Final answer:
The primary difference between the three DNA repair mechanisms—mismatch repair, base excision repair, and nucleotide excision repair—is how the mutation is identified, with each addressing different types of DNA damage and using different processes and enzymes for recognition and repair.
Step-by-step explanation:
The primary difference between mismatch repair, base excision repair, and nucleotide excision repair is: B. how the mutation is identified.
Mismatch repair corrects errors made during DNA replication that are not caught by the polymerase's proofreading activity. Mismatch repair enzymes recognize the incorrectly paired base in the new DNA and remove it, inserting the correct base. Base excision repair targets damaged bases that have occurred due to various chemical reactions, such as oxidation or deamination. Specific enzymes called DNA glycosylases recognize and excise the wrong base, after which DNA polymerase and ligase fill and seal the gap respectively.
In the case of nucleotide excision repair, it is employed for more bulky types of damage, such as pyrimidine dimers caused by UV light exposure. This method involves the removal of a sequence of nucleotides which includes the damage, not just the affected bases, and requires a series of enzymes to recognize the abnormal helix structure caused by the damage, remove the damaged strand, and use DNA polymerase and ligase to fill and seal the gap.