base pairing The specific association between two complementary strands of nucleic acids that results from the formation of hydrogen bonds between the base com­ponents (adenine [A], guanine [G], thymine [T], cytosine [C], uracil [U] of the nucleotides of each strand (the lines indicate the number of hydrogen bonds):

A=T and G

C in DNA, A=U and G
C (and in some cases GU) in RNA

single-stranded nucleic acid molecules can adopt a partially double-stranded structure through intrastrand base pairing.

base-pair substitution

base-pair substitution There are two main types of mutations within a gene: base-pair substitutions and base-pair insertions or deletions. A base-pair substitu­tion is a point mutation; it is the replacement of one nucleotide and its partner from the complementary deoxyribonucleic acid (DNA) strand with another pair of nucleotides. Bases are one of five compounds—ade­nine, guanine, cytosine, thymine, and uracil—that form the genetic code in DNA and ribonucleic acid (RNA).