Which structural feature is true of thymine?

Which structural feature is true of thymine?

• A. It is missing a methyl group.
• B. It contains a methyl group.
• C. It lacks nitrogen atoms in the ring.
• D. It is a purine.

Answer: (B)

Thymine has a methyl group attached to the ring. This base is a pyrimidine in DNA, and its structure is 5-methyluracil, meaning a CH3 group sits at the 5-position. This methyl substituent distinguishes thymine from uracil (the RNA base, which lacks the methyl group) and helps DNA-specific processes recognize and maintain the genetic material. Thymine also contains nitrogen atoms in its ring and is not a purine (purines have a larger two-ring structure). So the true structural feature is that thymine contains a methyl group.

Thymine has a methyl group attached to the ring. This base is a pyrimidine in DNA, and its structure is 5-methyluracil, meaning a CH3 group sits at the 5-position. This methyl substituent distinguishes thymine from uracil (the RNA base, which lacks the methyl group) and helps DNA-specific processes recognize and maintain the genetic material. Thymine also contains nitrogen atoms in its ring and is not a purine (purines have a larger two-ring structure). So the true structural feature is that thymine contains a methyl group.