Abstract
The genetic information for the development of an organism is stored and inherited by deoxyribonucleic acid (DNA). In higher organisms the DNA is located within the cell nucleus. DNA has the structure of a double helix and contains a specific sequence of four types of nucleotides that are specified by the bases adenine, guanine, cytosine and thymine. Replication of the DNA double helix by DNA polymerase results in the formation of two double helices with identical nucleotide sequences. Expression of the information contained in the DNA requires the synthesis of ribonucleic acid (RNA) copies and subsequent transport of the RNA from the nucleus to the cytoplasm. One type of RNA, called messenger RNA (mRNA), contains the instruction for the amino acid sequence of polypeptides. The translation of the nucleotide sequence of mRNA into the amino acid sequence of polypeptides is facilitated by ribosomes. For the synthesis of each of the different kinds of polypeptides a specific mRNA is expressed. The expression of the genetic information is mainly regulated by direct interactions of control elements located on DNA and RNA with certain protein factors.