Which of the following is the smallest RNA ?

Options

A. mRNA
B. tRNA
C. Chromosomal RNA
D. Ribosomal RNA

Answer

To determine which of the following is the smallest RNA, we need to analyze the four options provided: mRNA, tRNA, chromosomal RNA, and ribosomal RNA (rRNA).

### Step-by-Step Solution:

1. **Identify the Types of RNA**:
- The options given are:
- mRNA (messenger RNA)
- tRNA (transfer RNA)
- Chromosomal RNA
- rRNA (ribosomal RNA)

2. **Understand the Length of Each RNA Type**:
- **mRNA**: Typically, mRNA can vary in length but is usually several hundred to thousands of base pairs long. For example, a long mRNA can be around 1000 base pairs.
- **tRNA**: Transfer RNA is relatively short, usually consisting of about 75 to 95 nucleotides. In terms of base pairs, it is about 7 to 9 base pairs long.
- **Chromosomal RNA**: This is much larger, with estimates around 3.2 billion base pairs long, as it corresponds to the entire genomic DNA.
- **rRNA**: Ribosomal RNA is also relatively large, as it forms the structural and functional core of ribosomes, but the exact length can vary depending on the type of rRNA.

3. **Compare the Lengths**:
- From the above information, we can summarize:
- mRNA: Hundreds to thousands of base pairs
- tRNA: 7 to 9 base pairs
- Chromosomal RNA: 3.2 billion base pairs
- rRNA: Varies, but generally larger than tRNA

4. **Determine the Smallest RNA**:
- Based on the lengths analyzed, tRNA is the smallest RNA type among the options provided, with only 7 to 9 base pairs in length.

5. **Conclusion**:
- Therefore, the smallest RNA is **tRNA** (transfer RNA).

### Final Answer:
The smallest RNA is **tRNA** (transfer RNA).