Question

Which one of the following DNA repair systems requires DNA glycosylases?

• A. Base-excision
• B. Direct
• C. Mismatch
• D. Nucleotide-excision

Hint:

In base-excision repair, DNA glycosylases play a crucial role in recognizing and excising damaged bases. This is the first step in repairing single-base lesions.

Answer 1

The Correct Option is A

Base-excision repair (BER) is a DNA repair mechanism that specifically addresses single-base lesions in the DNA. This system requires the activity of DNA glycosylases, which recognize and remove damaged bases by cleaving the glycosidic bond between the base and the sugar-phosphate backbone. After the base is removed, the repair is completed by other enzymes that fill in the gap and ligate the strand. Hence, statement (A) is correct.
- (B): Direct repair does not involve glycosylases. It is a repair process that directly reverses certain types of DNA damage, such as the repair of O6-methylguanine through the action of O6-methylguanine-DNA methyltransferase. Thus, statement (B) is incorrect.
- (C): Mismatch repair corrects errors that occur during DNA replication, such as base-pair mismatches and small insertions or deletions, but it does not require glycosylases. Therefore, statement (C) is incorrect.
- (D): Nucleotide-excision repair (NER) is a process that removes bulky DNA lesions, but it does not involve glycosylases. Instead, it involves the excision of a short single-stranded DNA segment containing the damage. Hence, statement (D) is incorrect.
Thus, the correct answer is (A).