Which of the following is correct regarding genetic code ?

Options

A. UUU is the initiation codon which also codes for phenylalanine
B. There are 64 triplet codons and only 20 amino acids
C. Three random nitrogen bases specify the placement of one amino acid
D. UAA is the nonsense codon which also codes for methionine

Answer

To determine which statement regarding the genetic code is correct, let's analyze each option provided in the question systematically.

### Step-by-Step Solution:

1. **Statement Analysis**:
- **Statement 1**: "UUU is the initiation codon which also codes for phenylalanine."
- **Analysis**: UUU does indeed code for phenylalanine, but it is not an initiation codon. The initiation codon is AUG, which codes for methionine. Therefore, this statement is **incorrect**.

2. **Statement 2**: "There are 64 triplet codons and only 20 amino acids."
- **Analysis**: This statement is correct. The genetic code consists of 64 codons (triplets of nucleotides), but there are only 20 standard amino acids. This means that multiple codons can code for the same amino acid, a phenomenon known as redundancy in the genetic code. Therefore, this statement is **correct**.

3. **Statement 3**: "Three random nitrogenous bases specify the placement of one amino acid."
- **Analysis**: This statement is misleading. While it is true that three nitrogenous bases (a codon) specify one amino acid, the term "random" is incorrect. The codons are arranged in a specific order that determines the sequence of amino acids in a protein. Therefore, this statement is **incorrect**.

4. **Statement 4**: "UAA is the nonsense codon which also codes for methionine."
- **Analysis**: UAA is indeed a nonsense codon (also known as a stop codon), but it does not code for any amino acid, including methionine. Methionine is coded by AUG. Therefore, this statement is **incorrect**.

### Conclusion:
Based on the analysis above, the only correct statement regarding the genetic code is **Statement 2**: "There are 64 triplet codons and only 20 amino acids."