A common type of chemical damage to DNA is produced by a spontaneous reaction termed deamination, in which a nucleotide base loses an amino group (NH₂). The amino group is replaced with a keto group (C=O) by the general reaction shown in Figure Q6−13. Write the structures of the bases A, G, C, T, and U and predict the products that will be produced by deamination. By looking at the products of this reaction—and remembering that, in the cell, these will need to be recognized and repaired can you propose an explanation for why DNA does not contain uracil?

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N NH₂ H₂O NH, H N