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From amino acids to bases

Each amino acid in the protein needs one codon, and the codon is three bases. In addition one stop codon is needed, and it does not become an amino acid. The coding part of the mRNA must therefore have three bases times the number of amino acids plus one. Introns in eukaryotes have been cut out before this mRNA is translated, so they are not in the count. A protein of fifty amino acids is a short protein, but the arithmetic is the same for long ones. If you forget the stop codon, the mRNA is three bases too short.

3(n+1)3(n + 1)bases in the coding part, with the stop

Symbols

nnnumber of amino acids
33bases per codon
11stop codon

Example

A protein has 50 amino acids.

Bases, with the stop: 3⋅(50+1)=1533 \cdot (50 + 1) = 153.

The start codon is the first amino acid, methionine. It is already inside the fifty, not an extra.
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← The codon · From DNA to mRNA →

Part of Biology 2: From gene to protein.