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In the genetic code dictionary, how many codons are used to code for all the 20 essential amino acids : -
A
20
B
64
C
61
D
60
Detailed Solution
Four bases taken three at a time give $4^3 = 64$ codons.
Three of these, UAA, UAG and UGA, are stop (nonsense) codons that do not code for any amino acid.
The remaining $64 - 3 = 61$ codons (sense codons) code for the 20 amino acids. Since there are more codons than amino acids, most amino acids have more than one codon (degeneracy).
AUG codes for methionine and also acts as the start codon.
So 61 codons code for all 20 amino acids.
Three of these, UAA, UAG and UGA, are stop (nonsense) codons that do not code for any amino acid.
The remaining $64 - 3 = 61$ codons (sense codons) code for the 20 amino acids. Since there are more codons than amino acids, most amino acids have more than one codon (degeneracy).
AUG codes for methionine and also acts as the start codon.
So 61 codons code for all 20 amino acids.