Question

In the genetic dictionary, there are 64 codons as

(a) 64 amino acids are to be coded

(b) 64 types of tRNAs are present

(c) there are 44 nonsense codons and 20 sense codons

(d) genetic code is triplet.

Answer 1

Option d is correct. Genetic code is triplet. It means a genetic codon consist of three nucleotides. For example AUG, AUU etc. There are four nucleotides are present in genome: Adenine (A), GUanine (G), Thymine (T) and cytosine (C). These four nucleotides form 64 (4X4X4) codons. These 64 codons code for only 20 amino acids. Infact only 61 out for 64 codes for 20 amino acids and rest three(UAG, UGA and UAA) are stop codons which are also known as terminating codon or nonsense codons. As we know 20 amino acids require only 20 codons and 41 codons are extra. Therefore it is clear that more than one codon codes for same amino acid.