Adenosine diphosphate biochemical reactions

Phosphate condensation reactions play an essential role in metabolism. Recall from Section 14.6 that the conversion of adenosine diphosphate (ADP) to adenosine triphosphate (ATP) requires an input of free energy ADP -I-H3 PO4 ATP +H2O AG° — +30.6kJ As also described in that section, ATP serves as a major biochemical energy source, releasing energy in the reverse, hydrolysis, reaction. The ease of interchanging O—H and O—P bonds probably accounts for the fact that nature chose a phosphate condensation/hydrolysis reaction for energy storage and transport. 

As an example of a set of chemical reactions in aqueous solution that are of biochemical interest, consider the hydrolysis of adenosine triphosphate to adenosine diphosphate and inorganic phosphate in the neighborhood of pH 7. The... 

ATP plays a central role in cellular maintenance both as a chemical for biosynthesis of macromolecules and as the major soirrce of energy for all cellular metabolism. ATP is utilized in numerous biochemical reactions including the eitric acid cycle, fatty acid oxidation, gluconeogenesis, glycolysis, and pyruvate dehydrogenase. ATP also drives ion transporters sueh as Ca -ATPase in the endoplasmic reticulum and plasma membranes, H+-ATPase in the lysosomal membrane, and Na+/K+-ATPase in the plasma membrane. Chemieal energy (30.5 kJ/mol) is released by the hydrolysis of ATP to adenosine diphosphate (ADP). 

Chapters 3-5 have described the calculation of various transformed thermodynamic properties of biochemical reactants and reactions from standard thermodynamic properties of species, but they have not discussed how these species properties were determined. Of course, some species properties came directly out of the National Bureau of Standard Tables (1) and CODATA Tables (2). One way to calculate standard thermodynamic properties of species not in the tables of chemical thermodynamic properties is to express the apparent equilibrium constant K in terms of the equilibrium constant K of a reference chemical reaction, that is a reference reaction written in terms of species, and binding polynomials of reactants, as described in Chapter 2. In order to do this the piiTs of the reactants in the pH range of interest must be known, and if metal ions are bound, the dissociation constants of the metal ion complexes must also be known. For the hydrolysis of adenosine triphosphate to adenosine diphosphate, the apparent equilibrium constant is given by... 

More complicated structures that form with longer chains or rings also exist. The biochemically most important polyphosphate is adenosine triphosphate, ATP, which contains three phosphorus tetrahedral units linked by -O-P-0- bonds. The hydrolysis of ATP to adenosine diphosphate, ADP, by the rupture of an 0-P bond releases energy that is used by cells to drive biochemical reactions within the cell. ATP + H2O ADP + HP04 " A//= - 41 kJ... 

This is the first reaction in the biochemical pathway called glycolysis. A phosphoryl group is transferred from a donor molecule, adenosine triphosphate, to the recipient molecule, glucose. The products are glucose-6-phosphate and adenosine diphosphate. This enz)rme, called hexokinase, is an example of a transferase. 

The triphosphate end of ATP is the part of the molecule that is important in the transfer of biochemical energy. The key reaction in this energy delivery system is the transfer of a phosphoryl group, —A from ATP to another molecule. For example, during the hydrolysis of ATP in water, a phosphoryl group is transferred from ATP to water. The products of this hydrolysis are adenosine diphosphate (ADP) and a phosphate ion, often referred to as an inorganic phosphate, P or simply as phosphate. 

Ion-binding studies with biological molecules can be important in elucidating fundamental biochemical reaction systems in relation to bioenergetics, enzyme activation and membrane transport [182]. For example, the adenosine triphosphate (ATP)—adenosine diphosphate (ADP) cycle is one of the processes of primary importance to cellular energy systems and association constants determined [427—430] for metal—ATP and metal—ADP complexes are therefore of considerable interest Table 2.5). The constants may be obtained from measure-... 

ATP is the principal carrier of biochemical energy. It is considered an energy-rich compound because the hydrolysis of ATP to yield adenosine diphosphate (ADP) and inorganic phosphate is spontaneous under aqueous biochemical conditions. (a) Write a balanced equation for the reaction of ATP with water to yield ADP and inorganic phosphate ion. [Hint Hydrolysis reactions are just the reverse of condensation reactions (Section 22.8).] (b) What would you expect for the sign of the free-ener-gy change for this reaction (c) ADP can undergo further hydrolysis. What would you expect for the product of that reaction ... 

Figure 7.5 Adenosine diphosphate (ADP)-ribosylation biochemical reactions. Mono-ADP-ribosyltransferases (ARTs) and poly-ADP-ribose pol5mierases Poly (PARPs) catalyse the ADP-ribose moiety of NAD transfer to amino acid residues. ADP-ribosyl cyclases generate cyclic ADP-ribose and 2-phospho-cyclic ADP-ribose from NAD and NADP, respectively. Both molecules trigger cyclic ADP-ribose cytosolic Ca " elevation, presumably by activating the ryanodine receptor in the endoplasmic/sarcoplasmic reticulum (RER). SIRTl catalyses a reaction that couples protein deacetylation to NAD hydrolysis.

A key spontaneous biochemical reaction is the hydrolysis of a high-energy molecule called adenosine triphosphate (ATP) to adenosine diphosphate (ADP) ... 

An important feature of biochemical reactions of metabolism and respiration is the coupling of pairs of reactions, which can result in the driving of a nonspontaneous reaction by the progress of a spontaneous reaction. The hydrolysis of adenosine triphosphate (abbreviated by ATP) to form adenosine diphosphate (abbreviated by ADP) and phosphoric acid (abbreviated by P) is shown in Figure 7.3. This is a spontaneous reaction that drives a number of usehil reactions in various organisms. 

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