In a mRNA molecule, untranslated regions (UTRs) are present at

Options

A. 5'-end (before start codon)
B. 3'-end (after stop codon)
C. Both (a) and (b)
D. 3'-end only

Answer

**Step-by-Step Solution:**

1. **Understanding mRNA Structure**:
- mRNA (messenger RNA) is a single-stranded molecule that carries genetic information from DNA to the ribosome, where proteins are synthesized.

2. **Identifying UTRs**:
- Untranslated Regions (UTRs) are segments of the mRNA that do not code for proteins. They play important roles in the regulation of translation and stability of the mRNA.

3. **Locating UTRs on mRNA**:
- UTRs are found at both ends of the mRNA molecule:
- The **5' UTR** is located upstream of the start codon (AUG), which is the first codon that is translated into an amino acid.
- The **3' UTR** is located downstream of the stop codon (UAA, UAG, UGA), which signals the end of translation.

4. **Conclusion**:
- Since UTRs are present before the start codon and after the stop codon, they are located at both the 5' and 3' ends of the mRNA molecule.

5. **Final Answer**:
- Therefore, the untranslated regions (UTRs) are present at both the 5' end and the 3' end of the mRNA molecule. The correct option is **C**: both at the 5' and 3' ends.

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