Question

Another minor pathway of fatty acid oxidation is \(\omega\) -oxidation, which results in a hydroxylation. \(\omega\) -Oxidation A. occurs in mitochondria. B. introduces the \(-\mathrm{OH}\) on the carbon adjacent to the carboxyl group. C. oxidizes primarily very long-chain fatty acids. D. oxidizes the terminal methyl group. E. produces dicarboxylic acids in the initial oxidation.

Short answer

Answer: ω-oxidation oxidizes the terminal methyl group on fatty acids.

Step-by-step solution

Identify the correct statement about ω-oxidation of fatty acids

To answer this question, we need to go through each statement and determine whether it is true or false based on our understanding of ω-oxidation. A. occurs in mitochondria: Although fatty acid oxidation generally occurs in the mitochondria, ω-oxidation primarily takes place in the endoplasmic reticulum. B. introduces the \(-\mathrm{OH}\) on the carbon adjacent to the carboxyl group: In ω-oxidation, the hydroxylation (\(-\mathrm{OH}\)) occurs on the terminal (ω) carbon, not the carbon adjacent to the carboxyl group. C. oxidizes primarily very long-chain fatty acids: ω-oxidation primarily oxidizes medium-chain fatty acids, while the peroxisomal β-oxidation pathway is more common for very long-chain fatty acids. D. oxidizes the terminal methyl group: This statement is true. ω-oxidation involves the oxidation of the terminal methyl group on the fatty acid. E. produces dicarboxylic acids in the initial oxidation: Dicarboxylic acids are not produced in the initial oxidation of ω-oxidation. They are formed only after the fatty acid has gone through several oxidation steps. Based on our evaluation of the answer choices, we can see that option D is the correct answer. ω-oxidation oxidizes the terminal methyl group on fatty acids.

Key concepts

Fatty Acid Metabolism

Fatty acid metabolism is a vital biochemical process involving the breakdown and synthesis of fatty acids within our bodies. It plays an essential role in energy production and storage, cellular signaling, and the formation of cell membranes.

Within the catabolic pathways of fatty acid metabolism, β-oxidation is most well-known, where fatty acids break down inside mitochondria to generate acetyl-CoA, which further enters the citric acid cycle for ATP production. However, lesser-known pathways such as ω-oxidation also exist. Unlike the common β-oxidation pathway, ω-oxidation involves the modification of the terminal methyl group on fatty acids, specifically by adding a hydroxyl group (-OH), primarily within the endoplasmic reticulum, not the mitochondria.

This process of ω-oxidation acts as an alternative metabolic route, particularly when β-oxidation is impaired or when specific types of fatty acids, such as medium-chain fatty acids, need to be processed.

Endoplasmic Reticulum

The endoplasmic reticulum (ER) is an extensive network of membranes within eukaryotic cells that plays a multifaceted role in the synthesis, folding, modification, and transport of proteins and lipids.

Concerning fatty acid metabolism, the ER is the primary site for lipid synthesis and the ω-oxidation of fatty acids. This alternative oxidation pathway begins with the oxidation of the last carbon of the fatty acid chain, known as the terminal methyl group oxidation. Enzymes embedded in the ER's membranes facilitate this process, an illustration of the ER's role in cellular metabolism beyond protein synthesis.

Understanding the functions of the ER is crucial in grasping metabolic pathways, especially the ω-oxidation of fatty acids which does not occur in the mitochondria, contrary to what might be assumed given the central role of mitochondria in energy metabolism.

Medium-Chain Fatty Acids

Medium-chain fatty acids (MCFAs) are fatty acids with a length ranging from 6 to 12 carbon atoms. They are distinct from long-chain and very long-chain fatty acids in both their physical properties and metabolic fate.

MCFAs are commonly found in various dietary fats, including coconut oil and palm kernel oil. Metabolically, MCFAs are easily absorbed and directly transported to the liver, where they are rapidly oxidized for energy. In the context of ω-oxidation, the ER preferentially processes MCFAs, which is significant as this pathway serves as a supplementary route to β-oxidation for medium-chain fatty acids, becoming especially relevant when β-oxidation is compromised.

Terminal Methyl Group Oxidation

Terminal methyl group oxidation refers to the oxidation of the terminal, or omega (ω), carbon of a fatty acid. This contrasts with β-oxidation, where oxidation begins at the β carbon, two carbons away from the acid group.

In ω-oxidation, the terminal carbon (farthest from the carboxyl group of fatty acids) is hydroxylated to form a new hydroxy fatty acid. Initially, an alcohol group is introduced, followed by the conversion into a carboxylic acid, thus giving rise to fatty acids with both terminal and sub-terminal carboxylic groups. This unique pathway serves as a minor route of fatty acid catabolism but can have increased significance under certain physiological conditions or in the metabolism of xenobiotics and drugs.