Which of the following RNA has abnormal purine bases:
**Core Concept**
The question tests the understanding of **RNA structure and function**, specifically focusing on the types of RNA and their characteristic base compositions. **Transfer RNA (tRNA)** is known for its unique features, including modified bases.
**Why the Correct Answer is Right**
The correct answer is related to **tRNA**, which contains abnormal purine bases such as **dihydrouridine**, **pseudouridine**, and **thiolated uridines**, in addition to **queuosine** and **wyosine**. These modifications play crucial roles in the proper functioning of tRNA, including **codon recognition** and **stabilization of secondary structure**.
**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because **mRNA (messenger RNA)** primarily contains the standard **adenine**, **guanine**, **cytosine**, and **uracil** bases without the unusual purine bases found in tRNA.
**Option B:** This option is wrong as **rRNA (ribosomal RNA)**, a component of **ribosomes**, also does not typically contain the abnormal purine bases characteristic of tRNA.
**Option D:** This choice is incorrect because **snRNA (small nuclear RNA)**, involved in **splicing** and other **RNA processing** events, does not characteristically have the same abnormal purine bases as tRNA.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that **tRNA**'s unique bases are essential for its function, particularly in ensuring accurate **protein synthesis**. Recognizing the distinct features of different RNA types is crucial for understanding **molecular biology** and **genetics**.
**Correct Answer:** D. tRNA.