General Index


Fatty Acids

Index


Fatty Acids are monocarboxylic acid with an even number of carbon atoms. The even number is due to its mode of biosynthesis, consisting in the succesive addition of -C-C- (C2) units. In fatty acid we usually distinguish between (a) The carboxyl group -COOH, that at physiological pH appears normally dissociated as -COO- and (b) the hydrocarbon chain CH3-CH2-CH2-.... This one is strongly hydrophobic, while the dissociated carboxyl interacts easily with water. This fact gives to the fatty acid a certain amphipathic character, that is, both hydrophobic and hydrophilic portions can be seen in the same molecule.

Saturated Fatty Acids

When the hydrocarbon chain contains only sp3 carbons, that is, is fully saturated, we speak of Saturated Fatty Acids. But very often appear double bonds -C=C- in the chain; we call these Unsaturated Fatty Acids. These have lower melting points than the saturated ones. This makes lipids containing saturated acids to be solid at room temperature (fats) while those rich in unsaturated acids are liquid at room temperature (oils).

The saturated acid are linear molecules, according to the alternating conformation seen in saturated hydrocarbon chains. It is convenient to use the display option spacefill to have an idea of the general shape of these molecules.



















































Index

Unsaturated Fatty Acids

The unsaturated fatty acids present double bonds, that almost invariably are of the cis- geometrical type. If there appears only one unsaturation in the molecule, we speak of Monounsaturated. If there are several, we call them Polyunsaturated. In this case , the unsaturations never appear in conjugation (-C=C-C=C-) but every three carbons (-C=C-C-C=C-).

From a structural point of view, cis-unsaturations cause an angle in the carbon chain, and thus these molecules are not straight lines as those of saturated acids. This is the cause of unsaturated acids having lower melting points than the saturated ones. In the case on polyunsaturated acids (case of linoleic, linolenic and arachidonic acids) the molecule may even adopt the form of a horseshoe. These polyunsaturated acids are essential in the human diet.


























Index

Eicosanoids

Eicosanoids are derivatives of polyunsaturated fatty acids that act as local chemical signals.

There are three classes of eicosanoids: Prostaglandins, Thromboxanes. and Leukotrienes. We present some representative structures of these molecules:





















Index
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