Which base is found in RNA but not in DNA?

Which base is found in RNA but not in DNA?

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

Answer: (A)

The bases differ between RNA and DNA, and the one that appears in RNA but not in DNA is uracil. RNA uses adenine, cytosine, guanine, and uracil, while DNA uses adenine, cytosine, guanine, and thymine. Uracil is structurally similar to thymine but lacks a methyl group, which suits RNA’s typically shorter, single-stranded, more flexible role. In RNA, adenine pairs with uracil during base pairing, just as adenine pairs with thymine in DNA. The presence of thymine in DNA (instead of uracil) also helps repair systems distinguish true thymine from uracil that can appear if cytosine deaminates, preserving genetic integrity. Adenine, cytosine, and guanine are shared between both acids, so they do not distinguish RNA from DNA.

The bases differ between RNA and DNA, and the one that appears in RNA but not in DNA is uracil. RNA uses adenine, cytosine, guanine, and uracil, while DNA uses adenine, cytosine, guanine, and thymine. Uracil is structurally similar to thymine but lacks a methyl group, which suits RNA’s typically shorter, single-stranded, more flexible role. In RNA, adenine pairs with uracil during base pairing, just as adenine pairs with thymine in DNA. The presence of thymine in DNA (instead of uracil) also helps repair systems distinguish true thymine from uracil that can appear if cytosine deaminates, preserving genetic integrity. Adenine, cytosine, and guanine are shared between both acids, so they do not distinguish RNA from DNA.