Out of 64 codons, how many of them code for stop signal?

Options

A. 3
B. 2
C. 5
D. 4

Answer

To solve the question, we need to identify how many of the 64 codons function as stop signals in the genetic code.

### Step-by-Step Solution:

1. **Understanding Codons**: Codons are sequences of three nucleotides in mRNA that correspond to specific amino acids or signal the termination of protein synthesis. In total, there are 64 possible codons (4 nucleotides: A, U, C, G, raised to the power of 3).

2. **Identifying Stop Codons**: Among the 64 codons, there are specific codons that do not code for any amino acids but instead signal the end of protein synthesis. These are known as stop codons.

3. **Listing Stop Codons**: The three stop codons are:
- UAG (Amber)
- UAA (Ochre)
- UGA (Opal)

4. **Counting Stop Codons**: From the list, we can see that there are a total of 3 stop codons.

5. **Conclusion**: Therefore, out of the 64 codons, **3 codons code for stop signals**.

### Final Answer:
**3**

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