Definitions for start codon
The codon at which translation of mRNA into protein starts, encoding the first amino acid.
Origin: start (indicating first, initial) + codon
The Central dogma of molecular biology describes the process of translation of a gene to a protein. Specific sequences of DNA act as a template to synthesize mRNA. The start codon is the first codon of a messenger RNA transcript translated by a ribosome. The start codon always codes for methionine in eukaryotes and a modified Met in prokaryotes. The most common start codon is AUG. The start codon is almost always preceded by an untranslated region 5' UTR. In prokaryotes this includes the ribosome binding site. Alternate start codons are very rare in eukaryotic genomes. Mitochondrial genomes and prokaryotes use alternate start codons more significantly. For example E. coli uses 83% ATG, 14% GTG, 3% TTG and one or two others. Bioinformatics programs usually allow for alternate start codons when searching for protein coding genes. Note that these alternate start codons are still translated as Met when they are at the start of a protein. This is because a separate transfer RNA is used for initiation.A
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