<P> An IUPAC code that specifically excludes one of the three nucleotides can be complementary to an IUPAC code that excludes the complementary nucleotide . For instance, V (A, C or G - "not T") can be complementary to B (C, G or T - "not A"). </P> <Table> <Tr> <Th> Symbol </Th> <Th> Description </Th> <Th_colspan="5"> Bases represented </Th> </Tr> <Tr> <Td> </Td> <Td> adenine </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> cytosine </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> guanine </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> thymine </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> U </Td> <Td> uracil </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> U </Td> </Tr> <Tr> <Td> </Td> <Td> weak </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> strong </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> amino </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> keto </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> purine </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> Y </Td> <Td> pyrimidine </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> not A (B comes after A) </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> not C (D comes after C) </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> not G (H comes after G) </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> V </Td> <Td> not T (V comes after T and U) </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> N or - </Td> <Td> any base (not a gap) </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> </Table> <Tr> <Th> Symbol </Th> <Th> Description </Th> <Th_colspan="5"> Bases represented </Th> </Tr> <Tr> <Td> </Td> <Td> adenine </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr>

Explain the role of complementary base pairing in the double helix structure of dna