I've never seen any material from AAMC which required you to know them to answer a question. I also did not bother to memorize them.
With that said, no one can guarantee you with 100% certainty that something will not be on the test. You can be sure though that memorizing them will be very, very low yield.
No, you don't need to memorize them for sure. However, I'd make sure to be able to recognize which one is which, or at the very least, differentiate purine from pyrimidine.