Fatty acid degradation occurs when fatty acids are taken apart in order to produce energy. The process ultimately forms acetyl-coA and feeds it into the citric acid cycle. The whole process is broken down into three stages: lipolysis, activation and beta-oxidation. The fatty acid is broken down into its metabolites to produce energy and adenosine triphosphate (ATP).
There are both saturated and unsaturated fatty acids. An unsaturated acid has one or more double or triple bonds between carbon atoms. A saturated acid has only single bonds between its carbon atoms.
Fatty acids form part of the carboxylic acid group and are stored in adipose tissues. They enter the body through intestinal capillaries or vili. Glucose and fatty acids are the two main sources of energy in the body, although the brain cannot process fatty acids.
The first stage of fatty acid degradation is called lipolysis. The fatty acids are stored in cells called adipocytes and are first broken down into free fatty acids so they can enter the blood system. Lipolysis is induced by a number of hormones including norepinephrine and testosterone. Apart from free fatty acids, glycerol is produced as a byproduct.
Activation takes place before the fatty acid is take into a cell’s mitochondria. First, an enzyme called Acyl-CoA Synthetase induces a nucleophilic attack on the alpha-phosphate of ATP, which creates an acyl chain linked to adenosine monophosphate (AMP) and a pyrophosphate. The enzyme then forms an activated thioester bond between Coenzyme A and the acyl chain. The fatty acid is then transported into the mitochondrion using the carnitie carrier system.
Beta-oxidation is the final phase of fatty acid degradation and a takes place in four stages. First, the fatty acid is dehydrated using Flavin Adenine Dinucleotide (FAD). Second, the bonds between the second and third carbons are hydrated. Third, Nicotinamide Adenine Dinucleotide (NAD) is used to oxidate the molecule. In the last step, beta-keroacyl is added during thiolysis to a second CoA molecule placed between the second and third carbons.
The final product of the three stages of fatty acid degradation is Acetyl-CoA. This is a metabolism molecule used to carry carbon atoms. The molecule is then fed into the citric acid cycle, an essential part of energy supply.
The citric acid cycle is a series of chemical reactions using oxygen or the products of fatty acid degradation. The entire cycle takes place within the mitochondrion of eukaryotic cells or within the cytoplasm of prokaryotes. Carbon dioxide is a byproduct of the energy-producing process. Fatty acids pass through the system once, but glucose needs to be processed twice in order to reap all its energy.