Base pair: Difference between revisions

Revision as of 19:19, 19 August 2005

Revision as of 11:24, 13 September 2005

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* Gbp = giga base pairs = 1,000,000,000 bp

In case of single stranded DNA/RNA we talk about [[Nucleotidenucleotide]]s, abbreviated nt (or knt, Mnt, Gnt), rather than base pairs, as they are not paired.

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The larger nucleic acids, adenine and guanine, are members of a class of doubly-ringed chemical structures called [[purine]]s; the smaller nucleic acids, cytosine and thymine (and uracil), are members of a class of singly-ringed chemical structures called [[pyrimidine]]s. Purines are only complementary with pyrimidines: pyrimidine-pyrimidine pairings are energetically unfavourable because the molecules are too far apart for hydrogen bonding to be established; purine-purine pairings are energetically unfavourable because the molecules are too close, leading to electrostatic repulsion. The only other possible pairings are GT and AC; these pairings are mismatches because the pattern of hydrogen donors and acceptors do not correspond.

As [[hydrogen bond]]s are not very strong, the two nucleotides will separate on temperatures higher than 94 [[degree Celsius|°C]].

Chemical analogs of nucleotides can take the place of proper nucleotides and establish non-canonical base-pairing, leading to errors in [[DNA replication]] and [[Transcription (genetics)|DNA transcription]]. Some analogs are [[carcinogen]]s; others are [[chemotherapy]] drugs.