Question: what is the main structural difference between uracil and thymine?
Answer: Thymine is the pyrimidine base of the DNA, whereas Uracil is the pyrimidine base of the RNA. The occurrence of thymine and uracil is a crucial difference as thymine is only found in DNA and uracil is only found in RNA. Methyl group is absent in uracil whereas present in thymine at the C-5 position.