two other species the genetic code appears to be universal. In addition to coding for
amino acids particular triplet sequences also indicate the beginning (Start) and the
end (Stop) of a particular gene. Only one start codon exists (ATG) which also codes for
the amino acid methionine, whereas three dedicated stop codons are available (TAT,
TAG and TGA) (Fig. 5.9). A sequence flanked by a start and a stop codon containing
a number of codons that may be read in-frame to represent a continuous protein
sequence is termed anopen reading frame(ORF).5.4 Location and packaging of nucleic acids
5.4.1 Cellular compartments
In general, DNA in eukaryotic cells is confined to the nucleus and organelles such as
mitochondria or chloroplasts which contain their own genome. The predominant RNA
species are however normally located within the cytoplasm. The genetic information
of cells and most viruses is stored in the form of DNA. This information is used toFig. 5.9The genetic code. Note that the codons in blue represent the start codon (ATG) and the three
stop codons.149 5.4 Location and packaging of nucleic acids