Analysis To better understand today\'s experiment, i will be helpt al to eir ona

Question

Analysis To better understand today's experiment, i will be helpt al to eir ona closer look at the experiment that led Beadle and Tatum to their One nzyme hypothesis. They chose the bread mold Neurospora because it can grow en provided with minimal media containing only inorganic salts, simple sugar, and otun. For this reason, wild-type Neurospora is considered a prototroph because it can Synthesize everything it needs to grow (amino acids, other vitamins, nucleic acids, etc) rom a minimal media. Neuorspora strains that fail to grow in minimal media are unable to synthesize a necessary ingredient required for growth and are auxotrophs. Beadle and Tatum created mutant strains and found several auxotrophs that could only grow on minimal media if it was supplemented with arginine. Therefore, they reasoned that these arginine auxotrophs carried mutations that blocked arginine biosynthesis. Through genetic analysis they found that each mutant corresponded to a different gene, meaning that the biosynthesis of arginine was under genetic control and required 4 separate genes. They hypothesized a linear pathway in which each intermediate in the pathway was a product of the previous step and the substrate for the next step. The arginine biosynthetic pathway is shown below. The table provides results from Beadle and Tatum's experiment where auxotrophs were recovered and testing resulted in Growth (+) or No Growth (-) in minimal media with or without specified supplements. The four mutants tested are auxotrophs Gene- One E bi with a defect in a specific step of the pathway 1. Identify the step in the pathway that is defective in each mutant Winimal Omithine Citruline Arginino Arginine Meda Mutant 1 Mutant 2 Mutant 3 Mutant 4 Mutant #- Ho HO NH2 NH2 #24 HO ornithine argininosuccinate arginine BIO 376 Genetics Laboratory inter 2018

Explanation / Answer

N-Acetylornithine --(1st step)--> Ornithine --(2nd step)--> Citrulline --(3rd step)--> Argininosuccinate --(4th step)--> Arginine

Mutant 4 can grow if you provide any of the last four intermediates. So, it catalyzes the first step.
Mutant 1 can grow if you provide any of the last three intermediates. So, it catalyzes the second step.
Mutant 2 can grow if you provide any of the last two intermediates. So, it catalyzes the third step.
Mutant 3 can grow if you provide only the last intermediates. So, it catalyzes the last step.

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