In RNA adenine always pairs with?
Uracil in Watson-Crick base-pairing though non-standard pairs exist.
What scientist determined that adenine always pairs with thymine and cytosine always pairs with guanine?
Those are Chargraff's Rules. You're wrong to think that adenine and thymine are the only pairs however because in RNA, adenine always pairs with uracil. Thymine is not in RNA. Adenine and Guanine are purines. Cytosine, thymine, and uracil are purimidines. Sources: My Science class and textbook Hope this helped!
DNA has a deoxyribose sugar; RNA has ribose sugar. DNA is double stranded; RNA is single. DNA has adenine that pairs with thymine, guanine that pairs with cytosine; RNA has adenine that pairs with uracil, guanine that pairs with cytosine. DNA resides in the nucleus; RNA resides in both the nucleus and the cytoplasm (near ribosomes)