Complex sentence: When a codon is artificially substituted for a synonymous codon it often results in a lethal change and cell death, believed to be due to ribosomal stalling and early termination of protein synthesis.
Split into simpler sentences: When a codon is artificially substituted for a synonymous codon it often results in a lethal change and cell death. This is believed to be due to ribosomal stalling and early termination of protein synthesis.