Adenosine triphosphate, coupled reactions

Adenosine triphosphate, coupled reactions and. 1128-1129 function of, 157, 1127-1128 reaction with glucose, 1129 structure of, 157, 1044 S-Adenosylmethionine, from methionine, 669 function of, 382-383 stereochemistry of, 315 structure of, 1045 Adipic acid, structure of, 753 ADP, sec Adenosine diphosphate Adrenaline, biosynthesis of, 382-383 molecular model of, 323 slructure of, 24... 

The energy released in catabolic pathways is used in the electron-transport chain to make molecules of adenosine triphosphate, ATP. ATP, the final result of food catabolism, couples to and drives many otherwise unfavorable reactions. 

ADP (adenosine diphosphate) and ATP (adenosine triphosphate) are complex organic molecules (Fig. 17.9) that, in essence, differ only hy the presence of an extra phosphate group in ATP. In the coupled reaction with glucose, about 38 mol of ATP are synthesized for every mole of glucose consumed. This gives an overall free energy change for the coupled reaction of... 

A remarkable feature of the bioenergetic oxidation reactions of nutrients in cells is the fact that they are always coupled to another reaction, that of synthesis of the energy-rich chemical substance adenosine triphosphate (ATP) from adenosine diphosphate (ADP) and phosphate (oxidative phosphorylation Engelgardt and Ljubimova, 1939) ... 

The cell stores chemical energy in the form of energy-rich metabolites. The most important metabolite of this type is adenosine triphosphate (ATP), which drives a large number of energy-dependent reactions via energetic coupling (see p. 16). 

FIGURE 1-25 Adenosine triphosphate (ATP). The removal of the terminal phosphory] group (shaded pink) of ATP, by breakage of a phos-phoanhydride bond, is highly exergonic, and this reaction is coupled to many endergonic reactions in the cell (as in the example in Fig. 1 —26b). 

Liynses. These enzymes catalyze conversions, which are more complex than those of the other groups, and must involve at least two separate stages in the reaction The overall result is the synthesis of a molecule I rnili two components w ith a coupled breakdown of adenosine triphosphate, or some oiher nucleoside triphosphate. In general, this may be written ... 

The oxygen formed clearly comes from H20 and not from C02, because photosynthesis in the presence of water labeled with lgO produces oxygen labeled with 180, whereas carbon dioxide labeled with 180 does not give oxygen labeled with 180. Notice that the oxidation of the water produces two electrons, and that the formation of NADPH from NADP requires two electrons. These reactions occur at different locations within the chloroplasts and in the process of transferring electrons from the water oxidation site to the NADP reduction site, adenosine diphosphate (ADP) is converted to adenosine triphosphate (ATP see Section 15-5F for discussion of the importance of such phosphorylations). Thus electron transport between the two photoprocesses is coupled to phosphorylation. This process is called photophosphorylation (Figure 20-7). 

Fats, carbohydrates, and proteins are metabolized in the body to yield acetyl CoA, which is further degraded in the citric acid cycle to yield two molecules of CO2 plus a large amount of energy. The energy output of the various steps in the citric acid cycle is coupled to the electron-transport chain, a series of enzyme-catalyzed reactions whose ultimate purpose is to synthesize adenosine triphosphate (ATP). 

Firefly luciferase catalyzes the reaction of adenosine triphosphate and a substituted benzothiazole luciferin. The quantum yield of the reaction is high and therefore measurement of the enzyme offers good sensitivity. Coupling of luciferase to other molecules is a problem because there is a highly reactive amino group in the active site that must be protected from reaction with coupling rei ents (36, 37). 

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