Question

Clinical data support the link between smoking/chewing tobacco and cancer. An Ames test showed that trp- E. coli always grows in the presence of tobacco juice. Give two possible explanations for this Ames test outcome. In your answers you may use acronyms instead of full names of molecules/proteins, just explain their names.

Answer 1

Ames test is used to find out whether a mutagen causes a mutation or not. Here, the mutagen is tobacco juice. The Salmonella strain used in Ames test is his-, i.e. it requires Histidine for growth.

Tryptophan is an essential amino acid. Generally, E.coli has tryptophan operon which regulates tryptophan levels. Here, "trp^-E.coli" is capable of growth in presence of tobacco juice. This means that tobacco juice destroys the essential amino acid (trp) so that E.coli can grow easily in this environment.

Another explanation will be that tobacco juice is a mutagen. It converts trp^-E.coli into trp⁺; now trp⁺ converts his^- to his⁺; this will result into positive Ames test-------> E. coli capable of growth in this environment ------> colonies formed.

The second explanation is more promising according to Ames test.