Using your knowledge of DNA repair pathways, choose the pathway that would be used to repair the following types of DNA damage. Explain your reasoning.
A double-strand break that occurs just after replication in an actively dividing cell

Verified step by step guidance

1. Identify the type of DNA damage described in the problem. A double-strand break (DSB) is a severe form of DNA damage where both strands of the DNA helix are broken. This type of damage can lead to genomic instability if not repaired properly.
2. Consider the context of the damage. The problem specifies that the double-strand break occurs just after replication in an actively dividing cell. This is important because the cell has recently duplicated its DNA, meaning sister chromatids are available.
3. Recall the DNA repair pathways available for double-strand breaks. The two primary pathways are non-homologous end joining (NHEJ) and homologous recombination (HR). NHEJ directly joins the broken ends but is error-prone, while HR uses a homologous sequence (such as a sister chromatid) as a template for accurate repair.
4. Determine which pathway is most likely to be used in this scenario. Since the damage occurs just after replication, sister chromatids are present and can serve as templates for homologous recombination. HR is preferred in this case because it ensures high-fidelity repair by using the sister chromatid.
5. Explain the reasoning. Homologous recombination is the most suitable pathway for repairing double-strand breaks in actively dividing cells with sister chromatids available. This ensures accurate repair and prevents mutations or chromosomal rearrangements that could arise from error-prone repair mechanisms like NHEJ.

Key Concepts

Double-Strand Breaks (DSBs)

Double-strand breaks are severe forms of DNA damage where both strands of the DNA helix are broken. These breaks can lead to genomic instability if not repaired properly. DSBs can occur due to various factors, including ionizing radiation, chemical agents, or during DNA replication. Understanding the nature of DSBs is crucial for identifying the appropriate repair mechanisms.

Homologous Recombination (HR)

Homologous recombination is a DNA repair pathway that accurately repairs double-strand breaks using a homologous sequence as a template. This process is particularly active in dividing cells, especially after DNA replication when sister chromatids are available. HR is essential for maintaining genomic integrity and preventing mutations, making it the preferred method for repairing DSBs that occur shortly after replication.

Non-Homologous End Joining (NHEJ)

Non-homologous end joining is a DNA repair mechanism that directly ligates the broken ends of DNA without the need for a homologous template. This pathway is faster and often used in non-dividing cells or when homologous sequences are not available. While NHEJ is crucial for quick repairs, it can lead to insertions or deletions, making it less accurate than homologous recombination, especially in actively dividing cells.