Phospholipids

A phospholipid molecule consists of a hydrophilic polar head group and a hydrophobic tail.  The polar head group contains one or more phosphate groups.  The hydrophobic tail is made up of two fatty acyl chains.  When many phospholipid molecules are placed in water, their hydrophilic heads tend to face water and the hydrophobic tails are forced to stick together, forming a bilayer.

(a)

(b)

Figure 1-B-2.  Structure of a phospholipid (phosphatidylcholine). (a) Chemical structure. (b) A computer model.

Polar head groups:

Most phospholipid head groups belong to phosphoglycerides, which contain glycerol joining the head and the tail.  Examples of phosphoglycerides include phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, phosphatidylinositol, etc.

Fatty acyl chains:

The fatty acyl chain in biomembranes usually contains even number of carbon atoms. They may be saturated (neighboring C atoms are all connected by single bonds) or unsaturated (some neighboring C atoms are connected by double bonds). 

Table 1-B-1.  Cellular fatty acids.

    
Note: In the bond-line representation,

Palmitic acid is represented as

Arachidonic acid is represented as

Review Articles:

The Biochemistry of n-3 Polyunsaturated Fatty Acids - J. Biol. Chem., 2001.

Sphingolipid Metabolism and Signaling - J. Biol. Chem., 2002.

• Introduction
• De Novo Sphingolipid Biosynthesis: A Necessary, but Dangerous, Pathway
• The Ceramide-centric Universe of Lipid-mediated Cell Regulation: Stress Encounters of the Lipid Kind
• Sphingosine 1-Phosphate, a Key Cell Signaling Molecule
• Sphingolipid Transport: Rafts and Translocators
• Combinatorial Ganglioside Biosynthesis