At the heart of this book is the riddle of the DNA molecule—both its structure and its implications. DNA stands for deoxyribonucleic acid. It is a molecule found in all organisms, and it contains the genetic code that determines the development, functioning and reproduction of cells. In simple terms, DNA is the molecular blueprint of life.

DNA exists in long chains of molecules known as genes (sections of DNA that contain a complete set of instructions for a protein). These genes are packed into pairs of chromosomes, found within the nucleus of every cell. The specific sequence of molecules found within strands of DNA works as a codewhich builds proteins and determines the features and functions of cells. From this starting point, all organisms are created.

It was speculated before Watson and Crick’s discovery that DNA had a role to play in cell replication, though no one knew how it worked or could prove it.

Thanks to Watson’s and Cricks discovery, we understand much more precisely how DNA works and its role in cell replication.

A simple law determines the way DNA bonds. A and G are purine bases, T and C are pyrimidine. The law is that a purine base can only bond with a pyrimidine base and vice-versa.