6.21 in textbook

[505766240]

6.21 The two strands of the nucleic acid DNA are held together by hydrogen bonding between four organic bases. The structure of one of these bases, thymine, is shown below. (a) How many protons can this base accept? (b) Draw the structure of each conjugate acid that can be formed. (c) Mark with an asterisk any structure that can show amphiprotic behavior in aqueous solution.

For a), why is the answer 2 (one from each N)? Only nitrogen can accept protons and not the two oxygen atoms? Also, for c), how do you know which compounds show amphiprotic behavior?

[Nicole Ju 3H]

From a post in 2019: "Oxygen is unlikely to share its electrons here because it's much more electronegative than Nitrogen. If oxygen shared its electrons, it would have a + charge on it, which is not very stable. That's why nitrogen is more favored in terms of accepting a hydrogen."

For part c, I'm not completely sure, but I think any of the structures with one proton added to it can act as both an acid or a base (it can donate this proton or accept another proton on the other Nitrogen atom).