WEBVTT 00:00:00.000 --> 00:00:03.040 Welcome, everyone, to today's Deep Dive. I am 00:00:03.040 --> 00:00:05.240 so glad you, the learner, are joining us because 00:00:05.240 --> 00:00:08.119 we have a truly mind -bending journey today. 00:00:08.220 --> 00:00:09.900 Yeah, we really do. I'm excited for this one. 00:00:10.060 --> 00:00:13.419 So we are pulling from a fascinating encyclopedia 00:00:13.419 --> 00:00:16.579 entry on something known as the one gene one 00:00:16.579 --> 00:00:19.660 enzyme hypothesis. Which, I mean, it sounds super 00:00:19.660 --> 00:00:21.719 academic right off the bat, but the story behind 00:00:21.719 --> 00:00:24.800 it is wild. It really is. Our mission for this 00:00:24.800 --> 00:00:28.000 deep dive is to explore how a seemingly simple 00:00:28.140 --> 00:00:30.879 almost bizarre little experiment on humble bread 00:00:30.879 --> 00:00:34.000 mold became the opening gun of molecular biology. 00:00:34.619 --> 00:00:36.840 It completely revolutionized how we understand 00:00:36.840 --> 00:00:39.159 our own DNA. Right. It laid the groundwork for 00:00:39.159 --> 00:00:41.200 literally everything we know about genetics today. 00:00:41.479 --> 00:00:44.200 Exactly. OK, let's unpack this, because to understand 00:00:44.200 --> 00:00:46.560 how huge this was, we kind of have to rewind 00:00:46.560 --> 00:00:48.899 the clock. Yeah, I want you to really step into 00:00:48.899 --> 00:00:51.520 the scientific mindset of the early 20th century, 00:00:51.640 --> 00:00:54.020 like leading up to the mid 1930s. When things 00:00:54.020 --> 00:00:56.560 were very different. Very different. Scientists 00:00:56.560 --> 00:00:59.719 knew genes existed, obviously, but the prevailing 00:00:59.719 --> 00:01:02.159 consensus was that genes only controlled, you 00:01:02.159 --> 00:01:04.799 know, trivial things. Superficial stuff. Right. 00:01:05.280 --> 00:01:08.420 Like eye color or the specific way bristles grew 00:01:08.420 --> 00:01:10.719 on the back of a fruit fly. They were basically 00:01:10.719 --> 00:01:13.040 viewed as biological decorators. Just picking 00:01:13.040 --> 00:01:15.500 out the drapes and the paint colors. Exactly. 00:01:16.219 --> 00:01:18.540 Meanwhile, they thought the real heavy lifting, 00:01:18.680 --> 00:01:21.040 the life sustaining biochemistry and metabolism. 00:01:21.659 --> 00:01:24.120 was just happening mysteriously in the cell's 00:01:24.120 --> 00:01:26.459 cytoplasm. Completely divorced from genetics. 00:01:26.560 --> 00:01:29.120 Totally siloed. Genetics was over here, metabolism 00:01:29.120 --> 00:01:32.659 was over there. Now, there were a few early hints 00:01:32.659 --> 00:01:35.319 that they were connected, like back in 1902. 00:01:35.420 --> 00:01:39.159 Oh yeah, Archibald Garrod. Yes. A physician who 00:01:39.159 --> 00:01:41.819 identified a human condition called alkaptenuria. 00:01:42.299 --> 00:01:44.579 Right, which is basically an error in metabolism 00:01:44.579 --> 00:01:47.260 where the body can't process certain amino acids. 00:01:47.299 --> 00:01:49.540 Right, and it results in very dark urine. Right. 00:01:49.689 --> 00:01:52.810 But the key thing Garrett noticed was that this 00:01:52.810 --> 00:01:55.170 condition followed Mendelian recessive inheritance 00:01:55.170 --> 00:01:57.849 patterns. Meaning it was passed down through 00:01:57.849 --> 00:02:00.150 families exactly like a genetic trait, even though 00:02:00.150 --> 00:02:02.549 it was a metabolic disorder. Exactly. That was 00:02:02.549 --> 00:02:04.730 the crucial link. But honestly, the scientific 00:02:04.730 --> 00:02:07.049 community largely just ignored the implications 00:02:07.049 --> 00:02:09.849 of his work for decades. Which is wild to think 00:02:09.849 --> 00:02:13.110 about. It is. Through the late 1930s, researchers 00:02:13.110 --> 00:02:16.250 were just completely stuck on how to practically 00:02:16.250 --> 00:02:19.169 apply genetics to metabolism. which takes us 00:02:19.169 --> 00:02:21.830 right inside the legendary Caltech laboratory 00:02:21.830 --> 00:02:24.870 of Thomas Hunt Morgan in the mid -1930s. A very 00:02:24.870 --> 00:02:27.629 famous lab. Very famous. And this is where we 00:02:27.629 --> 00:02:30.449 meet two geneticists, Boris Afrusi and George 00:02:30.449 --> 00:02:32.689 Beadle. They were basically spending their days 00:02:32.689 --> 00:02:35.930 staring at Drosophila melanogaster. The classic 00:02:35.930 --> 00:02:38.430 laboratory fruit fly. Right. And they were heavily 00:02:38.430 --> 00:02:40.810 focused on the eye color pigments of these flies. 