MoBio Phospholipids Chapter 1

A phospholipid consists of a hydrophilic polar head group and a hydrophobic tail. The polar head group contains one or more phosphate groups (PO43-). 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.


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.

Chemical Formula Name
Saturated fatty acid  
CH3(CH2)10COOH Lauric
CH3(CH2)12COOH Myristic
CH3(CH2)14COOH Palmitic
CH3(CH2)16COOH Stearic
CH3(CH2)18COOH Arachidic
CH3(CH2)22COOH Lignoceric
Unsaturated fatty acid  
CH3(CH2)5CH=CH(CH2)7COOH Palmitoleic
CH3(CH2)7CH=CH(CH2)7COOH Oleic
CH3(CH2)4(CH=CHCH2)3CH=CH(CH2)3COOH Arachidonic

Note: In the bond-line representation,

Palmitic acid (saturated) is represented as


Arachidonic acid (unsaturated) is represented as