ID no. 430104777
section 29083
Lipids are biological molecules that are generally insoluble in water. Lipids are soluble in organic solvents, like alcohols and ethers. Their chemical composition generally consists of carbon and hydrogen atoms. Oil, butter, and wax are examples of natural substances that are mainly made of lipids [1].
Lipids are essential in animals and plants as they are [2]:
- Used to store energy and save it for time in need.
- The main material that make up biological membranes.
- Used as waterproof coverings.
In most cases, lipids form when glycerol molecules combine with fatty acids, which are organic acids that consist of a long chain of carbon atom and end with carboxyl group (COOH) [3]. If each carbon atom in the fatty acid part is joined by a single bond to the next carbon atom, then the lipid is said to be saturated. However, if a carbon-carbon double bond exists in the carbon atoms series, then the lipid becomes unsaturated. In the saturation case, the fatty acids include the maximum number of hydrogen atoms. There is a third case that exists if we have more than one carbon-carbon double bond in the carbon atom series. That case (form) is called polyunsaturated lipids [2].
We mentioned earlier that all lipids share some major distinctive characteristics. However, not all lipids are exactly the same. Lipids can be divided into different classes (forms). Usually, the side chain is the reason for lipids diversity.
TRIGLYCERIDES
There chemical form simply consists of triesters of glycerol with fatty acids which are long-chain carboxylic acids. In the nature, this structure basically describes the structure of natural fats and oils. Triglycerides are so important to living organisms as they are the long-term storage form of energy. Triglycerides form when a glycerol molecule reacts with 3 fatty acid molecules to form the triester of glycerol (Triglyceride) [4].
PHOSPHOLIPIDS
They are basically lipids that contain phosphate groups. Phospholipids are abundant in living cells. Phospholipids tend to form a head- tail structure. The head is hydrophilic (water-loving) and ionic. While the tail is hydrophobic (water-hating) hydrocarbon. Phospholipids tend to form a spherical double layer, known as lipid bilayer. In that structure, the hydrophobic tails of the phospholipids are packed between the two layers of hydrophilic heads. Phospholipids are so important to our body cells as they form the cell membrane that controls the passage of molecules and ions into and out of the cell. The following picture shows the structure of a phospholipid molecule [4].
WAXES
They are simply esters that have long chains of fatty acids and long chains of alcohols. Unlike triglycerides and phospholipids which involve a trihydric alcohol (glycerol), waxes involve a monohydric alcohol in their formation. For example, beeswax, a substance secreted by the wax glands of bees, is mainly myricyl palmitate. Myricyl palmitate is formed from the reaction of palmitic acid and carnaubyl alcohol (monohydric alcohol). Wax is the substance that covers the surface of leaves and fruits (waterproof ability). Wax also covers the skins and feathers of animals. Commercially, waxes have a great importance. They are widely used in the production of cosmetics and candles [5].
Bibliography:
[1] "Lipids definition - Medical Dictionary definitions of popular medical terms easily defined on MedTerms." Web. 01 Dec. 2009.
[2] Levine, Joseph S., and Kenneth R. Miller. Prentice Hall Biology. 2006. Print.
[3] "Fatty Acids." Microsoft® Student 2008 [DVD]. Redmond, WA: Microsoft Corporation, 2007.
[4] Wilbraham, Antony C., Dennis D. Staley, Michael S. Matta, and Edward L. Waterman. Prentice Hall Chemistry. Boston, 2008. Print.
[5] Zumdahl, Steven S., and Donald J. DeCoste. Introductory Chemistry A Foundation. Boston: Charles Hartford, 2008. Print.
