12. DNA\'s function in cells lies in its double-helical structure with complemen
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12. DNA's function in cells lies in its double-helical structure with complementary bases that form H bonds to each other (See page 1062 in our text). Several of those H bonds in one DNA molecule provide enough stability yet flexibility for the H bonding interaction to temporarily dissociate and thus allow DNA to unravel in order to allow its replication and other functions. The structure of one of those bases, thymine (T) is shown below. Thymine forms 2 H bonds to adenine (A) (again see p. 1062; also see p. 1061 for the structures of all of the bases). Tautomers are molecules that differ in the position of an H atom. The structure of a tautomer of thymine is shown below, 1f this tautomer, rather than the stable form of thymine, were present in a strand of DNA during its replication, what would be the result? Questions to Consider: (1) What base's structure resembles that of the tautomer the most in its number of H-bonding acceptor and donor atoms (i.e. the total number of H bonds it can form with another base)? (2) With what base can the base of your answer in (1) form H bonds?Explanation / Answer
Tautomerization of thymine from keto to an enol form at the C4 leads to the pairing with 'G' that in turn causes the transition to C-G during DNA replication.
Here, N3 is hydrogen donor and C4 and C2 are acceptors. But, mostly C4 involve in the tautomerization rather C2.
As mentioned above enol form of thymine pairs with guanine rather adenine by means of 3 hydrogen bonds (C2, N3 and C4) that in turn leads to the transition of T-A to C-G.
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