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 least amount of energy needed for a chemical reaction to occur. For example, striking a match on the side of a matchbox provides the activation energy, in the form of heat, necessary for the chemicals in the match to catch fire.