Question 23

Uracil is the nucleotide only found in RNA.

Uracil is a nitrogenous base that is unique to RNA, replacing thymine which is found in DNA. This distinction is essential for understanding the structural differences between RNA and DNA.

A) Adenine

Adenine is a purine nucleotide present in both RNA and DNA. It plays a critical role in the structure of nucleotides in both types of nucleic acids, thus it is not exclusive to RNA.

B) Uracil

Uracil is the correct answer as it is specifically found in RNA molecules. It serves as one of the four primary nucleobases in RNA, pairing with adenine during the processes of transcription and translation.

C) Guanine

Guanine is another purine nucleotide that is found in both RNA and DNA. Like adenine, it is not unique to RNA and is integral to the structure of both types of nucleic acids.

D) Thymine

Thymine is a pyrimidine nucleotide that is only found in DNA. It is replaced by uracil in RNA, making it a distinguishing feature of DNA rather than RNA.

Conclusion

Uracil is definitively the nucleotide that is only found in RNA, distinguishing it from DNA which contains thymine. All other options, adenine, guanine, and thymine, are either present in both RNA and DNA or exclusive to DNA, reinforcing that uracil is unique to RNA.