What is a characteristic difference between BER and NER regarding the type of damage they address?

Base Excision Repair (BER) and Nucleotide Excision Repair (NER) are two distinct DNA repair mechanisms that target different types of DNA damage.

The characteristic difference highlighted in the correct response relates to the types of damage that each repair system addresses. NER is specifically designed to recognize and repair bulky DNA lesions, such as those caused by ultraviolet (UV) radiation, which can create issues like thymine dimers. These lesions can disrupt the DNA double helix and hinder replication if left unrepaired. NER involves excising a small stretch of the damaged strand containing multiple bases surrounding the lesion, making it particularly efficient at dealing with extensive damage that may affect more than one nucleotide.

On the other hand, BER is more focused on correcting small-scale damage, such as single base modifications that are often the result of deamination or oxidative stress. It targets one base at a time rather than larger sections of DNA.

By understanding that NER addresses multiple base damages and can effectively correct larger, more complex lesions, you can appreciate why this is a defining feature of the mechanism. This understanding also highlights the specificity of DNA repair mechanisms in maintaining genomic integrity across different types of damage.