The self-replicating molecule forming the hereditary material as chromosomes in the nuclei of eukaryotes and as strands in prokaryotes. It is a nucleic acid made up of two chains or strands of nucleotides composed of deoxyribose sugar and the bases adenine, cytosine, guanine and thymine (referred to as ‘nucleobases’). The two strands wind round each other and are linked by hydrogen bonds between specific complementary bases to form a spiral ladder-shaped molecule called the double helix. DNA functions in three general ways: 1. replication (or DNA synthesis): during cell division (i.e., mitosis), DNA uncoils, with each strand creating a new partner from the surrounding material. This amounts to ‘unzipping’ the double strand down the middle by means of relatively simple chemical reactions, with the other half of each new single strand being recreated by ‘drowning’ each half in a ‘soup’ of the four nucleases. Errors in replication can give rise to mutations; 2. sexual reproduction: each parent contributes one of the two strands in the DNA of the offspringy; and 3. protein production: DNA governs the production of proteins, as well as other molecules essential to cell functioning. In fact, the sequence of nucleotides along a DNA strand defines a protein, and the relationship between this sequence and the amino acid sequence of the protein is the result of cellular rules of translation. Together, these rules are referred to as the ‘genetic code’. In many organisms, only a small part of the nucleotide sequence seems to encode for protein. The remaining parts of the sequence, called ‘junk DNA’, estimated to constitute about 95% of the human genome, may have a number of (as yet unknown) functions, one of which is to regulate the production of protein during development (and are thus named ‘regulatory sequences’). In now seems evident that DNA includes from genes at least eight retroviruses that become incorporated into human DNA during our evolution. It is thought that these viral genes in DNA have important functions in human reproduction, even though they are alien to our genetic ancestry. DNA was first isolated as a distinct molecule by the Swiss physician and biologist Friedrich Miescher (1844-1895) in 1869.
See Acrosome, Adenine, Allele, Amino acids, Carcinogen, Cell, Central dogma of molecular biology, Chromatid, Chromatin, Chromosome, Competence (embryology), Copying errors, Cytosine, Deoxyribose, DNA double helix, Eukaryote cell (or organism), Gene, Genome, Guanine, MECP2 gene, Methylation, Mitosis, Molecular biology, Mosaicism, Mutation (biology), Mutagens, Myoblast, Nucleic acid, Nucleiod, Nucleotide, Prokaryote cell (or organism), Protein-folding problem, Purines, Pyrimidines, Retrovirus, Ribose, Recombinant DNA (rDNA), Regulatory (or regulator) genes, Structural genes, Thymine, Translation (genetics)