Genetic Code

In-depth explanation of Genetic Code

The genetic code is the set of rules by which nucleotide triplets, called codons, specify amino acids in proteins. With four bases read in threes there are 64 possible codons, of which 61 code for the 20 standard amino acids and three act as stop signals, UAA, UAG and UGA. The codon AUG serves as the start signal and also codes for methionine. The code is redundant, or degenerate, because most amino acids have several codons, and it is nearly universal across known life. Codons are read without overlap, so a single nucleotide change can alter one amino acid or none at all.

Going deeper: Genetic Code

Key ideas: Triplet codons: 64 combinations encode 20 amino acids plus 3 stops (UAA, UAG, UGA); AUG is both start and methionine. The code is degenerate (several codons per amino acid, often differing in the third base), unambiguous and nearly universal. Number of codons equals 4 cubed.

Common mistakes and connections: Students think degenerate means ambiguous; it means redundant, one codon never gives two amino acids. A silent mutation changes the codon without changing the amino acid, a missense changes it, nonsense creates a stop, a frameshift (insertion or deletion not multiple of 3) is most disruptive. Links to protein synthesis.

Visualization of Genetic Code

Of the 64 possible triplets, 61 code for the 20 standard amino acids and 3 act as stop signals, so most amino acids have several codons. The interactive lesson shows this as a live animation or chart.

Worked example and use case

The codons GGU, GGC, GGA and GGG all specify the amino acid glycine.

Where Genetic Code fits in Biochemistry, Environment & Industry

Genetic Code is topic 28 of 127 in Biochemistry, Environment & Industry.

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