What characterizes a chemical reaction?

A chemical reaction is characterized by the breaking and forming of chemical bonds, which results in the transformation of reactants into products. During this process, the existing bonds between atoms in the reactants are broken, and new bonds are formed to create the products. This fundamental aspect of chemistry is essential for understanding how substances interact, combine, or decompose.

While the other options mention biological processes that are critical in the context of life, they do not encapsulate the primary hallmark of a chemical reaction. The transfer of energy between cells can occur during many biological processes, but it doesn't specifically define a chemical reaction. The synthesis of new proteins refers to the process of transcription and translation in protein synthesis, and the replication of DNA involves the copying of genetic material. Though these are vital biological processes, they revolve around specific functions rather than the general definition of a chemical reaction itself.