Hydrolysis

Hydrolysis is a chemical process in which a molecule is cleaved into two parts by the addition of a molecule of water. This is distinct from a hydration reaction, in which water molecules are added to a substance, but no covalent bonds are broken.

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Under physiological conditions (i.e. in dilute aqueous solution), a hydrolytic cleavage reaction, where the concentration of a metabolic precursor is low (on the order of 10^-3 to 10^-6 molar), is essentially thermodynamically irreversible. To give an example:

A + H₂O → X + Y

$K_{d}={\frac {\left[X\right]\left[Y\right]}{\left[H_{2}O\right]\left[A\right]}}$

Assuming that x is the final concentration of products, and that C is the initial concentration of A, and W = [H₂O] = 55.5 molar, then x can be calculated with the equation:

${\frac {x\times x}{W\left(C-x\right)}}=K_{d}$

let K_d×W = k

then $x={\frac {-k+{\sqrt {k^{2}+4kC}}}{2}}$

For a value of C = 0.001 molar, and k = 1 molar, x/C > 0.999. Less than 0.1% of the original reactant would be present once the reaction is complete.

This theme of physiological irreversibility of hydrolysis is used consistently in metabolic pathways, since many biological processes are driven by the cleavage of anhydrous pyrophosphate bonds.

See also

• adenosine triphosphate
• biopolymer
• condensation polymer
• oleochemical