Organic Reaction in Metabolisms

Organic Reaction Mechanisms It can be categorized all common biological reactions into four groups - 

Look at ATP. In the figure the bolded region is the recognition part of the molecule, while the polyphosphate is the chemically active portion. Each of the phosphoric acid anhydride bonds is unstable. That is hydrolyzing either will release a lot of energy. 

So why ATP First, we want a compound with intermediate hydrolysis energy so it can pick up energy from some reactions and deliver to others. Second we want a kinetically stable molecule which is thermodynamically unstable. Thus acetic acid anhydride would not work it is thermodynamically unstable to hydrolysis, but it is also kinetically unstable, with the carbonyl carbons wide open to water attack. Phosphoric acid anhydride is equally unstable, but is is sterically protected from water attack - in order to react quickly we need a catalyst -perfect. 

EA is the energy of a system at the start of a process and EB at the end of the process. Q is the heat absorbed by the system and W is the work done by the system. 

Since free energy depends on conditions, chemists tabulate free energies under Standard Conditions, (AG ) 298 K, 1 atm., with all concentrations at 1 M. 

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