Question

If a mutation eliminated the function of UvrC, which aspect of the nucleotide excision repair system would not work? a. sensing a damaged DNA site b. endonuclease cleavage of the damaged strand c. removal of the damaged strand d. synthesis of a new strand, using the undamaged strand as a template e. none of the above

Short answer

The aspect of the nucleotide excision repair system that would not work if a mutation eliminated the function of UvrC is b. endonuclease cleavage of the damaged strand.

Step-by-step solution

Understanding UvrC function

The first step is to understand the function of UvrC. UvrC is an endonuclease involved in the excision repair of DNA with a role in incising the DNA strand on the 5' side of the lesion.

Mapping UvrC function to given options

The second step is to match the function of UvrC with the provided options. Based on our understanding from step 1, UvrC function is tied with incision or cleavage of the dna strand at the damage site. So we map this function to the provided options.

Selecting the right option

Based on the UvrC role description in step 1 and the processing in step 2, we can see that option b. 'endonuclease cleavage of the damaged strand' corresponds to the role of UvrC in the DNA repair process. Therefore, if a mutation eliminated the function of UvrC, the endonuclease cleavage of the damaged strand would not work.

Key concepts

Nucleotide Excision Repair System

The nucleotide excision repair system (NER) is a vital DNA repair mechanism that detects and remedies a wide variety of DNA lesions, especially those affecting the overall shape of the DNA helix. When DNA is damaged by ultraviolet light or chemicals, the damage can cause the DNA structure to become distorted.

The NER pathway consists of several critical steps to restore the DNA to its original state. Initially, the damage is recognized by sensor proteins. Following damage recognition, a couple of incisions are made on either side of the damage site by specific enzymes called endonucleases. The segment of the DNA containing the lesion is then removed, and the gap is filled in using the undamaged strand as a template by DNA polymerases. Finally, DNA ligase seals the new strand to the existing DNA, completing the repair.

Endonuclease Cleavage

Endonuclease cleavage is a process where enzymes called endonucleases recognize and cut damaged sites within a DNA strand. This cleavage is critical during the DNA repair process, particularly in the nucleotide excision repair system.

In this system, endonucleases make precise cuts on both the 5' and 3' ends of the damaged DNA segment. Proteins such as UvrB and UvrC form a complex to perform this incision. UvrC specifically is responsible for incisions at the 5' side of the lesion. It is imperative for the nucleotide excision repair process, as without these incisions, the damaged DNA cannot be removed and consequently, cannot be replaced with the correct sequences.

DNA Repair Process

The DNA repair process is a series of actions taken by a cell to identify and correct damage to the DNA molecules that encode its genome. Various types of damage to the DNA can happen due to environmental factors, such as ultraviolet light and radiation, or from internal factors like reactive oxygen species.

DNA repair ensures the survival of a cell and prevents mutations, which can lead to disease, including cancer. There are several different DNA repair mechanisms in a cell, including nucleotide excision repair, base excision repair, and mismatch repair, each dealing with specific types of DNA damage.

Mutation Impact on DNA Repair

Mutations in DNA repair genes can have significant consequences on the DNA repair process. When a mutation affects a repair protein, such as UvrC, it alters the cell's ability to fix certain types of DNA damage.

For instance, if a mutation eliminates the function of UvrC, the endonuclease cleavage step in the nucleotide excision repair system would be hindered. Without proper cleavage, the damaged DNA segment would remain in place, leading to faulty replication and transcription. This could potentially result in mutations that may cause cell death or lead to diseases like cancer. Understanding the role of each repair component is therefore critical for comprehending the broader implications of DNA repair on cell health and function.