Phospholipid Structure

• Phospholipids consist of a backbone of glycerol or sphingosine connected to fatty acids, a phosphate group, and other molecules that vary with the type of phospholipid. They are amphipathic, meaning that each of their molecules has a hydrophilic (water-loving) head and a long, hydrophobic (water-insoluble) tail. Thus, phospholipids can dissolve in both water and oil.
  
  

Cholesterol Structure

• Cholesterol is a highly hydrophobic compound. Its central core of four fused hydrocarbon rings is a common component of all steroid hormones. According to "Lippincott's Illustrated Reviews: Biochemistry," most blood cholesterol exists in an esterified form--that is, with an attached fatty acid.
  
  

Transport

• The American Heart Association indicates that large molecules named lipoproteins act as transporters of phospholipids and cholesterol in the bloodstream. The five major families of blood lipoproteins are chylomicrons, very low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), low-density lipoproteins (LDL) and high-density lipoproteins (HDL). The terms "good cholesterol" and "bad cholesterol" generally refer to HDL cholesterol and LDL cholesterol, respectively.
  
  

Sources

• Virtually all cells, except mature red blood cells, can produce phospholipids. They produce phospholipids through a process called synthesis, in which two or more simple compounds are combined to form a complex compound. According to data from the University of Cincinnati, the body typically produces 85 percent of the cholesterol it needs each day. It synthesizes most of this cholesterol in the liver, intestines, adrenal glands, and reproductive organs. Dietary sources account for about 15 percent of blood cholesterol levels.
  
  

Functions

• Phospholipids and cholesterol act as essential structural components of all cell membranes. Phospholipids also act as components of bile and lung surfactant (a tension-reducing substance lining the lungs), as anchors for other membrane proteins and as a reservoir for messenger molecules. Cholesterol is necessary for the production of bile acids, steroid hormones, and vitamin D.
  
  

Famous Phospholipid

• Lecithin, a well-known phospholipid, is available as a dietary supplement. Like cholesterol, it exists naturally in many foods, such as egg yolks and meat. Nutros.com notes that lecithin's ability to mix water and oil forms the basis of mayonnaise.