This thematic block consists of five units on the structure and properties of nucleic acids, the flow of genetic information, and recombinant DNA techniques. The block generally raises the significance of the three main processes in the flow of genetic information replication, transcription and translation. We present a detailed description of the double helix model of Watson and Crick and the forces that stabilize the secondary structure, after addressing the general characteristics of the DNA replication process, with special emphasis on semiconservative and bidirectional character. then it isexplained the transcription of DNA or RNA-dependent synthesis of DNA and protein biosynthesis. The description of the genetic code provides the basic idea of the last process flow of genetic information: the translation or conversion of information encoded in the nucleotide sequence in a functional protein sequence. Finally, it introduces the student to recent advances in the manipulation of nucleic acids.