NCERT · Class 12 · Biology · Molecular Basis of InheritanceDescribe the salient features of the Genetic Code. Explain why the genetic code is said to be degenerate, universal, and unambiguous.

Introduction to Genetic Code\nThe genetic code is the set of rules by which information encoded in genetic material (DNA or mRNA sequences) is translated into proteins by living cells. It specifies the correspondence between nucleotide triplets (codons) and amino acids.

Salient Features of the Genetic Code

• Triplet Nature: Three adjacent nucleotides constitute a codon. There are $4^3 = 64$ possible codons, out of which 61 codons code for amino acids and 3 codons act as stop/termination codons.
• Degeneracy (Redundancy): Most amino acids are specified by more than one codon (except Tryptophan and Methionine). For example, Valine is coded by GUU, GUC, GUA, and GUG. This protects against harmful mutations.
• Universality: The genetic code is nearly universal across all living organisms, from bacteria to humans. For instance, the codon UUU codes for Phenylalanine in both E. coli and human beings. This strongly supports common ancestry.
• Unambiguous (Specific): One codon specifies only one particular amino acid, never more than one. This ensures precision in protein synthesis.
• Comma-less / Non-overlapping: The code is read continuously in a series of three nucleotide groups without any punctuation or overlapping between adjacent codons.
• Start and Stop Codons: AUG acts as the initiator codon (codes for Methionine and acts as a start signal). UAA, UAG, and UGA are stop codons that do not code for any amino acid and terminate polypeptide chain synthesis.

Conclusion\nThe precision, redundancy, and universality of the genetic code make it an exceptionally efficient system for translating genetic messages into functional structural and enzymatic proteins.