00:02:40.909 --> 00:02:43.330 Yeah. And through their observations, they noticed 00:02:43.330 --> 00:02:46.439 this critical pattern. The genes affecting eye 00:02:46.439 --> 00:02:49.060 color appear to be serially dependent. Meaning 00:02:49.060 --> 00:02:52.020 what, exactly? Well, the normal bright red eyes 00:02:52.020 --> 00:02:54.800 of a wild fruit fly weren't just created by a 00:02:54.800 --> 00:02:58.020 single bucket of red biological paint. That red 00:02:58.020 --> 00:03:00.620 color was the final product of precursor pigments 00:03:00.620 --> 00:03:03.460 going through a whole series of sequential chemical 00:03:03.460 --> 00:03:06.099 transformations. Oh, like an assembly line. Exactly 00:03:06.099 --> 00:03:08.289 like an assembly line. And different genetic 00:03:08.289 --> 00:03:10.330 mutations disrupted these transformations at 00:03:10.330 --> 00:03:13.469 very specific points. So Betel looks at this 00:03:13.469 --> 00:03:16.610 serial dependence and reasons that each gene 00:03:16.610 --> 00:03:18.949 must be responsible for an enzyme that acts at 00:03:18.949 --> 00:03:21.990 a specific step in this pathway. Right. And what's 00:03:21.990 --> 00:03:24.729 fascinating here is the sheer historical bottleneck 00:03:24.729 --> 00:03:28.069 these researchers faced. Betel had the intuition. 00:03:28.550 --> 00:03:30.949 He knew the genes were somehow disrupting these 00:03:30.949 --> 00:03:33.650 pigment transformations. But he couldn't prove 00:03:33.650 --> 00:03:35.939 it. He couldn't prove a universal biological 00:03:35.939 --> 00:03:39.300 rule because the fruit fly eye is just incredibly 00:03:39.300 --> 00:03:42.219 complex. Yeah, the sources made it sound like 00:03:42.219 --> 00:03:44.759 extracting those intermediate fly eye pigments 00:03:44.759 --> 00:03:47.460 was just this overwhelmingly tedious physical 00:03:47.460 --> 00:03:49.580 process. Oh, it was a nightmare. I kept thinking 00:03:49.580 --> 00:03:52.259 about the sheer frustration of their daily lab 00:03:52.259 --> 00:03:54.919 work. It's honestly like trying to reverse engineer 00:03:54.919 --> 00:03:57.219 a complex secret recipe just by looking at the 00:03:57.219 --> 00:03:59.479 final baked cake. That is a great way to put 00:03:59.479 --> 00:04:01.879 it. Like you're scraping off tiny crumbs, trying 00:04:01.879 --> 00:04:03.819 to chemically guess what happened in the oven 00:04:03.819 --> 00:04:06.659 step by step. The end product is just too messy 00:04:06.659 --> 00:04:09.000 to work backward from. Yeah, that analogy hits 00:04:09.000 --> 00:04:11.169 the nail on the head. The underlying biochemical 00:04:11.169 --> 00:04:13.789 details were obscured by the sheer complexity 00:04:13.789 --> 00:04:16.589 of the multicellular organism. And to make matters 00:04:16.589 --> 00:04:19.709 worse, Betel ends up moving to Stanford University 00:04:19.709 --> 00:04:23.720 in 1937. teams up with a biochemist named Edward 00:04:23.720 --> 00:04:26.660 Tatum, and they get scooped. Oh, man, the ultimate 00:04:26.660 --> 00:04:29.240 scientific heartbreak. Truly. They actually had 00:04:29.240 --> 00:04:32.420 some initial success isolating one of those intermediate 00:04:32.420 --> 00:04:35.980 fly eye pigments. But another researcher, Adolf 00:04:35.980 --> 00:04:38.600 Buitenant, beat them to the official discovery 00:04:38.600 --> 00:04:40.660 and publication. So