A condensation reaction is responsible for building large molecules.  An enzyme catalyzes the reaction between alcohol groups on adjacent monomer units (eg. glucose).  This results in the production of a polymer and a molecule of water.

A hydrolysis reaction is responsible for breaking down large molecules (eg. digestion).  An enzyme weakens the bond between two parts of a polymer, allowing for the insertion of a water molecule into the bond.  This results in the production of monomers.