During the mismatch repair of DNA, the repair enzyme will remove several nucleotides on both DNA...

During the mismatch repair of DNA, the repair enzyme

will remove several nucleotides on both DNA strands.
will remove several nucleotides on one DNA strand.
will remove only the mismatched nucleotide.
will remove the mismatched nucleotide, and the same enzyme will replace it with the correct nucleotide.
is unable to detect mutations.

Expert Solution

Ans: Correct option: Will remove several nucleotides on one strand.

Explanation: During the DNA replication some time proofreading fails and the wrong base is inserted in the growing DNA strand (example adenine with cytosine) then this is called a mismatch. This mistake is corrected by the mismatch repair enzymes. Following are some basic steps of the mismatch repair:

At first, the MutS protein recognizes the mismatch site and binds to it.
MutL protein binds with the MutS and thus forms the MutS-MutL complex.
Now the MutH protein binds with the DNA strand at GATC site.
Due to the looping of the DNA, the MutS-MutL complex comes close to the MutH protein.
After this MutH protein creates a break in the unmethylated strand by its endonuclease activity.
Now several nucleotides flanking the mismatch are removed.
DNA polymerase enzyme fills the gap by adding nucleotides according to the template.
The nick is sealed by the enzyme DNA ligase.

Please see the image below for Steps 1-4.

The explanation for incorrect options:

The nucleotides are removed from only one strand. As template strand is methylated at the GATC site. But immediately after synthesis, the newly synthesized strand is not methylated. In this way, MutH enzyme differentiates the template strand from the new strand and makes a cut in the only in the new strand for the removal of nucleotides.
Several nucleotides (not only mismatched) near the mismatch site are removed by the exonuclease enzyme.
The correct nucleotides are replaced by the DNA polymerase enzyme.
Mismatch repair enzymes detect the mutation and correct it. If the mismatch is not repaired it may lead to cancer.

gladiator answered 2 hours ago

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