The origin of replication (also called the replication origin) is a particular sequence in a genome at which replication is initiated.
It is the interaction of two or more substances, resulting in chemical changes in them. Chemical reactions take place when some kind of energy is supplied to them. The supplied energy may be in the form of heat, light or mechanical shaking for proper contact between the reactant molecules or electricity.
The energy needed to make a reaction happen is called the activation energy. As everything moves around, energy is needed. The energy that a reaction needs is usually in the form of heat. When a catalyst is added, something special happens. Maybe a molecule shifts its structure.