Beta-oxidation breaks down fatty acids into acetyl-CoA for energy. Malonyl-CoA regulates the process by controlling the transport of fatty acyl-CoA into the mitochondria. Four reactions repeat until the final products are two molecules of acetyl-CoA. Unsaturated fatty acids require an additional step to convert the double bond from cis to trans.
Beta-oxidation is a metabolic process by which fatty acids are broken down into acetyl-CoA. There are four reactions in the process and these reactions repeat until the entire fatty acid chain has been converted into single acetyl-CoA molecules. Each of these molecules is then processed to produce energy. This process takes place in the mitochondria of the cell.
Molecules involved in beta-oxidation include the fatty acid chain and coenzyme A. Coenzyme A reacts with the fatty acid chain to produce fatty acyl-CoA. The fatty acid chain is now activated and ready to be processed.
Beta oxidation is regulated by malonyl-CoA. This is an enzyme that prevents fatty acyl-CoA from entering the mitochondria. By controlling the molecules carrying fatty acyl-coA in the mitochondria, beta oxidation can be started or stopped. When more energy is needed, malonyl-CoA usually enables the transport of fatty acyl-CoA into the mitochondria. The molecule that malonyl-CoA targets is called carnitine acyltransferase.
The first beta-oxidation reaction uses the enzyme acyl-CoA dehydrogenase. This is actually made up of three enzymes that are incorporated into the mitochondrial matrix and each have a FAD molecule. Enzymes oxidize the activated fatty acid chain, while FAD is reduced. This means that one hydrogen molecule is transferred to FAD to produce FADH2.
Subsequently, another reaction catalyzed by the enzyme enoyl-CoA hydratase takes place. In this reaction, water is added to the fatty acid chain to produce hydroacyl-CoA. This is the second beta-oxidation reaction.
The third reaction involves the enzyme L-hydroxyacyl-CoA dehydrogenase. Contains the coenzyme NAD+. In this step, a beta-ketoacyl-CoA derivative is produced from the oxidation of hydroacyl-CoA. During the process, NAD+ is converted to NADH.
In the last step of this process, thiolase is the enzyme that is used. It cuts beta-ketoacyl-CoA into an acetyl-CoA molecule and a fatty acid chain that is reduced by two carbon atoms. The acetyl-CoA molecule is the end product of beta oxidation and the remaining fatty acid chain again undergoes the same four reactions. The process will repeat until the two final products are two molecules of acetyl-CoA.
For unsaturated fatty acids, i.e. fatty acids with a single double bond, beta oxidation normally occurs until the enzymes reach the double bond. Enoyl-CoA isomerase then converts the double bond from cis to trans and beta oxidation continues. Cis and trans describe the orientation of the double bond.
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