BIOLOGY Volume 1 - A Guide to General Biology - 2004

3. CHEMICAL COMPONENTS OF LIVING MATTER

3.3. Lipids

3.3.4. Phospholipids

Phospholipids are Lipids that contain a phosphate group. The most prominent among them are phosphoglycerides, in which one of the three —OH groups of glycerol is esterified with phosphoric acid rather than a fatty acid (Fig. 3.18), while the other two are esterified with Fatty acids.

A molecule consists of a HEAD, formed by the phosphate group (represented by the circle in Fig. 3.18), and two hydrocarbon tails (fatty acid residues). The phosphate head carries an electrical charge and is therefore soluble in Water; in other words, it is hydrophilic. The tail, by contrast, is insoluble in water. This dual property of the molecule—where one end is water-soluble while the other is not—plays a crucial role in membrane formation (Section 5.9).

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Fig. 3.18. Formation of a phospholipid. In simplified terms, the molecule can be represented as a head with two tails. The highly polar phosphate head is hydrophilic, unlike the non-polar and therefore hydrophobic tails. This feature is of great biological significance as it dictates The properties of membranes.



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