Reaction, endergonic exergonic

AGr Gibbs free-cnergy change The energy difference between reactants and products. When AG° is negative, the reaction is exergonic, has a favorable equilibrium constant, and can occur spontaneously. When AGC is positive, the reaction is endergonic, has an unfavorable equilibrium constant, and cannot occur spontaneously. 

For ATP to carry out this function, it has to be produced from adenosine diphosphate (ADP) in an endergonic reaction that must be driven by another exergonic metabolic reaction. One exergonic reaction step that occurs in the overall oxidation of glucose in the cell is the oxidation of 3-phosphoglyceraldehyde to 3-phosphoglycerate by pyruvate, for which AG = —29,300 Jmol ... 

AG, is directly associated with the direction in which a particular chemical reaction can proceed. If AG < 0 for a given set of conditions of a particular reaction, then the reaction will proceed spontaneously in the indicated direction until equilibrium is reached. Conversely, if AG is positive, then energy will be needed to shift the reaction further from its equilibrium condition. See Helmholtz Energy Endergonic Exergonic Enthalpy Entropy Thermodynamics Biochemical Thermodynamics... 

If suitable systems of ligands could be found such that light reaction is endergonic and dark reaction is exergonic, then the net result will be decomposition of water. 

When AG of a reaction is negative, the reaction is exergonic and tends to go toward completion when AG is positive, the reaction is endergonic and tends to go in the reverse direction. When two reactions can be summed to yield a third reaction, the AG for this overall reaction is the sum of the AGs of the two separate reactions. This provides a way to couple reactions. 

The overall consumption of one molecule of acetyl-CoA in the citric acid cycle is an exergonic process AG° = —60 kJ mol-1. All but two of the individual reactions are exergonic. Step 2 (citrate— isocitrate) and step 8 (malate —>oxaloacetate) are endergonic (Fig. 12-3). 

The energetics of the endergonic part of the pathway, the reduction of CO2 to methylene-H4MPT, has been studied by analyzing the reverse reaction, the exergonic conversion of formaldehyde to CO2 and Hz. ... 

H2-scavenging methanogen because the reaction is endergonic at the H2 concentrations encountered. However, the reaction is exergonic if the H2 partial pressure is maintained at <10 atm by the methanogen with a net co-culture. 

If the forward reaction is exergonic and the reverse reaction is endergonic, increased temperature will shift the system toward more reactants, decreasing the ratio of products to reactants and decreasing the equilibrium constant. 

Carboxylation of RuBP to form the six-carbon intermediate is significantly endergonic, whereas the overall reaction is exergonic by about 6 kcal/mol. Overall, the reaction is driven by cleavage of the six-carbon intermediate. Clearly the enzyme controls the conformation of the six-carbon intermediate in a way that favors cleavage and disfavors decarboxylation. The enzyme from R. rubrum is less successful at this than the more complex higher plant enzyme. Metal com-plexation is probably a key to control, and the small subunit might also be involved. 

This reaction is endergonic (AG = +12 kcal/mol) under standard conditions but, because ATP levels are very high within mitochondria, and creatine phosphate levels are relatively low, the reaction is exergonic as written and proceeds to the right. Thus, the cellular concentration of metabolites has a drastic effect on the free energy for a reaction, enabling ATP to create phosphorylated compounds with higher phosphoryl transfer potential than itself under standard conditions. 

Knowing whether a given reaction is exergonic or endergonic will not tell you how fast the reaction occurs, because the AG° of a reaction tells you only the difference between the stability of the reactants and the stability of the products it does not tell you... 

The reaction is exergonic under intracellular conditions because the cell drives the reaction by providing a large amount of fructose-1,6-bisphosphate, and by removing the products dihydroxyacetone-P and glyceraldehyde-3-P. (By contrast, under standard conditions—when all products and reactants are present in equal concentrations—the reaction is endergonic because AG° is large and positive, and AG = AG° under standard conditions.)... 

What does the symbol AG° represent How does the sign for AG° indicate whether a reaction is exergonic or endergonic ... 

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