Question

DNA polymerase fails to recognize that an incorrect nucleotide has been incorporated, resulting in a mismatch. Which repair pathway will correct this mistake?
A. Base excision repair
B. Mismatch repair
C. Direct repair by methyltransferases
D. Nucleotide excision repair

Answer 1

Answer:

The correct answer is B. Mismatch repair

Explanation:

Mismatch repair pathway recognizes the mismatched base pair that incorporated during DNA replication and then excise that incorrect base. After excision, it repairs the DNA.

The mismatched daughter strand is distinguished from the parent strand by mismatch repair system as the parent strand is methylated at some bases but the daughter strand is not methylated.  

Three proteins help in mismatch repair MutH, MutL, MutS. Mut H and Mut S recognize the mismatch, Mut H excise the unmethylated strand from 5' side. Then helicase and exonuclease enzymes clave the segment from cleavage site to beyond the mismatch base.  

The gap created by this action is filled by DNA polymerase and sealed by enzyme DNA ligase.