Question

DNA and RNA have four bases. Three of them are common. Which base is not common in DNA and RNA?

• A. Adenine
• B. Guanine
• C. Thymine
• D. Cytosine

Answer 1

The correct option is C Thymine

DNA stands for deoxyribonucleic acid and RNA stands for ribonucleic acid.

They are polynucleotide chains with many pentose sugar molecules, phosphates and nitrogenous bases (purines and pyrimidines).

DNA differs from RNA in the nature of sugar and pyrimidines.

DNA has deoxyribose sugar, while RNA has ribose sugar.

Nitrogenous bases are nitrogen-containing compounds with a ring structure.

Nitrogenous bases can be of two types - Purines and pyrimidines.

Among purines, adenine and guanine, both are present in DNA and RNA.

The pyrimidine bases are cytosine, uracil and thymine.

DNA has thymine and cytosine, while RNA has uracil and cytosine.

Hence, thymine is not present in RNA and uracil is not present in DNA while adenine, guanine and cytosine are common in both DNA and RNA.

The diagram below shows purines and pyrimidines with double and single ring structures respectively.