In the genetic code dictionary, how many codons are used to code for all the 20 essential amino acids ?

Options

A. 61
B. 60
C. 20
D. 64

Explanation

To solve the question regarding how many codons are used to code for all 20 essential amino acids, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Codons**: Codons are sequences of three nucleotides in mRNA that correspond to specific amino acids. Each codon is made up of combinations of four nucleotides: adenine (A), cytosine (C), guanine (G), and uracil (U) in RNA.

2. **Calculating Total Codons**: Since codons are triplets, we can calculate the total number of possible codons using the formula \(4^3\) (because there are 4 bases and each codon consists of 3 bases).
\[ 4^3 = 64 \]
Therefore, there are a total of 64 different codons.

3. **Identifying Stop Codons**: Out of these 64 codons, 3 are designated as stop codons (UAA, UGA, UAG). These codons signal the termination of protein synthesis.

4. **Calculating Codons for Amino Acids**: To find the number of codons that code for amino acids, we subtract the stop codons from the total codons:
\[ 64 - 3 = 61 \]
Thus, there are 61 codons that code for amino acids.

5. **Amino Acids Representation**: These 61 codons are used to code for the 20 essential amino acids. This means that multiple codons can correspond to a single amino acid, a phenomenon known as codon redundancy or degeneracy.

### Final Answer:
In summary, the number of codons used to code for all 20 essential amino acids is **61**.

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