How many effective codons are there for the synthesis of twenty amino acids ?

Question

Accepted Answer

The question asks about the number of effective codons involved in the synthesis of twenty amino acids. The correct answer is Option 4, which states that there are 61 effective codons. Let's explore why this is the correct answer and why the other options are incorrect.

1. **Explanation for Option 4 (Correct Answer: 61 effective codons):**
   - In the genetic code, there are 64 possible codons, which are sequences of three nucleotides. These codons are responsible for coding amino acids during protein synthesis.
   - Out of these 64 codons, 3 are stop codons (UAA, UAG, UGA) that do not code for any amino acids but instead signal the termination of protein synthesis.
   - This leaves 61 codons that are responsible for coding the 20 standard amino acids. These 61 codons are referred to as "effective codons" because they directly participate in the synthesis of amino acids.
   - The redundancy in the genetic code, where multiple codons can code for the same amino acid, is known as codon degeneracy. Despite this redundancy, all 61 codons are actively used in the process of translating mRNA into proteins.

2. **Explanation for why the other options are incorrect:**
   - **Option 1 (64 codons):** While there are indeed 64 total codons, not all of them are effective in coding for amino acids. As mentioned, 3 of these are stop codons, which do not contribute to amino acid synthesis. Therefore, the number of effective codons is not 64.
   - **Option 2 (32 codons):** This number is significantly lower than the actual number of effective codons. It does not account for the full range of codons that code for amino acids, and thus, it is incorrect.
   - **Option 3 (41 codons):** Similar to Option 2, this number is also too low. It does not accurately reflect the number of codons that are actively involved in coding for the 20 amino acids.

In conclusion, Option 4 is the correct answer because it accurately represents the number of codons that are effective in the synthesis of amino acids, excluding the stop codons.