Category: Lipids

The three principal classes of lipids that form the bilayer matrix of biological membranes are glycerophospholipids, sphingolipids, and sterols (principally cholesterol). The most important characteristic of molecules in the first two groups is their amphipathic structure—well separated hydrophilic (polar) and hydrophobic (nonpolar) regions. Generally, their shape is elongated, with a hydrophilic end or head attached…

A second group of neutral lipids that are of physiological importance, though they are a minor component of biological systems, are waxes. Essentially, waxes consist of a long-chain fatty acid linked through an ester oxygen to a long-chain alcohol. These molecules are completely water-insoluble and generally solid at biological temperatures. Their strongly hydrophobic nature allows them to function as Water repellents on the…

Triglycerides are hydrophobic substances that are soluble only in some organic solvents. Unlike many other types of complex lipids, they possess no electric charges and are therefore referred to as neutral lipids. The molecular structure of a few triglycerides that have been studied in crystals indicates that the acyl chains on the 1 and 2…

Triglycerides Triglycerides (chemical name triacylglycerol), the principal means of storing fatty acids in biological systems, are a class of compounds that consist of glycerol (a three-carbon trihydroxy alcohol) with a fatty acid linked to each of the three OH groups by an ester bond. An example of a typical triglyceride is tristearin. Because this molecule contains only…

In mammals, fatty acids are synthesized in adipose and liver cells from glucose via a fairly complex pathway. In essence, the six carbons of a glucose molecule are oxidized to a pair of two-carbon carboxylic acid fragments called acetate. The starting point for biosynthesis is an acetate group chemically linked to a molecule of CoA (coenzyme A). The process of building…

After transport through the circulation, triglycerides are hydrolyzed yet again to fatty acids in the adipose tissue. There they are transported into adipose cells, where once again they are resynthesized into triglycerides and stored as droplets. Fat or adipose tissue essentially consists of cells, whereby the interior of each cell is largely occupied by a fat…

The main source of fatty acids in the diet is triglycerides, generically called fats. In humans, fat constitutes an important part of the diet, and in some countries it can contribute as much as 45 percent of energy intake. Triglycerides consist of three fatty acid molecules, each linked by an ester bond to one of the three OH groups of a glycerol molecule. After ingested…

Fatty acids are found in biological systems either as free molecules or as components of more-complex lipids. They are derived from dietary sources or produced by metabolism, as described below.

The most chemically reactive portion of fatty acids is the acidic carboxyl group (COOH). It reacts with alcohols (R′OH) to form products known as esters (RCOOR′) and releases water in the process. This ester bond is the principal covalent bond linking fatty acid moieties to other groups in the more-complex lipids discussed in other sections of this article. A second chemical bond, occurring…

Pure fatty acids form crystals that consist of stacked layers of molecules, with each layer the thickness of two extended molecules. The molecules in a layer are arranged so that the hydrophobic (water-fearing) hydrocarbon chains form the interior of the layer and the hydrophilic (water-loving) carboxylic acid groups form the two faces. For a specific fatty acid…