Chapter 23.3, Problem 15SSC

Interpretation Introduction

Interpretation:

The two reactions that fatty acids undergo should be identified.

Concept introduction:

The building blocks of fat in our bodies and food are known as fatty acids. Fatty acids consist of carboxylic acids with a long aliphatic chain which can be saturated or unsaturated.

Answer to Problem 15SSC

The two reactions that fatty acids undergo are alpha-oxidation and beta-oxidation.

Explanation of Solution

Fatty acids consist of carboxylic acids with a long aliphatic chain which can be saturated or unsaturated. Generally, fatty acids exist as phospholipids, triglycerides and cholesteryl esters. These are important structural components for cells.

The two reactions that fatty acids undergo are alpha-oxidation and beta-oxidation.

Beta-oxidation: The beta-oxidation of fatty acids takes place by the removal of two carbons at a time to form acetyl-CoA. The $\beta -$ carbon of the fatty acid undergoes oxidation and results in the formation of the carbonyl group.

The overall reaction is:

Fatty acid CoA + NAD++ FAD $\to$ acetyl CoA + NADH + H++ FADH₂ The overall process consists of four steps:

1. Dehydrogenation: A long chain of fatty acid gets dehydrogenated to form a double bond between the second carbon and third carbon of the chain. Catalyzes takes place acyl CoA to produce trans ${\Delta }^2$ -Enoyl CoA.
2. Hydration: Trans ${\Delta }^2$ -Enoyl CoA gets hydrated at the double bond to form L-isomer.
3. Oxidation: Oxidation of L-isomer takes place in the presence of NAD+to convert the hydroxyl group to the keto group.
4. Thiolysis: This is the last step of the reaction where cleavage between second carbon and third carbon takes place which results in the formation of acetyl CoA.

Alpha-oxidation: The alpha-oxidation of fatty acids (presence of methyl group at $\beta -$ carbon) takes place by the elimination of one carbon atom which is located adjacent to the alpha carbon from the carboxylic acid. The alpha oxidation takes place in those fatty acids which consist of a methyl group at beta carbon (beta-oxidation can't take place).