In tRNA, CCA sequence is found at 3 end and G at 5' end. This CCA group is

Options

A. present from the beginning of tRNA formation
B. added after transcription
C. added after translation
D. added before transcription

Answer

To answer the question regarding the CCA sequence found at the 3' end of tRNA and the G at the 5' end, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding tRNA Structure**:
- tRNA (transfer RNA) has a specific structure that includes a 5' end and a 3' end. The 3' end is where the amino acid is attached, and the 5' end typically starts with a guanine (G).

2. **Identifying the CCA Sequence**:
- The CCA sequence at the 3' end of tRNA is crucial because it is the site where the amino acid attaches. This sequence is not present in the primary transcript of tRNA when it is first synthesized.

3. **Formation of tRNA**:
- tRNA is synthesized from DNA through the process of transcription, which produces a precursor tRNA molecule. This precursor undergoes several modifications to become mature tRNA.

4. **Modification of tRNA**:
- During the maturation process of tRNA, the CCA sequence is added to the 3' end. This addition occurs after the transcription of the tRNA gene, meaning that the CCA sequence is not part of the original tRNA transcript.

5. **Final Conclusion**:
- Therefore, the CCA group is added after the transcription of the tRNA, which means the correct answer to the question is that the CCA sequence is added after transcription.