The life on the Earth is present in a lot of very diverse forms, from the smallest units of life such as prions or viruses up to the largest known living organisms. Since 1869 when the existence of a molecule carrying the information of life – DNA - was discovered, or more precisely, since 1953 when James Watson & Crick have proposed the double helix structure of DNA, the understanding of life has dramatically changed.
Now we know that the diversity of life is determined by a set of nucleic acid molecules encoding genes - the units containing necessary information for the production of proteins or functional RNA molecules (tRNA, rRNA, microRNA…). The basic principle of creation of proteins lies in the transcription (expression) of the genetic information into mRNA and its consequent translation into sequence of amino acids (see the youtube animation).