define start codon
Start 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.