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, which may have lost its activity or functionality, could lead to incomplete or improperly repaired DNA, resulting in the accumulation of errors in the DNA. This may cause mutations, genomic instability, or other unwanted consequences.

Step-by-step solution

Understand the DNA repair systems

DNA repair systems are important in maintaining the genomic integrity of living organisms by correcting any errors or damages in the DNA. There are several repair mechanisms, one of them is the nucleotide excision repair (NER) system. NER works by detecting and removing a damaged section (lesion) of DNA and replacing it with the correct nucleotides through a series of steps: lesion recognition, incision and excision of the damaged nucleotides, DNA synthesis, and ligation.

Role of DNA ligase

DNA ligase is an enzyme that is responsible for joining two DNA ends or strands (nick) by creating phosphodiester bonds. It is essential for the completion of the NER process, as it joins the newly synthesized DNA strand with the original DNA strand, which restores the DNA molecule's continuity.

Expired DNA ligase

If the DNA ligase used in this scenario is expired, it's likely that the enzyme has lost its activity or functionality. In this case, the enzyme may not be able to perform its role in ligating the DNA strands.

Result of using expired DNA ligase

If the DNA ligase is inactive or less efficient, the consequence would be that the DNA repair process could be compromised, leading to incomplete or improperly repaired DNA. This may result in an accumulation of errors in the DNA, which could potentially lead to mutations, genomic instability, or other unwanted consequences. In summary, using expired DNA ligase in studying a DNA repair system like the nucleotide excision repair, would likely cause incomplete DNA repair due to the lack of proper ligation, which could compromise genomic integrity.