Drawing conjugate acids

[NaomiAbramowicz1H]

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."
How do I go about solving this? I don't understand why the protons are accepted at the Ns and not the Os. Also, how do you draw a conjugate acid? Thanks for any insight!

[Jose Angelo Grajeda 2D]

For part (a), the base can accept two protons (H+), one on each NH-group corner, because nitrogen has a lone pair of electrons available to be donated (and H+ accepted in its place), making those two corners have 2 N-H bonds (instead of just one), and there would be a positive formal charge of +1 on the nitrogen. I think the reason why oxygen (even though it has LPs) doesn't share its electrons is because it's double bonded to the carbon, and also oxygen is more electronegative than nitrogen, so nitrogen is more favorable in sharing its electrons instead of oxygen. If oxygen shared its LP of electrons and accepted a proton in its place, it would have a formal charge of +1, which is not very stable (b/c it's more electronegative than nitrogen). A lot of the times, we see nitrogens donating LPs of electrons in a weak base, and oxygens that are single-bonded to donate electrons as a base, but not this double-bonded oxygen (b/c FC would be +1, not as stable).

The conjugate acid structure is just the original base, with the extra proton (H+) bonded to the nitrogen (where its LP used to be). A conjugate acid is like its original base partner, but would try to lose its H+ to return back to basic form. Since there are two places where this proton can be added, there are two structures to be drawn. And lastly, an amphiprotic solution just means it can either accept H+ (act like a base) or donate H+ (act like an acid), and thymine can do this at those two NH spots. Hope this helps!