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| [[Image:DNA-Animation.gif|thumb|220px|Three-dimensional model of the structure of part of a DNA double helix.]]
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| '''Talk Checklist''' 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 [[gene]]s within the DNA molecule to a [[ribosome]], a biomachine that can [[translation|translate]] the code and assemble a [[protein]] molecule from [[amino acid]]s. While every [[Cell (biology)|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.
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| 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.<ref>Kornberg, Arthur. "DNA Replication". W.H.Freeman and Co. (1980) p13</ref> 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. <ref>Insert footnote text here</ref>
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| 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.
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| The entire DNA sequence of genes in any organism is called its [[genome]] and in [[eukaryote]]s most DNA is stored inside the [[cell nucleus]]. Nuclear DNA is subdivided into [[chromosome]]s 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 ([[mitochondrion|mitochondria]] and [[chloroplast]]s) have their own DNA with a similar organisation to bacterial DNA. [[Virus]]es have a single type of [[nucleic acid]], either DNA or RNA, directly encased in a protein coat called the [[capsid]].
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