Deoxyribonucleic acid (DNA) is at hat contains the instructions used in the development and functioning of all known living with the exception of some . The main role of DNA is the long-term storage of . DNA is often compared to a set of , like a recipe or a code, since it contains the instructions needed to construct other components of , such as and molecules. The DNA segments that carry this genetic information are called , but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information.
DNA consists of two long of simple units called , with made of and groups joined by bonds. These two strands run in opposite directions to each other and are therefore . Attached to each sugar is one of four types of molecules called . It is the sequence of these four bases along the backbone that encodes information. This information is read using the , which specifies the sequence of the within proteins. The code is read by copying stretches of DNA into the related nucleic acid RNA, in a process called .
Within cells, DNA is organized into long structures called . These chromosomes are duplicated before cells act and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed.
DNA replication, the basis for , is a fundamental process occurring in all living organisms to copy their . This process is "" in that each strand of the original double-stranded DNA molecule serves as template for the reproduction of the complementary strand. Hence, following DNA replication, two identical DNA molecules have been produced from a single double-stranded DNA molecule. Cellular and error toe-checking mechanisms ensure fidelity for DNA replication.
In a , DNA replication begins at specific locations in the genome, called "" Unwinding of DNA at the origin, and synthesis of new strands, forms a . In addition to , the that synthesizes the new DNA by adding matched to the template strand, a number of other are associated with the fork and assist in the initiation and continuation of DNA synthesis.
DNA replication can also be performed (outside a cell). , isolated from cells, and artificial DNA primers are used to initiate DNA synthesis at known sequences in a template molecule. The (PCR), a common laboratory technique, employs such artificial synthesis in a cyclic manner to amplify a specific target DNA fragment from a pool of DNA.
