21 The Structure of guanine base is shown below 8oxoguanine

#21. The Structure of guanine base is shown below; 8-oxo-guanine is an oxidation modification of DNA that can occur. Does this modification affect Watson-crick base pairing?

Yes, the oxidation occurs on a site that participates in Watson-crickbase pairing

No, the oxidation occurs on a site that does NOT participate in Watson-crickbase pairing.

Solution

The oxidation of guanine to 8-oxoguanine (O8G) in DNA is a frequent transformation that occurs in cells as a result of the metabolic generation of reactive oxygen species or exposure to agents that induce oxidative stress.It has been demonstrated that this modification is both cytotoxic and mutagenic.

Modification at the 8-position does not directly affect the ability of adenine and guanine to form Watson-Crick base pairs,but the presence of the bulky oxygen atom increases their tendency to adopt the syn conformation,thereby providing possibilities for base mispairing.The presence of an O8G base in genomic DNA can lead to a G to T tranversion mutation via an O8G-A base pair with a syn:anti configuration stabilized by two interbase hydrogen bonds.In addition to having reasonable thermodynamic stability,the O8G-A pair is pseudosymmetric about the N-glydosidic bonds which join the bases to the sugars,and is therefore structurally similar to a Watson-Crick base pair.The similarity is particularly striking in the minor groove,where the 8-oxygen atom of O8G lies in the position that would be occupied by the 2-oxygen atom of the thymine base in an A-T base pair.Thus,the O8G-A base pair is not readily recognized by proofreading enzymes.