they are just completely 00:04:40.660 --> 00:04:42.759 defeated at this point. The flies are too tedious, 00:04:42.980 --> 00:04:45.139 the biochemistry is too messy, and they just 00:04:45.139 --> 00:04:47.420 lost a major race. They realized that trying 00:04:47.420 --> 00:04:50.579 to unweave the complex cake of a fruit fly was 00:04:50.579 --> 00:04:53.279 a dead end. They desperately needed an easier, 00:04:53.519 --> 00:04:55.680 faster organism to study. Which leads us to the 00:04:55.680 --> 00:04:59.040 real star of our deep dive. Yes, a humble, incredibly 00:04:59.040 --> 00:05:01.740 simple organism called Neurosporichrosa. Better 00:05:01.740 --> 00:05:04.560 known as bread mold. Bread mold. Another researcher 00:05:04.560 --> 00:05:07.379 from Morgan's orbit, Carl C. Lindegren, had recently 00:05:07.379 --> 00:05:09.860 been using this specific mold for genetic research. 00:05:10.060 --> 00:05:12.360 And Beadle and Tatum realized it was the absolute 00:05:12.360 --> 00:05:14.360 perfect subject. So for the listener wondering 00:05:14.360 --> 00:05:17.000 why on earth mold is biologically superior to 00:05:17.000 --> 00:05:19.399 a fruit fly, there are a few massive advantages 00:05:19.399 --> 00:05:22.319 here. Oh, totally. First, it required a very 00:05:22.319 --> 00:05:24.959 simple growth medium. So it was cheap and easy 00:05:24.959 --> 00:05:27.680 to keep alive. It grew incredibly fast, too. 00:05:27.800 --> 00:05:30.160 But the real game changer was how it reproduced. 00:05:30.680 --> 00:05:33.720 It produces these spores called ascospores. And 00:05:33.720 --> 00:05:36.199 the beauty of ascospores is that they are haploid. 00:05:36.439 --> 00:05:39.240 Yes, haploid is the key word here. Let me jump 00:05:39.240 --> 00:05:41.579 in on that because haploid is one of those textbook 00:05:41.579 --> 00:05:44.720 terms that can trip people up. Go for it. For 00:05:44.720 --> 00:05:47.759 you listening, haploid just means the mold only 00:05:47.759 --> 00:05:51.160 has one single set of chromosomes. Humans and 00:05:51.160 --> 00:05:53.720 fruit flies are diploid. We have two sets, one 00:05:53.720 --> 00:05:55.860 from each parent. Right, which creates a buffer. 00:05:56.220 --> 00:05:59.399 Exactly. If you have a mutated, broken gene on 00:05:59.399 --> 00:06:01.980 one chromosome, your body can usually just rely 00:06:01.980 --> 00:06:04.360 on the healthy backup copy from the other parent. 00:06:04.720 --> 00:06:07.420 the mutation stays hidden. But with haploid bread 00:06:07.420 --> 00:06:10.259 mold, there is no backup copy. None at all. If 00:06:10.259 --> 00:06:13.240 you mutate a gene, that mutation shows up immediately 00:06:13.240 --> 00:06:15.120 in the mold's behavior. Which made isolating 00:06:15.120 --> 00:06:18.500 genetic mutants incredibly easy and fast. So 00:06:18.500 --> 00:06:21.220 beetle and tatum have their perfect simple organism. 00:06:21.740 --> 00:06:24.019 And their methodology was just breathtakingly 00:06:24.019 --> 00:06:26.339 direct. Oh, it's brilliant. It's so brute force. 00:06:26.600 --> 00:06:29.790 It really is. To figure out how the mold's internal 00:06:29.790 --> 00:06:32.990 chemistry worked, they basically decided to completely 00:06:32.990 --> 00:06:35.689 break it. Wait, so they purposefully blasted 00:06:35.689 --> 00:06:38.410 mold with x -rays just to break it? Yes. They 00:06:38.410 --> 00:06:41.360 irradiated it. They were actively trying to create 00:06:41.360 --> 00:06:44.959 what biologists call oxotrophs. Oxotrophs. Right, 00:06:45.139 --> 00:06:47.720 which are mutant strains that have very specific 00:06:47.720 --> 00:06:50.139 metabolic defects. It's like taking the spark 00:06:50.139 --> 00:06:52.220 plugs out of a car engine to prove exactly what 00:06:52.220 --> 00:06:54.620 the spark plugs do. Exactly. So they irradiate 00:06:54.620 --> 00:06:57.139 the mold and then they test these broken biological 00:06:57.139 --> 00:06:59.319 car engines using two different types of food. 00:07:00.120 --> 00:07:02.420 A minimal medium and a complete medium. Yes. 00:07:02.879 --> 00:07:05.870 The genius is in the simplicity of this. A minimal 00:07:05.870 --> 00:07:08.490 medium has only the absolute bare -bones basic 00:07:08.490 --> 00:07:11.470 nutrients, like some salts, sugar, and one vitamin. 