Energy Yield from Fatty Acid Oxidation

Energy Yield from Fatty Acid Oxidation 

What is the total energy yield (number of ATPs) from oxidizing one molecule of palmitic acid to CO2 Palmitic acid has 16 carbons, so you can break it down into eight acetyl-CoA molecules, with the formation of one FADH2 and one NADH at each of the seven P-oxida-tion steps. Electron transport starting with FADH2 yields two ATPs and with NADH yields three ATPs. Therefore, P-oxidation yields the equivalent of 35 ATPs per molecule of palmitic acid. Each acetyl-CoA goes into the TCA cycle, where its metabolism yields three NADHs, one FAD, and one GTP directly, for a total of 12 ATPs. Thus, the ATPs produced are  

Two ATP equivalents were used to activate the fatty acid, leading to a total energy yield of 129 ATPs, over three times the amount of energy obtained from metabolizing a single molecule of glucose. 

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Energy yield from fatty acid oxidation The energy yield from ihe P-oxidation pathway is high. For example, the oxidation of a molecule of palmitoyl CoA to C02 and H20 yields 131 AIRs (Figure 16.19). A comparison of the processes of synthesis and degradation of saturated fatty acids with an even number of car bon atoms is provided in Figure 16.20. 

Energy Yield from Fatty Acid Oxidation... 

The energy yield from fatty acid oxidation... 

In the second stage of fatty acid oxidation, the acetyl-CoA is oxidized to C02 in the citric acid cycle. A large fraction of the theoretical yield of free energy from fatty acid oxidation is recovered as ATP by oxidative phosphorylation, the final stage of the oxidative pathway. 

It is instructive to compare the energy yield from the complete oxidation of fatty acids with that obtained from an equivalent amount of glncose becanse both are important constituents of the diet. In Section 13.8, we saw that the oxidation of a single glucose molecule produces 32 ATP molecules. The complete oxidation of three 6-carbon glucose molecules... 

The higher energy yield per carbon atom from fatty acid compared with carbohydrate reflects its higher level of reduction, which consequently allows more oxidation. Thus, fat is logically the preferred storage molecule to carbohydrate. This is... 

Triacylglycerols are highly concentrated stores of metaholic energy because they are reduced and anhydrous. The yield from the complete oxidation of fatty acids is about 9 kcal g" (38 kJ g- ), in contrast with about 4 kcal g l (17 kJ g-i) for carbohydrates and proteins. The basis of this large difference in caloric yield is that fatty acids are much more reduced. Furthermore, triacylglycerols are nonpolar, and so they are stored in a nearly anhydrous form, whereas much more polar proteins and carbohydrates are more highly hydrated. In fact, 1 g of dry glycogen binds about 2 g of water. 

As an example of the energy yield from p-oxidation, the balance sheet for ATP production when the sixteen-carbon-fatty acid palmitic acid is degraded by p-oxidation is summarized in Figure 23.8. Complete oxidation of palmitate results in production of 129 molecules of ATP, three and one half times more energy than results from the complete oxidation of an equivalent amount of glucose. 

Various situations yield to induction of fatty acid catabolism in the liver such as birth which corresponds to a transition in energy source from a carbohydrate-rich to a lipid-rich regimen fasting, which is associated with free fatty acid release in the blood due to lipolysis of the adipose tissue as well as exposure to various xenobiotics. Several biochemical mechanisms exist to rapidly control the activity of the different enzymes involved in fatty acid oxidation. However, the transcriptional regulation of the expression of these enzymes is an additional level of control necessary for long-term maintenance of the organism energy balance. 

The Energy Yield from the Oxidation of Fatty Acids... 

What is the energy yield from the oxidation of fatty acids There is a net yield of 120 ATP molecules for each molecule of stearic acid (an 18-carbon compound) that is completely oxidized to carbon dioxide and water. The source of these ATP molecules is the production of NADH and LADHg in the P-oxidation pathway, as well as the NADH, LADHg, and GTP produced when the acetyl-GoA molecules are processed through the electron transport chain. 

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