carbon atom no. 3 and 4 are the ââ and γ carbon respectively and the terminal methyl carbon is known as ω-carbon.
    2. The systematic name gives the number of carbon atoms, number of double bonds and position of double bonds by delta (Δ) numbering system and bear the suffix –enoic.

The various important unsaturated fatty acids of physiological important are as below:

 

Table. Unsaturated Fatty Acids of Physiologic and Nutritional Significance.

 

Number of C Atoms and Number and Position of Double Bonds

Family

Common Name

Systematic Name

Occurrence

Monoenoic acids (one double bond)

16:1;9

ω7

Palmitoleic

cis-9-Hexadecenoic

In nearly all fats.

18:1;9

ω9

Oleic

cis-9-Octadecenoic

Possibly the most common fatty acid in natural fats.

18:1;9

ω9

Elaidic

trans-9-Octadecenoic

Hydrogenated and ruminant fats.

Dienoic acids (two double bonds)

18:2;9,12

ω6

Linoleic

all-cis-9,12-Octadecadienoic

Corn, peanut, cottonseed, soybean, and many plant oils.

Trienoic acids (three double bonds)

18:3;6,9,12

ω6

Gama-Linolenic

all-cis-6,9,12-Octadecatrienoic

Some plants, eg, oil of evening primrose, borage oil; minor fatty acid in animals.

18:3;9,12,15

ω3

Alpha- Linolenic

all-cis-9,12,15-Octadecatrienoic

Frequently found with linoleic acid but particularly in linseed oil.

Tetraenoic acids (four double bonds)

20:4;5,8,11,14

ω6

Arachidonic

all-cis-5,8,11,14-Eicosatetraenoic

Found in animal fats; important component of phospholipids in animals.

Pentaenoic acids (five double bonds)

20:5;5,8,11,14,17

ω3

Timnodonic

all-cis-5,8,11,14,17-Eicosapentaenoic

Important component of fish oils, e.g., cod liver, mackerel, menhaden, salmon oils.

Hexaenoic acids (six double bonds)

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

ω3

Cervonic

all-cis-4,7,10,13,16,19-Docosahexaenoic

Fish oils, phospholipids

 





Test Your Skills Now!
Take a Quiz now
Reviewer Name