Cholesterol

Lipids

Lipids are a diverse group of naturally occurring fat-soluble molecules, with biological functions that include acting as structural components of cell membranes, energy storage sources and intermediates in signalling pathways. Lipids can be divided into two main groups, simple and complex. The two most important simple lipids are cholesterol and fatty acids. Lipids become complex when fatty acids undergo esterification to produce esters.¹

Simple lipids:
Cholesterol is a soft waxy substance present in all cells of the body. Most tissues can produce cholesterol, but it is synthesised primarily in the liver and small intestine. Approximately half of the body’s cholesterol requirement is synthesised, while the rest is obtained through animal products in the diet. Cholesterol is important in the repair of cell membranes and the synthesis of steroid hormones, vitamin D and bile acids. Fatty acids are the simplest form of lipid found in the body and are an important energy source. They exist as saturated, monounsaturated and polyunsaturated forms, distinguished by the number of bonds between carbon atoms in the hydrocarbon chain.¹

Complex lipids:
Triglycerides are the storage molecules of fatty acids in the adipose tissue, and play an important role in transporting fatty acids around the body. Phospholipids are glycerol esters containing two fatty acids, and are an important component of cell membranes. Cholesterol esters are the storage molecules of cholesterol in cells.¹

In order for water-insoluble lipids to be transported around the body in the bloodstream, they are aggregated with apolipoproteins to form lipoproteins. These multimolecular packages consist of a hydrophobic core containing cholesteryl esters and triglyceride, surrounded by a hydrophilic surface layer of phospholipids, proteins and some free cholesterol.¹

Reference:
1. In: Fast Facts - Hyperlipidaemia. Eds Durrington P, Sniderman A. Health Press Ltd, Oxford, 2000. 1-17.