The number of punctuation codons in a genetic code are

Options

A. `2+3=5`
B. `1+3=4`
C. `1+1=2`
D. 3

Answer

To determine the number of punctuation codons in a genetic code, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Codons**:
- Codons are sequences of three nucleotides in mRNA that correspond to specific amino acids or signal the start or end of protein synthesis.

2. **Identify the Total Number of Codons**:
- There are a total of 64 possible codons that can be formed from the four nucleotides (A, U, C, G) in mRNA.

3. **Differentiate Between Coding and Non-Coding Codons**:
- Out of the 64 codons, 61 codons code for amino acids, while 3 codons do not code for any amino acid.

4. **Identify the Punctuation Codons**:
- The punctuation codons include:
- **Start Codon**: AUG, which codes for Methionine and initiates protein synthesis.
- **Stop Codons**: UAA, UGA, and UAG, which signal the termination of protein synthesis.

5. **Count the Punctuation Codons**:
- There is 1 start codon (AUG) and 3 stop codons (UAA, UGA, UAG).
- Therefore, the total number of punctuation codons is 1 (start) + 3 (stop) = 4.

### Final Answer:
The number of punctuation codons in a genetic code is **4**.

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