The energy of oxidation

If this energy is positive, the material is stable if negative, it will oxidise. The bar-chart of Fig. 21.1 shows the energies of oxide formation for our four categories of materials numerical values are given in Table 21.1. 

Figure 23.3 shows the voltage differences that would just stop various metals oxidising in aerated water. As we should expect, the information in the figure is similar to that in our previous bar-chart (see Chapter 21) for the energies of oxidation. There are some differences in ranking, however, due to the differences between the detailed reactions that go on in dry and wet oxidation. 

In many organisms, a central energy-conserving process is the stepwise oxidation of glucose to C02, in which some of the energy of oxidation is conserved in ATP as electrons are passed to 02. 

The next step is another oxidative decarboxylation, in which a-ketoglutarate is converted to succinyl-CoA and C02 by the action of the a-ketoglutarate dehydrogenase complex NAD+ serves as electron acceptor and CoA as the carrier of the succinyl group. The energy of oxidation of a-ketoglutarate is conserved in the formation of the thioester bond of succinyl-CoA ... 

The citric acid cycle (Krebs cycle, TCA cycle) is a nearly universal central catabolic pathway in which compounds derived from the breakdown of carbohydrates, fats, and proteins are oxidized to C02, with most of the energy of oxidation temporarily held in the electron carriers FADH2 and NADH. During aerobic metabolism, these electrons are transferred to 02 and the energy of electron flow is trapped as ATP. 

As a result of this short-circuiting of protons, the energy of oxidation is not conserved by ATP formation but is dissipated as heat, which contributes to maintaining the body temperature of the newborn. Hibernating animals also depend on uncoupled mitochondria of brown fat to generate heat during their long dormancy (see Box 17-1). 

The energy of oxidation is initially trapped as a high-energy phosphate compound and then used to form ATP. The oxidation energy of a carbon atom is hansformed into phosphoryl transfer potenhal, first as 1,3-bisphosphogly cerate and ultimately as ATP. We will consider these reachons in mechanishc detail in Sechon 16.1.5. 

The energy of oxidation is given by the redox potential of the reaction. If a piece of copper wire is placed in a solution of zinc sulfate, nothing happens, but if zinc metal is placed in a solution of copper sulfate, the zinc metal is corroded. Simultaneously, the blue color of the copper sulfate solution disappears, and metallic copper is deposited on the surface of the remaining zinc metal ... 

The rich potential for harnessing the energy of oxidation of fatty acids is realised in the mitochondria. This will be discussed in detail in Topic 20, but first we must consider how the fatty acids get there. Just as with carbohydrates, there are two issues to consider - fatty acids derived directly from our food and fatty acids derived from fat stores in adipose tissue . 

To determine the contribution of charges within the protein to the energy of oxidation/reduction the electrostatic potential is calculated in the absence of charges on the cofactors (O). The AG for the change in partial charge at each atom of the cofactor that occurs on oxidation/reduction (Aq(i)) can be calculated given the potential at that atom (4>(i)) by ... 

Further investigation led Pinchot to outline the individual steps of oxidative phosphorylation at Site I as they are presented in Fig. 1-21. In this sequence of reactions, the energy of oxidation, which has been transferred to NADH, is subsequently transferred to the NADH-enzyme complex, from there to the Pj-enzyme complex, and finally to ATP. The mode of attachment of the NADH or the phosphorus to the coupling enzyme is not known, but a histidine residue may be involved in the phosphorylation of the enzyme. 

The autotrophic bacteria are chimiosynthetic, that is, they synthesize sugars using the energy of oxidation of a constituent of the anrmimding medium. 

R. A. Marcus. On the energy of oxidation-reduction reactions involving electron transfer. 

The analogy cannot, however, be extended much beyond this. While in technology the oxidation of carbon to CO 2 is still the most important source of energy, the same process assumes a rather subordinate role in biochemistry. Furthermore, one characteristic feature of combustion processes is a drastic rise in temperature and an unchecked evolution of heat. In the mammalian body, in contrast, all processes proceed at a constant temperature (around 37 C) and the energy of oxidation appears only in part as heat, the remainder being conserved as chemical energy. 

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