Question

Suppose you are studying a DNA repair system, such as the nucleotide excision repair in vitro. By mistake, you add DNA ligase from a tube that has already expired. What would be the result?

Short answer

Answer: Using expired DNA ligase in a nucleotide excision repair system in vitro could lead to incomplete or erroneous ligation of the repaired DNA segment. This may result in further DNA damage, interference with normal cellular processes like replication or transcription, and potentially harmful consequences for the cell.

Step-by-step solution

Understand nucleotide excision repair

Nucleotide excision repair (NER) is a DNA repair system that identifies and repairs damaged DNA by removing the damaged piece of DNA and then synthesizing a new, correct piece of DNA that replaces it. The process consists of several steps, including damage recognition, strand opening, damaged strand removal, DNA synthesis, and ligation.

Understand the role of DNA ligase

DNA ligase is an enzyme that plays a crucial role in the ligation step of the NER process, where it facilitates the joining of DNA strands (in this case, the repair patch) by forming a phosphodiester bond between the 3’-hydroxyl end of one nucleotide and the 5’-phosphate end of another nucleotide. Thus, DNA ligase ensures the continuity and stability of the newly synthesized DNA.

Analyze the effect of using expired DNA ligase

If the DNA ligase used in the nucleotide excision repair system in vitro is expired, it might lose its enzymatic activity or functions due to denaturation or degradation. This could potentially lead to incomplete or erroneous ligation of the repaired DNA strand.

Determine the consequences of incomplete or erroneous ligation

The consequences of an incomplete or erroneous ligation of the repaired DNA segment may lead to the DNA strand remaining broken or having errors in the repaired region. This might result in further DNA damage, which could propagate as mutations or interfere with normal cellular processes like replication or transcription, ultimately causing the repaired DNA sequence to be nonfunctional or potentially harmful to the cell.

Conclusion

In conclusion, adding expired DNA ligase in the nucleotide excision repair in vitro system would likely lead to incomplete or erroneous ligation of the repaired DNA segment. This can cause further DNA damage, affect normal cellular processes, and potentially have harmful consequences for the cell.