The specific @A00472@ between two complementary strands of @N04245@ that results from the formation of hydrogen bonds between the base components of the @N04255@ of each strand: A=T and G=C in @D01597@, A=U and G=C (and sometimes G=U) in @R05386@ (the lines indicate the number of hydrogen bonds). Single-stranded nucleic acid molecules can adopt a partially double-stranded structure through intrastrand base pairing.