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.
Chemical reactions also occur in one of two circumstances: a) the reaction is following a fundamental law of nature (enthalpy-its the nature of things to want to use the smallest amount of energy possible, so when a reaction can occur that produces more energy, it will.