On translation , mRNA produce a polypeptide chain , which contains 50 amino acids. if `26^( th)` codon of mRNA UUU mutated and changed to UUC , then the polypeptide chain will be

Options

A. Completely changed
B. Partially changed
C. Not changed
D. only one amino acid changed

Answer

To solve the problem, we need to analyze the mutation in the mRNA codon and its effect on the resulting polypeptide chain.

### Step-by-Step Solution:

1. **Identify the Original Codon**: The original 26th codon of the mRNA is UUU.

2. **Identify the Mutated Codon**: The mutated codon is UUC.

3. **Determine the Amino Acids Encoded by Each Codon**:
- The codon UUU codes for the amino acid **Phenylalanine (Phe)**.
- The codon UUC also codes for the amino acid **Phenylalanine (Phe)**.

4. **Analyze the Impact of the Mutation**:
- Since both UUU and UUC code for the same amino acid (Phenylalanine), the mutation does not change the amino acid at the 26th position of the polypeptide chain.

5. **Conclusion**: The overall polypeptide chain remains unchanged because the mutation does not affect the amino acid sequence. Therefore, the polypeptide chain will still contain 50 amino acids, and the amino acid at the 26th position will still be Phenylalanine.

### Final Answer:
The polypeptide chain will remain **not changed**.