The base pairs of a DNA strand are connected by hydrogen bonds. In essence, the genetic code is contained by a unique arrangement of hydrogen bonds. It is believed that upon the replication of a DNA strand there is a probability for proton tunneling to occur which changes the hydrogen bond configuration; this leads to a slight alteration of the hereditary code which is the basis of mutations. Likewise, proton tunneling is also believed to be responsible for the occurrence of the dysfunction of cells (tumors and cancer) and ageing.