Organic molecules that catalyze reactions quickly at relatively low body temperatures are called:

Enzymes.

Enzymes are responsible to make reactions hard to take place, or even very unlikely to happen, to actually happen. They are proteins that have normally an active binding site where molecules may connect to and preform the reaction. The necessary energy to make a reaction occur is less when aided by enzymes and that's what makes of them catalysts so that reactions may occur even when in lower temperatures.