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.
Heavily damaged bacterial DNA

Verified step by step guidance

1. Understand the context: Heavily damaged bacterial DNA often involves widespread damage that cannot be repaired by standard, high-fidelity repair mechanisms. This type of damage may include double-strand breaks, bulky adducts, or extensive base modifications.
2. Identify the appropriate repair pathway: For heavily damaged bacterial DNA, the SOS response is typically activated. This is a global response to DNA damage in bacteria that induces the expression of multiple DNA repair genes, including those involved in translesion synthesis (TLS).
3. Explain the reasoning: The SOS response allows the cell to bypass lesions that block replication by using specialized DNA polymerases (e.g., Pol IV and Pol V) that can synthesize DNA across damaged templates. While this process is error-prone, it ensures that replication can continue, which is critical for cell survival under extreme damage conditions.
4. Discuss the trade-offs: The error-prone nature of the SOS response can lead to mutations, but this trade-off is necessary for the survival of the bacterial cell when the DNA damage is too extensive for high-fidelity repair mechanisms like base excision repair (BER) or nucleotide excision repair (NER).
5. Conclude with the pathway choice: The SOS response is the most suitable pathway for repairing heavily damaged bacterial DNA because it provides a mechanism to tolerate and bypass extensive DNA damage, ensuring the continuation of replication and cell survival.

Key Concepts

DNA Repair Pathways

DNA repair pathways are cellular mechanisms that identify and correct damage to the DNA molecule. These pathways are crucial for maintaining genomic stability and preventing mutations that could lead to diseases such as cancer. Different types of damage, such as single-strand breaks, double-strand breaks, and base modifications, are repaired by specific pathways, including nucleotide excision repair, base excision repair, and homologous recombination.

SOS Response in Bacteria

The SOS response is a global response to DNA damage in bacteria, particularly in Escherichia coli. When DNA is heavily damaged, the SOS response is activated, leading to the expression of several genes involved in DNA repair and mutagenesis. This pathway allows bacteria to tolerate and repair extensive DNA damage, often through error-prone repair mechanisms that can introduce mutations but also enable survival under stress.

Homologous Recombination

Homologous recombination is a precise DNA repair mechanism that uses a homologous sequence as a template to repair double-strand breaks. This pathway is essential for maintaining genetic integrity, especially in organisms with complex genomes. In bacteria, homologous recombination can also facilitate the exchange of genetic material, contributing to genetic diversity and adaptation.