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'''Deoxyribonucleic acid''' (DNA) is an [[organic compound|organic]] [[chemical compound]] made up of [[molecule]]s shaped like a [[double helix]], or like a continually-twisted ladder. The individual monomeric building blocks of DNA (and other nucleic acids) are [[nucleotide]]s, which themselves consist of three principle moieties: A nitrogenous base, a [[sugar]], and a [[phosphate]] group.   

'''Deoxyribonucleic acid''' (DNA) is an [[organic compound|organic]] [[chemical compound]] made up of [[molecule]]s shaped like a [[double helix]] (like a twisted ladder). The individual building blocks of DNA (and other nucleic acids) are [[nucleotide]]s, which themselves consist of three principle parts: A nitrogenous base, a [[sugar]], and a [[phosphate]] group.   

DNA contains [[gene]]s that code for [[protein]]s by first being transcribed into [[RNA]]. All organisms contain DNA, except for a few [[virus]]es. Offspring of sexually producing organisms contain DNA from both parents.

DNA contains [[gene]]s that help create [[protein]]s by first being transcribed into [[RNA]]. All plants and animals contain DNA, except for a few [[virus]]es. Offspring of sexually reproducing organisms contain DNA from both parents.

==History==

==History==

==Modern understanding==

==Modern understanding==

[[Image:818.gif|right|thumb|Structure of DNA.]]

[[Image:818.gif|right|thumb|Structure of DNA.]]

Small lengths of DNA called [[gene]]s serve as the instructions for the body to carry out its functions and give rise to the physical traits of the organism. <ref>"Eye-color genes, through the proteins they encode, direct the amount and placement of melanin in the iris." [http://www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file=answers%2Fgenetics%2Fans_044.html Ask A Scientist - Genes and eye color]</ref> DNA is packaged into [[chromosomes]]. Each individual human being has 23 pairs of chromosomes, where one set is inherited from his/her mother and the other set is inherited from his/her father. 22 of these chromosomes are referred to as autosomes, while the remaining chromosome is the sex chromosome that determines gender.

Small lengths of DNA called [[gene]]s serve as the instructions for the body to carry out its functions and give rise to the physical traits of the organism. <ref>"Eye-color genes, through the proteins they encode, direct the amount and placement of melanin in the iris." [http://www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file=answers%2Fgenetics%2Fans_044.html Ask A Scientist - Genes and eye color]</ref> DNA is packaged into [[chromosomes]]. Each individual human being has 23 pairs of [[chromosome]]s, where one set is inherited from his/her mother and the other set is inherited from his/her father. 22 of these chromosomes are referred to as [[autosome]]s, while the remaining chromosome is the sex chromosome that determines gender.

[[Prokaryotic DNA]] is circular (a closed loop), while [[eukaryotic DNA]] is linear (with ends) with the exception of [[Mitochondrial DNA]] and chloroplast DNA which is separate from that of the eukaryotic organism. Both mitochondria and chloroplasts were thought to once be prokayotic organisms that became symbiotes within eukaryotic organisms, this explains why they still retain their circular DNA.  The ends of eukaryotic DNA is protected by [[telomere]]s, which are joined together in knots, except when the cell is undergoing [[mitosis]]. DNA in [[prokaryote]]s usually consists only of one closed loop chromosome.<ref>Campbell, Neil A, et. al. ''Biology''. 6th ed. San Francisco: Benjamin Cummings, 2002. 299, 530-31.</ref>

[[Prokaryotic DNA]] is circular (a closed loop), while [[eukaryotic DNA]] is linear (with ends) with the exception of [[Mitochondrial DNA]] and chloroplast DNA which is separate from that of the eukaryotic organism. Both mitochondria and chloroplasts were thought to once be prokayotic organisms that became symbiotes within eukaryotic organisms, this explains why they still retain their circular DNA.  The ends of eukaryotic DNA is protected by [[telomere]]s, which are joined together in knots, except when the cell is undergoing [[mitosis]]. DNA in [[prokaryote]]s usually consists only of one closed loop chromosome.<ref>Campbell, Neil A, et. al. ''Biology''. 6th ed. San Francisco: Benjamin Cummings, 2002. 299, 530-31.</ref>

Some viral [[genome]]s are composed of DNA, such as that of the [[influenza]] virus.

Some viral [[genome]]s are composed of DNA, such as that of the [[influenza]] virus.

Mutations in DNA accumulate over time and build up to create differences between organisms. Most mutations in DNA are harmless and don't affect the phenotype of the organism. Others can have beneficial effects, but some can disrupt important functions. Many diseases such as Autism and Ellis-van Creveld syndrome have been shown to occur due to these harmful genetic mutations.

[[Mutation]]s in DNA accumulate over time and build up to create differences between organisms. Most mutations in DNA are harmless and don't affect the external appearance of the organism. Others can have beneficial effects, but some can disrupt important functions. Many diseases such as Autism and Ellis-van Crevice syndrome have been shown to occur due to these harmful genetic mutations.

DNA is [[transcription|transcribed]] into [[mRNA]], which is in turn [[translation|translated]] into [[proteins]] built from [[amino acids]]. Additionally, DNA maybe transcribed into functional RNAs such as ribosomal (rRNA) or transfer (tRNA) that do not undergo translation. [[RNA]] can also be reverse-transcribed back into DNA, which is the called [[Complementary DNA]] or [[cDNA]].

DNA is [[transcription|transcribed]] into [[mRNA]], which is in turn [[translation|translated]] into [[proteins]] built from [[amino acids]]. Additionally, DNA maybe transcribed into functional RNAs such as ribosomal (rRNA) or transfer (tRNA) that do not undergo translation. [[RNA]] can also be reverse-transcribed back into DNA, which is the called [[Complementary DNA]] or [[cDNA]].