Chapter 6, the keto tautomer is strongly favored over the enol tau-tomer, but more so for thymine than for 5-bromouracih
As we discussed for ethjdium in Chapter 6, intercalating agents are flat molecules containing several polycyclic rings that bind to the equally fist purine or pyrimidine bases of DNA, just as the bases bind or stack with each other in the double helix, intercalating agents, such as proflavin, acridine, and ethidium, cause the deletion or addition of a base pair or, even a few base pairs. When such deletions or additions arise in a gene, they can have profound consequences on the translation of its messenger RNA because they shift the coding sequence oul of its proper reading frame, as we shall see when we consider the genetic code in Chapter 15.
How do intercalating agents cause short insertions and deletions? One possibility in the case of insertions is that, by slipping between the bases in the template strand, these mutagens cause the DNA polymerase to insert an extra nucleotide opposite the intercalated molecule. (The intercalation of one of these structures approximately doubles the typical distance between two base pairs.) Conversely, in the case of deletions, the distortion to the template caused by the presence of an intercalated molecule might cause the polymerase to skip a nucleotide.
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