RNA primers on each Okazaki fragment are replaced with DNA by which enzyme?

RNA primers on each Okazaki fragment are replaced with DNA by which enzyme?

• A. DNA polymerase III
• B. DNA polymerase I
• C. DNA ligase
• D. Primase

Answer: (B)

RNA primers on Okazaki fragments must be removed and replaced with DNA to join fragments into a continuous strand. In bacteria, DNA polymerase I is the enzyme that does this cleanup and patchwork: it has a 5' to 3' exonuclease activity that removes RNA primers and a 5' to 3' polymerase activity that fills the resulting gaps with DNA. After the primer is replaced, DNA ligase seals the remaining nick to create a continuous sugar-phosphate backbone. The other enzymes don’t perform both primer removal and gap filling (they either synthesize DNA or merely seal nicks).

RNA primers on Okazaki fragments must be removed and replaced with DNA to join fragments into a continuous strand. In bacteria, DNA polymerase I is the enzyme that does this cleanup and patchwork: it has a 5' to 3' exonuclease activity that removes RNA primers and a 5' to 3' polymerase activity that fills the resulting gaps with DNA. After the primer is replaced, DNA ligase seals the remaining nick to create a continuous sugar-phosphate backbone. The other enzymes don’t perform both primer removal and gap filling (they either synthesize DNA or merely seal nicks).