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.
Heat: In order to start a fire, the fuel and oxygen reacting with each other must exceed a threshold called the flash point. The flash point is the temperature at which the chemical reaction can combust, producing a flame. Different chemicals have different flash points, some relatively high, and some incredibly low.