1.3 NA is a double helix Antiparallel strands of the double helix are organized in opposite orientation, so that the 5 end of one strand is aligned with the 3 end of the other strand Base pairing describes the specific(complementary Interactions of adenine with thymine or of cytosine with thymine in a DNA double helix(the former is replaced by adenine with uracil in double helical RNA) Complementary base pairs are defined by the pairing reactions In double helical nucleic acids(A with T in DNA or with U in RNA and C with G Supercoiling describes the coiling of a closed duplex DNA in space so that It crosses over its own axis 消当Antiparallel strands of the double helix are organized in opposite orientation, so that the 5′ end of one strand is aligned with the 3′ end of the other strand. Base pairing describes the specific (complementary) interactions of adenine with thymine or of cytosine with thymine in a DNA double helix (the former is replaced by adenine with uracil in double helical RNA). Complementary base pairs are defined by the pairing reactions in double helical nucleic acids (A with T in DNA or with U in RNA, and C with G). Supercoiling describes the coiling of a closed duplex DNA in space so that it crosses over its own axis. 1.3 DNA is a double helix