A Level Biology Practice Exam

Which base is found in RNA but not in DNA?

1. Adenine

2. Thymine

3. Uracil

4. Cytosine

The correct answer is: Uracil

Uracil is indeed the base that is found in RNA but not in DNA. In RNA, uracil (U) pairs with adenine (A) during the formation of RNA strands, replacing thymine (T), which is present in DNA. This distinction is crucial because it highlights the differences in nucleic acid structure and function. RNA is typically single-stranded and serves various functions in the cell, such as coding, decoding, regulation, and expression of genes, while DNA, being double-stranded, primarily serves as the long-term storage of genetic information. The presence of uracil in RNA instead of thymine is also a key factor in the overall stability and structure of nucleic acids, as thymine has a methyl group that contributes to the stability of DNA.