Question

You identify an auxotroph that doesn't grow in normal medium, but does grow in medium supplemented with Q, indicating that it has a defect in one or more enzymes in this pathway. This auxotroph is also able to grow if you supplement the medium with Y. Based on this, which enzymes can you say with certainty is/are disrupted by the mutation

Answer 1

Answer: Enzymes in both Q and Y pathway are disrupted because you have to supplement the medium with those components for the organism to grow.

Explanation:

A microorganism is auxotrophic when it is only able to proliferate in a culture medium if some specific substance has been added to it, which the wild type (prototroph) does not require, because it can synthezise it. The underlying genetics of auxotrophy is the lack of a functional metabolic pathway that generates the substance on which the auxotroph depends. This lack is usually due to a mutation that generates a null allele lacking biological capacity. So, due to a deficiency in an enzyme required for the synthesis of a certain component, the organism requires that component in the culture medium in order to grow.

A metabolic pathway is a set of consecutive chemical reactions catalyzed by enzymes synthesized by the cell, in which the product of one is the substrate of another. In living organisms there are multiple metabolic pathways, responsible for synthesizing and metabolizing compounds (cellular components, regulatory molecules, compounds that serve to store energy), or degrading them to obtain energy. Thus, enzymes catalyze chemical reactions, this means they accelerate the rate of reaction.

A normal medium is one that possesses all the nutrients and compounds necessary for the proper functioning of a normal organism (prototroph). However, if the organism lacks, for example, an enzyme, it will not grow in a normal medium because it does not have the enzyme to make the components. If the organism does not grow in the normal environment, then it has some mutation that causes some enzyme not to be produced. Remember that enzymes are proteins, and all proteins are encoded by DNA, so if there is a mutation in the DNA, in the gene that encodes the enzyme, the enzyme will not be synthesized or will be synthesized but in such a way that it cannot function properly.

If the organisms only grow in medium supplemented with Q and in medium supplemented with Y, then this indicates that it has a defect in one or more enzymes in Q and Y pathway, because the organism cannot produce certain components and they need to be added in the environment. The problem does not provide enough information to know if for each pathway only one enzyme is affected or several, but it is enough to say that enzymes in both Q and Y pathway are disrupted because you have to supplement the medium with those components for the organism to grow.