Fatty Acid Metabolism
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Fatty Acid Metabolism Margaret A. Parka* and Charles Chalfanta,b a Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA, USA b Research Career Scientist, Research and Development, Hunter Holmes McGuire VAMC, Richmond, VA, USA
Synopsis Fatty acids are extremely efficient at storing energy and are used by many organisms for metabolic reactions. In this review of fatty acid metabolism, fat molecules will be followed from dietary intake and digestion, through storage and mobilization, oxidation, and finally ketone body formation. The regulation of each of these processes will also be discussed. Finally, genetic abnormalities and disorders of fatty acid oxidation will be examined. Most of the concepts in this entry will focus on the human metabolism of fatty acids. However, other species will be discussed when of relevance.
Introduction Living cells require a constant input of energy for metabolic functions and to maintain homeostasis. For most non-photosynthetic organisms, this energy is acquired from the oxidation of various food sources such as proteins, carbohydrates, and fats. Energy is derived from the breakdown of individual subunits of these substances into acetyl-CoA and the subsequent cycling of this molecule through the citric acid cycle and the mitochondrial oxidative phosphorylation pathway. ATP is thereby produced providing chemical energy for cells, thus allowing for the maintenance of homeostasis and continued normal function. Fatty acids are especially important in the production of ATP from foods and this entry will serve as an overview of these vital pathways. Fatty acids (FAs) are a diverse subgroup of lipids including straight-chain FAs, substituted FAs (fatty acids with substituents other than methyl groups), branched-chain FAs, and ring-containing fatty acids. This group of molecules has a similarly diverse range of functions including energy storage, protection from water saturation (such as the FAs found in the preening glands of birds), membrane structure, protein modification (lipoproteins), and scavenging of reactive oxygen species (tocopherols). Fatty acids can be used as subunits to build mono-, di-, and triacylglycerol molecules (see Fig. 1), the body’s main source of stored energy. Fatty acids as a group are negatively charged linear hydrocarbon chains of various lengths. The negative charge is located at a carboxyl end group that is completely deprotonated at physiological pH values. Fatty acids are especially efficient stores of energy, as these molecules can provide more than twice as much energy per gram as carbohydrates. Moreover, fatty acid molecules are easily stored in the body, and many mammals store the majority of their energy in this form in adipose tissue (reviewed in sections “Development of Adipose Tissue” and “Fatty Acid Synthesis (Lipogenesis)”). Hibernating mammals, for example, store fats as energy for use over long periods of time, thus avoiding the need for re-fueling (Kalish et al. 2012).
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