Experiments conducted by Charles Yanofsky in the 1950s and 1960s helped characterize the nature of tryptophan synthesis in E. coli. In one of Yanofsky's experiments, he observed that a mutation in the gene caused premature termination of translation due to a stop codon at position 243. Which of the following base-pair substitutions could result in a stop codon at position 243 of tryptophan synthetase?

Escherichia coli bacterial culture undergoes exposure to ultraviolet (UV) radiation. Subsequently, the bacterial cells are cultivated on a complete medium, and 8 individual colonies (numbered 1 to 8) are chosen for further analysis. The complete medium plate is used to create four replica plates, which contain minimal medium or minimal medium added with one antibiotic (replica plates numbered 1 to 4). The results obtained are as follows:

Can you identify the colony or colonies that exhibit resistance to all the tested antibiotics?

The auxotrophic selection method is a genetic research technique used to select and isolate cells with a specific genetic mutation by growing mutant cells on a medium that lacks an essential nutrient that the mutant cells cannot produce. Can you identify the colonies that are his⁻, arg⁻, leu⁻ using this method?

Cyanobacteria were found to have been experiencing a high rate of mutation due to chemical pollution caused by an oil spill. Researchers perform mutagenesis assays using various known mutagens. The results show that the highest rate of reversion occurs when the bacteria are exposed to UV radiation.
Which of the following statements is therefore true about the impact of the oil spill on cyanobacteria?

Tobacco-specific nitrosamines and drugs such as streptozotocin can adversely impact the DNA. What type of DNA lesions can result from taking these compounds?

Which of the following pathways is responsible for repairing helix-distorting DNA damage?

The Chernobyl accident triggered the release of radioactive iodine (I¹³¹) into the environment. This radioactive contaminant caused an increased risk of cancer and other health-related problems among the exposed population. Which of the following is considered one of the main consequences of radioactive iodine exposure?