DNA Is the Abbreviation for Deoxyribonucleic Acid,

DNA is the abbreviation for deoxyribonucleic acid, which is a complex giant molecule that contains, in chemically coded form, the information needed for a cell to make proteins (DNA Pp). DNA is a "ladderlike double-stranded nucleic acid that forms the basis of genetic inheritance in all organisms, except for a few viruses that have only RNA" (DNA Pp). DNA is organized into chromosomes, and, in organisms other than bacteria, is found only in the cell nucleus (DNA Pp). It is made up of two chains of nucleotide subunits, with each nucleotide containing a purine, (adenine or guanine), or pyrimidine (cytosine or thymine) base (DNA Pp). These bases link up with one another, the adenine links with thymine, and cytosine with guanine, to form base pairs that "connect the two strands of the DNA molecule like the rungs of a twisted ladder" (DNA Pp).

The base sequence is preserved from generation to generation by the specific way in which the pairs form, thus, hereditary information is stored as a specific sequence of bases (DNA Pp). A set of three bases, called a codon, acts as a blueprint for the manufacture of a particular amino acid, the subunit of a protein molecule (DNA Pp). The meaning of each of the codons in the genetic code has been worked out by molecular geneticists, thus, codons are identified by the initial letters of the constituent bases, for example, "the base sequence of codon CAG is cytosine-adenine-guanine" (DNA Pp). There are four different bases, meaning that there must be "4 & #215; 4 & #215; 4 = 64 different codons" (DNA Pp). Generally, proteins are made up of only twenty different amino acids, therefore many amino acids have more than one codon, for example, "GGT, GGC, GGA and GGG all code for the same amino acid, glycine" (DNA Pp).

The information encoded by the codons is transcribed by messenger RNA and is then translated into amino acids in the ribosomes and cytoplasm (DNA Pp). Because the sequence of codons determines the exact order in which amino acids are linked during manufacture, it also determines the kind of protein that is to be produced (DNA Pp). Since proteins are the main structural molecules of living matter and, as enzymes, regulate all aspects of metabolism, it can be "seen that the genetic code is effectively responsible for building and controlling the whole organism" (DNA Pp). It is possible to determine the sequence of bases along the length of DNA by cutting the molecule into small portions, using restriction enzymes, "this technique can also be sued for transferring specific sequences of DNA from one organism to another" (DNA Pp).

The oldest sequenced DNA to be found belongs to a nemonychid weevil that was trapped in amber from the Cretaceous period and estimated to be 120-135 million years old (DNA Pp). In 1994, American researchers extracted DNA from human hair that was 10,000 years old and that same year, dinosaur DNA was extracted from unfossilized dinosaur bones found in a coal mine in Utah (DAN Pp).

In 1991 hikers in the Italian Alps found a frozen body of a man who was later identified by scientists, using DNA analysis, to be approximately 5, 000 years old (Poinar Pp). Through the years, scientists have learned that the normally fragile DNA molecule can exist for hundreds, thousands and even millions of years in "certain extraordinary preserved specimens" (Poinar Pp). The sophisticated tools of molecular biology, used most often to foretell an organism's genetic future, can also be used to decipher an organism's past (Poinar Pp). Today, scientists are "exploiting the techniques of gene amplification and sequencing to decipher biological events that took place in the very distant past' (Poinar Pp). Reading the ancient history encoded in DNA from people, animals and plants, allows researchers to "fill in missing links on phylogenetic trees or to identify the remains of organisms long extinct" (Poinar Pp).

The study of DNA damage and repair was initiated and has continued to be conducted for many years by scientists interested in the effects of radiation on biological systems (Sancar Pp). As a result, these topics have been only of peripheral interest to the majority of biological scientists interested in replication, transcription, gene regulation, and cell cycle (Sancar Pp). In fact, DNA damage and repair occur under physiological conditions as part of normal cellular events, therefore, "even a reductionist description of cellular processes must necessarily encompass DNA repair" (Sancar Pp). In recent years, an important conceptual breakthrough in molecular biology has been the realization of the intimate interconnections between basic cellular reactions, cell cycle, replication, transcription, recombination, repair, previously believed to function more or less independently (Sancar Pp). Such an integrative approach is expected to lead to a better understanding of the cell and the organism, which in turn would help in "designing better approaches to cancer treatment and may even help with our long-standing quest for slowing the aging process" (Sancar Pp).