00:07:11.870 --> 00:07:14.629 And normal unmutated bread mold thrives on this, 00:07:14.769 --> 00:07:16.470 right? Totally, because its internal genetics 00:07:16.470 --> 00:07:19.170 and enzymes are perfectly capable of synthesizing 00:07:19.170 --> 00:07:21.769 everything else it needs to live. It builds all 00:07:21.769 --> 00:07:23.970 its own complex vitamins right from those basics. 00:07:24.189 --> 00:07:26.310 But a complete medium is like an all -you -can 00:07:26.310 --> 00:07:28.949 -eat biological buffet. It already contains all 00:07:28.949 --> 00:07:31.430 those complex vitamins and amino acids pre -made. 00:07:31.509 --> 00:07:34.899 So this gave them a perfect binary test. If the 00:07:34.899 --> 00:07:37.079 mold's internal assembly line was broken by the 00:07:37.079 --> 00:07:40.060 X -ray, if it was missing a crucial enzyme step, 00:07:40.540 --> 00:07:42.860 it would just die on the minimal medium. Because 00:07:42.860 --> 00:07:45.060 it couldn't manufacture its own nutrients anymore. 00:07:45.279 --> 00:07:47.720 Right, but that same broken mold would survive 00:07:47.720 --> 00:07:50.079 on the complete medium because the nutrient it 00:07:50.079 --> 00:07:52.100 couldn't make was already provided for it. They 00:07:52.100 --> 00:07:54.699 basically proved the engine was broken, but they 00:07:54.699 --> 00:07:56.939 didn't stop there, did they? No, they wanted 00:07:56.939 --> 00:07:59.560 to know exactly which spark plug they had smashed. 00:08:00.180 --> 00:08:02.560 So if a broken mutant couldn't grow on the minimal 00:08:02.560 --> 00:08:05.149 medium, they would start adding individual supplements 00:08:05.149 --> 00:08:08.029 to the petri dish, one by one. Just one amino 00:08:08.029 --> 00:08:11.310 acid, or just one specific vitamin. Exactly. 00:08:11.670 --> 00:08:13.709 And if the broken mold suddenly sprung back to 00:08:13.709 --> 00:08:16.629 life when they added, say, vitamin B6, they knew 00:08:16.629 --> 00:08:18.769 exactly which specific step in the biological 00:08:18.769 --> 00:08:20.829 assembly line the x -ray had destroyed. That 00:08:20.829 --> 00:08:24.009 is so elegant. By creating this series of related 00:08:24.009 --> 00:08:26.290 mutants, they literally determined the exact 00:08:26.290 --> 00:08:28.930 order in which metabolites and amino acids were 00:08:28.930 --> 00:08:32.080 synthesized within the cells. They proved, undeniably, 00:08:32.419 --> 00:08:34.899 that if a mutation disrupted the synthesis of 00:08:34.899 --> 00:08:38.059 a particular nutrient, adding that specific nutrient 00:08:38.059 --> 00:08:40.600 back in fixed the problem. And most mutations 00:08:40.600 --> 00:08:43.320 they isolated affected only a single metabolic 00:08:43.320 --> 00:08:46.419 pathway. It usually only blocked a single step 00:08:46.419 --> 00:08:48.799 within that pathway. So the obvious inference 00:08:48.799 --> 00:08:51.440 from this massive data set was that each gene 00:08:51.440 --> 00:08:54.299 mutation affects the activity of exactly one 00:08:54.299 --> 00:08:56.740 single enzyme. Which brings us to the historic 00:08:56.740 --> 00:09:01.470 AHA. moment. On November 15, 1941, Beadle and 00:09:01.470 --> 00:09:03.509 Tatum published a paper in the Proceedings of 00:09:03.509 --> 00:09:06.169 the National Academy of Sciences. A huge milestone. 00:09:06.529 --> 00:09:09.590 Monumental. They formally proposed that genes 00:09:09.590 --> 00:09:12.570 control or regulate specific reactions by either 00:09:12.570 --> 00:09:15.110 acting directly as enzymes or by determining 00:09:15.110 --> 00:09:17.450 the specificities of those enzymes. And just 00:09:17.450 --> 00:09:19.610 to close the loop on the terminology, a few years 00:09:19.610 --> 00:09:22.669 later in 1948, their collaborator Norman Horowitz 00:09:22.669 --> 00:09:25.230 officially gave this concept its famous name. 00:09:25.480 --> 00:09:27.980 The one -gene -one enzyme hypothesis. Right. 