Amino acids which are specified by single codons are

Options

A. phenylalanine and arginine
B. trytophan and methionine
C. valine and proline
D. methionine and arginine

Answer

To solve the question regarding which amino acids are specified by single codons, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Codons and Amino Acids**:
- There are 64 possible codons (triplet combinations of nucleotides) and only 20 amino acids. This means that most amino acids are specified by more than one codon.

2. **Identify Amino Acids Specified by Single Codons**:
- The amino acids that are specified by a single codon are rare. We need to identify them from the options given.

3. **Examine Each Option**:
- **Option 1**: Phenylalanine (UUU, UUC) and Arginine (CGU, CGC, CGA, CGG, AGA, AGG) - Both are specified by multiple codons.
- **Option 2**: Tryptophan (UGG) and Methionine (AUG) - Both are specified by a single codon.
- **Option 3**: Valine (GUU, GUC, GUA, GUG) and Proline (CCU, CCC, CCA, CCG) - Both are specified by multiple codons.
- **Option 4**: Methionine (AUG) and Arginine (CGU, CGC, CGA, CGG, AGA, AGG) - Methionine is specified by a single codon, but Arginine is not.

4. **Conclusion**:
- The only amino acids specified by single codons are Tryptophan (UGG) and Methionine (AUG). Therefore, the correct answer is **Option 2: Tryptophan and Methionine**.

### Final Answer:
The amino acids which are specified by single codons are Tryptophan and Methionine.

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