The graph that follows shows the survival of four different E. coli strains after exposure to increasing doses of ultraviolet light. The wild-type strain is normal, but the other strains have a mutation in either a gene called uvrA, a gene called recA, or both.

(b) What are the relative contributions of these genes to the repair of UV damage?

Verified step by step guidance

1. Observe the graph which shows the survival rate of four E. coli strains after exposure to increasing doses of UV light. The strains include wild-type, uvrA mutant, recA mutant, and uvrA and recA double mutant.
2. Note that the wild-type strain maintains a high survival rate across all doses of UV light, indicating effective repair mechanisms for UV-induced damage.
3. The uvrA mutant shows a significant decrease in survival as the UV dose increases, suggesting that the uvrA gene plays a crucial role in repairing UV damage.
4. The recA mutant also shows a decrease in survival, but it is less severe than the uvrA mutant, indicating that recA contributes to repair but is not as critical as uvrA.
5. The double mutant (uvrA and recA) has the lowest survival rate, demonstrating that both genes are important for UV damage repair, with uvrA having a more pronounced effect than recA.

Key Concepts

DNA Repair Mechanisms

DNA repair mechanisms are essential cellular processes that correct damage to the DNA molecule. In bacteria like E. coli, these mechanisms include nucleotide excision repair and recombinational repair, which help maintain genomic integrity after exposure to damaging agents such as ultraviolet (UV) light. Understanding these mechanisms is crucial for analyzing how different strains of E. coli respond to UV-induced damage.

uvrA Gene

The uvrA gene encodes a protein that is part of the nucleotide excision repair pathway, which recognizes and removes bulky DNA lesions caused by UV light. Mutations in the uvrA gene can impair the cell's ability to repair UV-induced damage, leading to increased cell death when exposed to UV radiation. This gene's role is critical in understanding the survival rates of different E. coli strains under UV exposure.

recA Gene

The recA gene is vital for homologous recombination and DNA repair in bacteria. It facilitates the repair of DNA double-strand breaks and is involved in the SOS response, which is activated in response to extensive DNA damage. Mutations in the recA gene can significantly affect a cell's ability to survive UV damage, making it important to analyze its contribution alongside the uvrA gene in the context of the experiment.