Question

in E. coli, the process of DNA replication results in only one error in 10^7 nucleotides added. Which enzymatic activity accounts for this high degree of accuracy?a. 3' to 5' exonucleaseb. 5' to 3' exonucleasec. helicased. primasee. RNase H

Answer 1

a. 3' to 5' exonuclease

Step-by-step explanation:

DNA polymerase adds nucleotides to the nascent DNA strand in a 5' to 3' direction. The added nucleotides are complementary to those in the original strand following the rules of base pairing (A pairs with T, C with G).

Sometimes mistakes are made and a wrong nucleotide is incorporated, thus generating a mismatch between the two DNA strands. In those cases, the DNA polymerase has the ability to recognize the mismatch through its proofreading activity in the opposite direction of polymerization (3' to 5'), remove the wrong nucleotide (exonuclease) and incorporate the correct one. This mechanism prevents frequent mutations from happening during DNA replication.