GENE EXPRESSION
Although the information encoded in DNA is the basis for determining which proteins will be contained in any given cell, that information is not used directly. The sequence of bases in DNA determines the sequence of amino acids in polypeptides through a related nucleic acid, ribonucleic acid (RNA), which serves as an intermediary between DNA and protein. When a protein-coding gene is expressed, an RNA copy is made of the information in the DNA. This RNA copy provides the information that directs protein synthesis.

The first major step of gene expression is transcription, the synthesis of RNA molecules complementary to the DNA. The second key event is translation, in which RNA is used as a coded template to direct protein synthesis. In eukaryotes, transcription takes place in the nucleus and translation occurs in the cytoplasm.