Question

What is the proper order of the steps involved in nucleotide excision repair?

1 - Release of the damaged DNA segment between the incisions
2 - Sealing of strand by DNA ligase
3 - Lesion recognition
4 - Separation of the duplex's two strands in the region of the lesion in preparation for its removal.
5 - Filling of gap by DNA polymerase
6 - Binding of the XPB and XPD subunits of TFIIH to DNA in the region of the lesion
7. - Cutting of the damaged strand on both sides of lesion by endonucleases
a. 6 - 3 - 4 - 7 - 1 - 5 - 2
b. 3 - 6 - 4 - 7 - 1 - 2 - 5
c. 3 - 6 - 7 - 4 - 1 - 5 - 2
d. 3 - 6 - 4 - 7 - 1 - 5 - 2
e. 6 - 3 - 7 - 4 - 2 - 1 - 5

Answer 1

The correct order for the steps of nucleotide excision repair is recognition of the lesion, binding of repair factors to the DNA, unwinding and cutting of the damaged DNA, gap-filling by DNA polymerase, and sealing by DNA ligase, represented as option (d): 3 - 6 - 4 - 7 - 1 - 5 - 2.

Step-by-step explanation:

The proper order of the steps involved in nucleotide excision repair (NER) is option (d): 3 - 6 - 4 - 7 - 1 - 5 - 2. In this sequence, the process begins with the recognition of the lesion (step 3), followed by the binding of the XPB and XPD subunits of TFIIH to DNA in the region of the lesion (step 6). Next, the separation of the duplex's two strands in the region of the lesion is prepared for its removal (step 4), and then the cutting of the damaged strand on both sides of the lesion by endonucleases occurs (step 7). After the release of the damaged DNA segment between the incisions (step 1), the gap is filled by DNA polymerase (step 5). Finally, the process is completed with the sealing of the strand by DNA ligase (step 2).