Template:Approved Article Talk
Approved Article Talk is a very large biological molecule found in almost every cell and is responsible for providing the information necessary for the development and reproduction of all living organisms. Every living organism has its own unique DNA sequence similar to a 'barcode' or 'fingerprint'. DNA acts like a template transfering information from a string of genes within the DNA molecule to a ribosome, a biomachine that can translate the code and assemble a protein molecule from amino acids. While every cell in an organism has identical DNA, each different cell type will synthesize the 10,000 - 20,000 proteins common to most cells along with an additional set of unique proteins that defines the specialized functions of that particular cell type.
Important genetic discoveries in DNA research spanning many decades includes the realization that the seemingly simple DNA molecule, and not the more complex protein molecule, is responsible for the internally coded, inheritible information defining the genotype which provides the necessary instructions to produce the phenotype, or outward physical manifestation an organism.[1] A further significant discovery was that the paired bases were found to exist in equal proportions. this led to the discovery of the duplex structure of DNA, usually referred to as the "double-helix", that enables the complementary replication of DNA in living organisms. The most important feature of the duplex model is the introduction of the concept of complementarity. Complementarity has come to explain the entire sequence of events in the expression of genetic functions. [2]
A single stranded DNA is a long polymer comprised of simple repeating units called nucleotides which form a sugar/phosphate backbone. Attached to each sugar molecule (deoxyribose) is one of four bases; adenine (A), thymine (T), guanine (G) or cytosine (C). In most organisms, DNA is in a double-helix formation consisting of two DNA strands coiled around each other in a head-to-tail "antiparallel" orientation. Each base is structural complementary of its opposing base; adenine always pairs with thymine and guanine always pairs with cytosine. These complementary base pairs are identical in size and shape and will fit between the backbones of double stranded DNA in only one of four configurations TA, AT, GC and CG. The strands are held together by hydrogen bonds between the bases. A sequence of three nucleotides form a codon on the DNA strand that encodes the information for one amino acid residue assembled later into a protein. Most genes have a series of codons that code for a whole protein. This complementarity forms the basis of semi-conservative DNA replication — making it possible for DNA to be copied relatively easily, while accurately preserving its information content.
The entire DNA sequence of genes in any organism is called its genome and in eukaryotes most DNA is stored inside the cell nucleus. Nuclear DNA is subdivided into chromosomes and each contain many genes. In humans there 23 pairs of chromosomes in a typical cell. In bacteria, there is no nuclear membrane around the DNA, which is in a region called the nucleoid. Some organelles in eukaryotic cells (mitochondria and chloroplasts) have their own DNA with a similar organisation to bacterial DNA. Viruses have a single type of nucleic acid, either DNA or RNA, directly encased in a protein coat called the capsid.