You are working with a strain of the common laboratory organism Pichia pastoris, a unicellular yeast. You note that this particular strain will not grow on media when it lacks valine. However, when you provide the yeast with threonine-ammonia lyase, the first enzyme in the valine biosynthesis pathway, it grows on media lacking valine. This suggests that A) valine is not an essential amino acid for Pichia pastoris. B) there is a mutation in the gene encoding threonine-ammonia lyase in the yeast. C) there is a mutation in the last step of the valine biosynthesis pathways. D) there is a mutation in a middle step of the valine biosynthesis pathways. E) there is a mutation in the valine biosynthesis pathway but it is not possible to say where.

Question

Quizplus · Accepted Answer

The yeast's inability to grow on media lacking valine suggests it cannot synthesize valine on its own. However, when provided with threonine-ammonia lyase, the first enzyme in the valine biosynthesis pathway, it can grow, indicating a likely mutation in the gene encoding this enzyme, preventing its normal production.

You Are Working with a Strain of the Common Laboratory