Base analogs

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Base analogs are molecules which have a very similar structure to one of the four nitrogenous bases which are used in DNA (adenine, guanine, cytosine or thymine). They form a structure similar to one of the DNA nucleotides and then can be used to form the new strand in semi conservative replication. This means that the base analog is now incorporated into the DNA double helix. Once in the DNA helix, some base analogs change shape. This means if used as a template strand during replication, they will pair with a different base and cause a base change mutation.

An example of a base analog which can be mutagenic is 5-bromouracil which has a similar structure to Thymine so will form hydrogen bonds with Adenine in the template strand. It can then change shape so it is complementary to guanine. This means the base change would be thymine-adenine to guanine-cytosine[1].


  1. Ruvolo, D.H., Maryellen, 2012. Genetics: analysis of genes and genomes, Sudbury, Mass: Jones & Bartlett Learning, p542
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