Where is the start codon located? where is the start codon located? in the dna just upstream of where transcription starts at the upstream end of the 3' untranslated region (utr) at the downstream end of the 5' untranslated region (utr) at the very start (5' end) of the mrna?

The answer is 'at the very start (5' end) of the mrna. According to the central dogma, dna -> rna -> protein. messenger rna carries genetic code from dna to be translated into protein by the ribosome. One difference between Rna and dna is that rna has uracil while dna has thiamine bases. Therefore the start codon on mrna will be AUG rather ATG.