Which nitrogenous base is only present in RNA?

Uracil is the nitrogenous base that is uniquely found in RNA, distinguishing it from DNA, which contains thymine instead. In RNA, uracil pairs with adenine during the process of transcription, replacing thymine, which is not present in RNA’s structure. The incorporation of uracil is crucial for the stability and functionality of RNA, as it participates in protein synthesis and various regulatory functions within the cell.

Adenine and cytosine are present in both RNA and DNA, which is why they do not fit the criterion of being exclusive to RNA. Thymine is another base that, while found in DNA, is absent from RNA entirely, further solidifying uracil's unique role in the latter's molecular composition. Thus, uracil's presence in RNA is significant and reflects the fundamental biochemical distinctions between RNA and DNA.