Question

Benzo[a]pyrene, the cancer-causing agent in cigarette smoke, is a powerful mutagen. Benzo[a]pyrene itself is relatively harmless, but it is metabolized in the liver to produce active molecules that react covalently with DNA. In an experiment, benzo[a]pyrene is incubated with a mixture of liver enzymes to form its genotoxic metabolites. These metabolites are added to E. coli cells that have a mutation in a gene encoding an enzyme of the serine-synthesizing pathway (i.e., the cells are serine auxotrophs, requiring serine for growth). When the treated cells are grown on serine-containing medium, the results show that the benzo[a]pyrene metabolites kill cells in a dose-dependent manner. When treated and untreated serine-auxotrophic cells are plated separately on serine-free media, the cells treated with benzo[a]pyrene metabolites show a 10- to 100-fold increase in survivors compared with untreated cells. Explain these results.Compare and contrast mismatch repair in E. coli and eukaryotes.

List two reasons translesion sysnthesis tends to be mutagenic.

Describe, in detail, nucleotide excision repair. Include especially ways the damage can be recognized.