Uence shown above has two mutational differences from the first sequence. Specifically, the third codon is ttg versus ctc in the first sequence. These two codons are two mutational steps away from each other. Supposing that the ctc sequence gave rise to the ttg sequence, do you think it is more likely that the one difference intermediate was ttc or ctg
Answers
It's common to have multiple ATG codons in an mRNA sequence. Generally, the first ATG serves as protein translation starting site and is considered as a start codon if that ATG is at the beginning of a full and functional open reading frame. This is because the specific motifs and structures of the mRNA sequence has to be integrated correctly into a ribosome, a protein translation machinery, to initiate the translation process. In some cases, two ATG codons are closely located in the 5' end of mRNA, one might generate a truncated protein with few amino acid residues only, but another can result in a functional protein. In this case, the second one can be considered as start codon for that functional protein sequence. This phenomenon is considered as a translational regulation of a functional gene