Which one of the following is correct?

Options

A. Introns are present in mRNA and exons are present in rRNA
B. Codons are present in mRNA and anticodons in tRNA
C. Every intron is a set of three terminator codons.
D. Exons are present in eukaryotes while introns are present in prokaryotes.

Answer

To determine which statement is correct, we will analyze each of the provided options one by one.

### Step-by-Step Solution:

1. **Understanding Introns and Exons**:
- **Introns** are non-coding sequences found in the primary RNA transcript that are removed during RNA processing.
- **Exons** are coding sequences that remain in the mature mRNA after introns are spliced out.

2. **Analyzing Option A**:
- The statement claims that "introns are present in mRNA and exons are present in rRNA."
- This is incorrect because introns are indeed present in the primary mRNA transcript, but exons are not found in rRNA; they are found in mRNA.

3. **Analyzing Option B**:
- The statement claims that "codons are present in mRNA and anticodons are present in tRNA."
- This is correct because codons, which are sequences of three nucleotides, are found in mRNA and are read by tRNA, which has complementary sequences called anticodons.

4. **Analyzing Option C**:
- The statement claims that "every intron is a set of three terminator codons."
- This is incorrect. Terminator codons (UAG, UAA, UGA) are not introns; they are specific codons that signal the termination of translation and are found in exons.

5. **Analyzing Option D**:
- The statement claims that "exons are present in eukaryotes while introns are present in prokaryotes."
- This is also incorrect. Both exons and introns are primarily found in eukaryotic genes. Prokaryotes typically do not have introns.

6. **Conclusion**:
- After analyzing all options, we find that the only correct statement is Option B: "Codons are present in mRNA and anticodons are present in tRNA."

### Final Answer:
The correct option is **B: Codons are present in mRNA and anticodons are present in tRNA.**

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