Lipid Pathways

Lipid Pathways

Although foods may contain lipids in the form of phospholipids or cholesterol, the most common dietary lipids are fats. A molecule of such a lipid consists of a glycerol portion and 3 fatty acids and is called a triglyceride. 

The metabolism of lipids is controlled mainly by the liver, which can remove them from the circulating blood and alter their molecular structures For example, the liver can shorten or lengthen the carbon chains of fatty acid molecules or introduce double bonds into these chains, thus converting fatty acids from one form to another Lipids provide for a variety of physiological functions, however, they are used mainly to supply energy Fats are a particularly concentrated form of energy because gram for gram, they contain more than twice as much chemical energy as carbohydrates or proteins.
 

Before energy can be released from a triglyceride molecule it must undergo hydrolysis. Some of the resulting fatty acid portions can then be converted into molecules of acetyl coenzyme A by a series of reactions called beta oxidation. In these reactions, fatty acid molecules are broken down by mitochondria into segments containing 2 carbon atoms each. 

Lipid metabolism pathway

Some of these segments are converted into acetyl coenzyme. A molecule, Other segments are converted into compounds called ketone bodies, which later may be changed to acetyl coenzyme A. 

In either case. the resulting acetyl coenzyme A can be oxidized by means of the citric acid cycle. The glycerol portions of the triglyceride molecules can also enter metabolic pathways leading to the citric acid cycle, or they can be used to synthesize glucose.

Another possibility for glycerol and fatty acid molecules resulting from the hydrolysis of fats is to be changed back into fat molecules by anabolic processes and stored in fat tissue. Additional fat molecules can be synthesized from excess molecules of glucose or amino acids.