Concept 16 One gene makes one protein.

HI! You and your friend are going to use Neurospora to do mutant analysis. You get five mutant Neurospora strains (mutA-mutE) and five supplements (supA-supE) from Acme Mutants, Inc. Unfortunately, the booklet that tells you about the mutants and the synthesis pathway is missing. When you phoned Acme to ask about the synthesis pathway and the mutants, they weren't very helpful. They gave you the following information: 1) there are only five possible mutants in this synthesis pathway. 2) each strain is a different mutant in the same synthesis pathway. 3) the supplements complement the mutations for growth in minimal medium eg., supA for mutA etc. 4) mutE will grow if supplemented with supE, but also if supplemented with both supB and supD. The two of you decide to figure out the synthesis pathway yourselves. You make the minimal media tubes and test the mutants for their ability to grow with the various supplements. You decide to concentrate on mutA, mutC, and mutE first. You find that mutA can grow if supplemented with either supA or supE. It cannot grow when supplemented only with supC. Based on this information, you decide that: The order of the synthesis pathway is mutC, mutA, mutE. (That is correct) The order of the synthesis pathway is mutA, mutC, mutE. (No, mutA cannot grow if supC is added. mutA must occur after, or downstream, of mutC.) The order of the synthesis pathway is mutA, mutB, mutC. (No, we have not tested mutA with supB yet.) mutA grows if supE is added. Therefore, mutE must occur after, or downstream of, mutA. mutA cannot grow if supC is added. Therefore, mutC must occur before, or upstream of mutA. If this order is correct, then mutC will grow on minimal media if you add: supA. (mutC can grow if supA is added,but it can grow with other supplements.) supC. (mutC can grow if supC is added,but it can grow with other supplements. supE. (mutC can grow if supE is added, but it can grow with other supplements.) supA or supC or supE. (That is correct) Nothing. No supplements needed. (No, the correct supplements are needed for growth.) mutC can grow if supA or supC or supE are added to the minimal media. mutA and mutE act downstream of mutC. You still have to account for the mutant strains mutB and mutD. You test the mutants; mutB needs supB, and mutD needs supD to grow. You test mutE with supB and supD, and sure enough, mutE can grow on minimal media if both supB and supD are added. Does this mean that mutC and mutA will also grow on minimal media if both supB and supD are added? Yes. (That is correct.) No. (No, mutE is downstream. If mutE can grow with supB and supD, then so can mutC and mutA.) mutC can grow but mutA cannot. (No, mutE is downstream of mutC and mutA. If mutE can grow with supB and supD, then so can mutC and mutA.) mutA can grow but mutC cannot. (No, mutE is downstream of mutC and mutA. If mutE can grow with supB and supD, then so can mutC and mutA.) mutE is downstream of mutC and mutA. If mutE can grow with supB and supD, then so can mutC and mutA. Based on your results, all the mutants mutA-mutE can grow on minimal media if you supplement with both supB and supD. This means that: supB is the precursor molecule used to make supD. (No, if supB is a precursor, then mutB would only need supD to grow. mutB needs both supB and supD.) supD is the precursor molecule used to make supB. (No, if supD is a precursor, then mutD would only need supB to grow. mutD needs both supB and supD. ) supB and supD are the end products of this synthesis pathway. (That is correct) supB and supD are the precursor molecules used to make all the other molecules in this synthesis pathway. (No, since the mutants can be rescued using supB and supD, then these cannot be precursors.) All of the mutants can grow on minimal media if supB and supD are added. Therefore, both supB and supD are the end products of this synthesis pathway. cONGRATULATIONS!!! YOU'RE SO SMART!