Thymine is a nitrogenous base that is found in DNA molecules but not in RNA molecules, according to Vision Learning. Instead of thymine, RNA molecules utilize uracil.
DNA and RNA are both comprised of nucleotides that bind to a sugar backbone. The DNA nucleotide bases include adenine, cytosine, guanine and thymine. The RNA nucleotide bases include adenine, uracil, guanine and cytostine. Another difference between the two compounds is their structure. DNA molecules are double-stranded and their nucleotides are bound together by hydrogen bonds. DNA molecules also utilize deoxyribose as their sugar backbone. RNA molecules are single-stranded and utilize ribose as their sugar backbone, according to Vision Learning.