Electron transport chain and oxidative phosphorylation

The term vitamin K2 was applied to 2-methyl-3-difarnesyl-l,4-naphthoquinone, m.p. 54 C, isolated from putrefied fish meal. It now includes a group of related natural compounds ( menaquinones ), differing in the number of isoprene units in the side chain and in their degree of unsaturation. These quinones also appear to be involved in the electron transport chain and oxidative phosphorylation. 

As fuel molecules are oxidized, the electrons they have lost are used to make NADH and FADH2. The function of the electron transport chain and oxidative phosphorylation is to take electrons from these molecules and transfer them to oxygen, making ATP in the process. 

Mitochondrial diseases are often expressed as neuropathies and myopathies because brain and muscle are highly dependent on oxidative phosphorylation. Mitochondrial genes code for some of the components of the electron transport chain and oxidative phosphorylation, as well as some mitochondrial tRNA molecules. 

Figure 4-13. The electron transport chain and oxidative phosphorylation. Heavy arrows indicate the flow of electrons. Fe-S = iron-sulfur centers FMN = flavin mononucleotide CoQ = coenzyme Q (ubiquinone) Cyt = cytochrome. nH+ indicates that an undetermined number of protons are pumped from the matrix to the cytosolic side. The numbers at the top of the figure correspond to the three major stages of electron transfer described in the text in V B.

Glucose is the only fuel used by red blood cells, because they lack mitochondria. Fatty acid oxidation, amino acid oxidation, the TCA cycle, the electron transport chain, and oxidative phosphorylation (ATP generation that is dependent on oxygen... 

The TCA cycle occurs in the mitochondrion, where its flux is tightly coordinated with the rate of the electron transport chain and oxidative phosphorylation through feedback regulation that reflects the demand for ATP. The rate of the TCA cycle is increased when ATP utilization in the cell is increased through the response of several enzymes to ADP levels, the NADH/ NAD ratio, the rate of FAD(2H) oxidation or the Ccf concentration. For example, isocitrate dehydrogenase is allosterically activated by ADP. 

The citric acid cycle is considered part of aerobic metabolism because of the link to the electron transport chain and oxidative phosphorylation. NADH and FADHg generated by the citric acid cycle ultimately pass their... 

Goenzymes are introduced in this chapter and are discussed in later chapters in the context of the reactions in which they play a role. Chapter 16 discusses carbohydrates. Chapter 17 begins the overview of the metabohc pathways by discussing glycolysis. Glycogen metabolism, gluconeogenesis, and the pentose phosphate pathway (Chapter 18) provide bases for treating control mechanisms in carbohydrate metabolism. Discussion of the citric acid cycle is followed by the electron transport chain and oxidative phosphorylation in Chapters 19 and 20. The catabolic and anabolic aspects of lipid metabohsm are dealt with in Chapter 21. In Chapter 22, photosynthesis rounds out the discussion of carbohydrate metabolism. Chapter... 

When oxygen is introduced, reduced cofactors in the citric acid cycle can be reoxidized in the electron transport chain and oxidative phosphorylation occurs. Under these conditions the yeast cell can utilize glucose much more efficiently, producing 30 molecules... 

Metabolism, the sum of all cellular reactions, involves the breakdown (catabolism) and synthesis (anabolism) of molecules. Objective 6 (Section 12.6), Exercise 12.26. There are three stages in the catabolism of foods to provide energy. In Stage I, digestion converts foods into smaller molecules. In Stage II, these smaller molecules are converted into two-carbon acetyl units that combine with coenzyme A, forming acetyl CoA. Stage HI, which is called the common catabolic pathway, consists of the citric acid cycle followed by the electron transport chain and oxidative phosphorylation. The main function of catabolism is to produce ATP molecules. 

Now we can calculate the energy yield for the entire catabolic pathway (citric add cycle, electron transport chain, and oxidative phosphorylation combined). According to Section 13.5, every acetyl CoA entering the citric add cycle produces 3 NADH and 1 FADH2 plus 1 GTP, which is equivalent in energy to 1 ATP. Thus, 10 ATP molecules are formed per molecule of acetyl CoA catabolized. 

Mitochondria are cigar-shaped organelles with both an outer and an inner membrane. The inner membrane has many folds and contains the enzymes for the electron transport chain and oxidative phosphorylation. The enzymes for the citric acid cycle are attached to or near to the surface of the inner membrane. 

Crista (cristae) A fold in the inner mitochondrial membrane that project into the mitochondrial matrix. The enzymes of the electron transport chain and oxidative phosphorylation are located mainly on the cristae. 

The egg and the embryonic cell are well endowed with bioenergetic pathways. The multiple-enzyme systems involved in glycolysis, the hexose monophosphate shunt, the Krebs cycle, the electron transport chain, and oxidative phosphorylation have all been found in the vertebrate embryo. In the embryonic and in the mature cell, oxidation through the Krebs cycle, electron transport, and coupling of oxidation and phosphorylation occur in mitochondria. The chemical energy provided by these pathways is needed for normal development because if either glycolysis, Krebs cycle, or electron transport chain inhibitors are administered in vivo or added to explanted chick or sea urchin embryos, embryonic development is arrested. 

---