Multiple choice Which of the following enzymes breaks the phosphodiester bond within a polynucleotide? Exonucleases Topoisomerases Endonucleases Helicases Reveal answer Fill a bubble to check yourself C Correct answer Explanation Endonucleases are enzymes that cleave the phosphodiester bond within a polynucleotide chain, in contrast to exonucleases, which cleave phosphodiester bonds at the end of a polynucleotide chain.