In this chapter, we focused on the translation of mRNA into proteins as well as on protein structure and function. Along the way, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations in the chapter, what answers would you propose to the following fundamental questions: How do we know, based on studies of Neurospora nutritional mutations, that one gene specifies one enzyme?

Video transcript

Hi everyone. Welcome back. Let's look at our next question. It says in the beetle and tatum experiment on euros for a the induced mutant was unable to synthesize which of the following when grown on minimal medium. So let's recall from our content video that beadle and tatum were exploring the theorized connection between the information in genes and enzymes that performed metabolic functions. Who puts up here? They theorized that if genes were connected to enzymes it should be possible to induce mutations in genes that would break a specific enzyme needed for growth in minimal media. So we recall that the reason they chose Norris Pora is that neuroscience can synthesize its own amino acids and most vitamins so it can grow in what's called minimal media containing only sugars, salts and a single vitamin. Um since it can synthesize everything else it needs, it can also grow in complete media that has added amino acids and vitamins but it doesn't need it if everything is working fine. But their thought was they could actually induce gene mutations that might prevent it from synthesizing one of those things that needs thus preventing it from being able to grow on that minimal media. So let's just look real briefly at a diagram of their experiment again, remembering that we're trying to remember what when they induced that mutant in that experiment to test this, what was the neuro sparrow? Unable to synthesize. So they started by radiating a sample of your ISP aura and then growing it in complete media. After it grew enough, they transferred it to minimal media knowing that if they saw no growth, they had a nutritional mutant, it was missing something they'd broken something needed to synthesize one of its essential nutrients. So they then transferred those samples that had not grown in the minimal media and took them and grew them in two different types of minimal media with additions. And we'll just put this up here. So having identified their nutritional mutants, they would grow some on minimal medium with amino acids added, but no vitamins. Then alternatively some of that nutritional mutant, they would grow on minimal medium plus vitamins, but no amino acids. So if the sample grew on this minimal medium with vitamins but no amino acids, then they would know that the defect was in the vitamin pathway. It could still synthesize all the amino acids that needed, but not vitamins, it needed the vitamins added to the medium. Conversely, if it grew in the um the minimal media with added amino acids, they knew that the defect was in the amino acid pathway. Well, they had to continue this a little further because there's 20 different amino acids. So what they then did after that was, they grew in 20 samples, 20 different samples of minimal medium with each one with a different amino acid added and then the growth identified which amino acid pathway was defective because it would only grow in the sample that had the amino acid added, that it couldn't synthesize for itself. And in the case of their initial experiment, um what they found was that their mutant they had induced was defective in the pathway to synthesize the amino acid arginine. So that's an amino acid. So we're going to go ahead and choose choice A they're induced mutant was unable to synthesize one of the amino acids When they did that experiment, see you in the next video.