Now, when our ribosome reads this mutated mRNA strain, it will use the genetic code. But now, because we have a shift in the reading frame, what will happen is the codons will change. So the first codon in this case is Cua. The first codon in this case is Cu g. But because Cua and Cu g basically code for the same exact amino acid, leucine, the first amino acid is not changed. But look what happens to the next. Because we insert this single nucleotide into our sequence, it shifts all the other nucleotides and that changes the codons that are read by the ribosome.