Nucleic acids base-pairing rules

Nucleic acid hybridization is based on the fact that complementary DNA or RNA sequences will hydrogen bond to one another according to the base pairing rules. 

The Watson-Crick pairing rules for DNA are the consequence not only of the properties of the nucleic acid bases, but of the sugar backgone structure as well... 

As confirmed by the Watson—Crick base pairing rule, the base composition of a nucleic acid follows Chargaff s rule for double-stranded DNAs, the total number of pyrimidine bases is equal to that of purine bases. In terms of mole fraction (x), Xa = Xt, Xg = Cc, and consequently Xq+c = 1 - ( Ca+t)-... 

For a given gene, the corresponding mRNA is complementary to (matches the base pairing of) the strand of the DNA where the information in the gene is stored. The conventions on nucleic acid nomenclature, nucleic acid structure, and the Wat-son-Crick rules for complementary base-pairing are given in Chapter 3. 

Complementary base sequence. For a given sequence of nucleic acids, the nucleic acids that are related to them by the rules of base pairing. 

The nucleotide sequence of a nucleic acid immediately provides plausible models for the approximate secondary structures. The base-pairing patterns, A-T(U) and G-C, are easy to identify and several simple rules can guide selection of folding patterns ... 

According to the Chargaff rule, each nucleic acid has as much adenine as thymine (Table 29-4). There are also equal amounts of guanine and cytosine or 5-methyl cytosine. Because of this, the term base pairing of A/T, G/C, G/5MC, and A/ U is used. The rule applies well to DNA, but there are often significant deviations in the case of RNA. This difference is closely related to the differences in physical structure between DNA and RNA (see also Section 29.4). 

The formation of messenger RNA should also conform to the rule of base pairing. In any case, it can be demonstrated that template RNA is complementary to DNA since one can make hybrid nucleic acids, which are double-stranded molecules consisting of one DNA and one RNA chain (cf. Section 3). 

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