الفهرس 
Historical review of DNA research
Cardiovascular disordersOnly 14 pages are availabe for public view
 |  | from | 137 |  |  |
| | | from | 137 | | |
Abstract
DNA is a nucleic acid that contains the genetic information used in the development and functioning of all known living organisms. DNA is present not only in chromosomes in the nucleus, but also in mitochondria. The main role of DNA molecules is the long-term storage of genetic information. DNA is a long polymer made from repeating units called nucleotides. In living organisms, DNA does not usually exist as a single molecule, but instead as a tightly-associated pair of molecule. These two long strands turn around each other in the shape of a double helix. The nucleotide repeats contain both the segment of the backbone of the molecule, which holds the chain together, and a base, which interacts with the other DNA strand in the helix. The backbone of the DNA strand is made from alternating phosphate and sugar residues. DNA contains the information needed to construct other components of cells, such as proteins and RNA molecules. The information carried by DNA is held in the sequence of pieces of DNA called genes. Transmission of genetic information in genes is achieved via complementary base pairing. For example, in transcription, when a cell uses the information in a gene, the DNA sequence is copied into a complementary RNA sequence through the attraction between the DNA and the correct RNA nucleotides. Usually, this RNA copy is then used to make a matching protein sequence in a process called translation which depends on the same interaction between RNA nucleotides. Alternatively, a cell may simply copy its genetic information in a process called DNA replication.