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.
Reactions require an input of energy to initiate the reaction; this is called the activation energy (E A). Activation energy is the amount of energy required to reach the transition state. The source of the activation energy needed to push reactions forward is typically heat energy from the surroundings.