Transcription is the process by which the genetic information in DNA is copied to produce several types of RNA molecules. The enzyme for RNA synthesis is RNA polymerase and this enzyme unites the individual nucleotides into the RNA product. Transcription occurs in three stages, initiation, elongation, and termination. Eukaryotic genes contain introns, which are sequences that do not code for an amino acids, and are removed from the transcript by a process of splicing. The final mRNA molecule contains only the protein coding sequences or exons.
Genes are also divided into structural and regulatory types.
Structural genes encode proteins, whereas regulatory ones carry out various regulatory functions. The Genetic Code. The clear answer is that at least any three letters of the bases provides enough combinations to code for the twenty amino acids, i.e. with three letters, a triplet code, some 64 different possibilities occur. Note that including several codons for start and stop, each amino acid is encoded by more than one triplet. This condition is called degenerate, since each amino acid has several codons rather than just one.