Figure 1 represents a segment of DNA. Radiation can damage the nucleotides in a DNA molecule. To repair some types of damage, a
single nucleotide can be removed from a DNA molecule and replaced with an undamaged nucleotide. Which of the four labeled bonds in Figure 1 could be broken to remove and replace the cytosine nucleotide without affecting the biological
information coded in the DNA molecule?
This inquiry is lacking details. However, what is referenced represents a DNA repair process. This approach is termed base excision repair. Overall, glycosylases are crucial in this repair system, detecting and removing damaged bases.
One aspect to consider when choosing which bond to sever involves the codon that will be formed following the base's removal, determining if this resulting codon (a sequence of three bases) will produce an identical protein as the one made with a normal cytosine.
NOTE: In this base excision repair scenario, a glycosylase identifies and eliminates the faulty cytosine. Once it's gone, the leftover nucleotide backbone from the removed cytosine is also excised, and the gap is filled and secured by various enzymes involved in this repair mechanism.
