Question

Several haploid strains of Saccharomyces cerevisiae grow well on YPD but do not grow on minimal media unless adenine is added to the minimal media. Some of those strains accumulate a red pigment and, thus, produce red or pink colonies. How would you determine the biochemical pathway that is defective in these yeast strains? How would you assign the functions to the genes that are mutated in these strains?

Answer 1

YPD or yeast extract-peptone-dextrose media remains one of the most widely used medium for yeast-growth in laboratory conditions. This medium contains all the necessary nutrients for the wild type yeasts to grow.

According to the information, the yeast cells fail to grow unless adanine has been added to the YPD. This suggests that the yeast strain so used is auxotroph in nature.

Secondarily, the information suggests that some of the yeast cells produce pink colonies due to accumulation of a red pigment. Studies have shown that the adenine-biosynthetic pathway leads to accumulation of gene product from gene ade2 thus leading to generation of a red pigment. The appearance of this red pigment is indicative that the cells have acclimatized to the environment of the growth medium and can be further used for experimentation.

In order to analyse the biochemical pathway behind this appearance of red/pink colonies, the adenine-biosynthesis can be investigated in pink/red and white colonies by using analytical methods.

Thus, the gene ade2 might have undergone mutation in these some yeast cells which prompted them to use the adenine present in the growth medium to conduct adenine biochemical pathway and hence accumulate the pigment.