Base excision repair (BER) differs from nucleotide excision repair (NER) in which of the following ways?

1) NER involves the removal and replacement of DNA containing altered bases, while BER does not. 2) BER involves the removal and replacement of DNA containing altered bases, while NER does not. 3) BER recognizes helix distortions, while NER recognizes specific base damage. 4) BER involves a DNA synthesis step, while NER does not. 5) NER recognizes helix distortions, while BER recognizes specific base damage.

The correct answer is: 5) NER recognizes helix distortions, while BER recognizes specific base damage.

DNA damage that occurs as a result of radiation, oxidizing reagents, chemicals and other mutagens can be repaired. Excision repair repairs single strand DNA damage and it includes:

• Nucleotide excision repair (NER) - it detects and repairs types of damage that distort the DNA double helix such as those of UV radiation (thymine dimers); not only the damaged nucleotide (s) are removed but also a surrounding patch of DNA

• Base excision repair (BER) - it detects and removes certain types of damaged bases (small, non-helix-distorting bases); enzyme glycosylase is responsible for this type of repair