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 occur whenever bonds are formed or broken between molecules. Why certain atoms combine with which other atoms is a complex question which is explained exhaustively by quantum chemistry. The simple version is that atoms bond together electromagnetically based on the properties of their electron shells.cientists combine substances to cause chemical reactions. Oxygen combines with iron in a chemical reaction to form iron oxide, which is more commonly known as rust. Chemists may perform chemical reactions.