00:09:28.179 --> 00:09:30.539 And Beadle and Tatum eventually won the 1958 00:09:30.539 --> 00:09:32.940 Nobel Prize for this exact work. Very well deserved. 00:09:33.100 --> 00:09:35.019 Okay, here's where it gets really interesting. 00:09:35.179 --> 00:09:37.100 Look at the date of that initial paper, late 00:09:37.100 --> 00:09:39.840 1941. Right in the thick of it. The world is 00:09:39.840 --> 00:09:42.860 engulfed in World War II. This research did not 00:09:42.860 --> 00:09:46.299 just sit in an ivory tower. It found immediate, 00:09:46.639 --> 00:09:49.240 surprising real -world application. Yeah, this 00:09:49.240 --> 00:09:52.220 is one of the earliest examples of the military 00:09:52.220 --> 00:09:56.029 directly funding biological science. Beetle actually 00:09:56.029 --> 00:09:59.330 used these highly specific nutritional mold mutants 00:09:59.330 --> 00:10:02.090 to secure funding from the Rockefeller Foundation 00:10:02.090 --> 00:10:05.250 and an association of military ration manufacturers. 00:10:05.490 --> 00:10:07.929 Which sounds crazy, right? Mold mutants in military 00:10:07.929 --> 00:10:10.669 rations. It's wild. They use the mutated bread 00:10:10.669 --> 00:10:13.389 mold to physically test the nutrient content 00:10:13.389 --> 00:10:16.769 of foodstuffs for the troops. Wow. Yeah. So if 00:10:16.769 --> 00:10:18.710 they had a strain of mold that would only grow 00:10:18.710 --> 00:10:21.250 if vitamin B1 was present, they would expose 00:10:21.250 --> 00:10:24.009 it to a sample of a military ration. If the mold 00:10:24.009 --> 00:10:26.570 grew, they had undeniable proof that the ration 00:10:26.570 --> 00:10:28.870 contained enough vitamin B1 for the soldiers. 00:10:29.269 --> 00:10:31.629 It's an incredible practical application of what 00:10:31.629 --> 00:10:34.590 was essentially abstract genetic research. But 00:10:34.590 --> 00:10:37.129 if we connect this to the bigger picture, the 00:10:37.129 --> 00:10:39.470 impact on pure science was explosive. It changed 00:10:39.470 --> 00:10:41.909 everything. Remember how the consensus was that 00:10:41.909 --> 00:10:44.990 genes only controlled trivial things? This bread 00:10:44.990 --> 00:10:47.929 mold experiment completely shattered that paradigm. 00:10:48.190 --> 00:10:50.250 It demonstrated that genes have an absolutely 00:10:50.250 --> 00:10:54.009 essential role in basic biosynthesis. By 1945, 00:10:54.230 --> 00:10:56.870 they expanded their work to E. coli bracteria 00:10:56.870 --> 00:10:59.870 and proved that each step in a metabolic pathway 00:10:59.870 --> 00:11:02.870 is controlled by a single gene. They showed that 00:11:02.870 --> 00:11:05.450 genes are fundamentally instructional. This is 00:11:05.450 --> 00:11:07.909 the birth of molecular biology. The manual for 00:11:07.909 --> 00:11:10.649 life. Exactly. It provided the entire foundation 00:11:10.649 --> 00:11:13.730 for the concept of a genetic code. The realization 00:11:13.730 --> 00:11:16.549 that DNA is essentially an instruction manual 00:11:16.549 --> 00:11:19.690 for building proteins and enzymes. But as with 00:11:19.690 --> 00:11:22.250 all monumental breakthroughs in science, it immediately 00:11:22.250 --> 00:11:25.129 attracted monumental skepticism. Of course, it 00:11:25.129 --> 00:11:27.309 always does. The scientific community just wasn't 00:11:27.309 --> 00:11:29.570 completely sold that life could be boiled down 00:11:29.570 --> 00:11:31.970 to such a neat mathematical one -to -one ratio. 00:11:32.169 --> 00:11:34.169 Yeah, Max Delbruck, who was a massive figure 00:11:34.169 --> 00:11:36.370 in genetics at the time, was highly skeptical. 00:11:36.690 --> 00:11:38.970 He strongly doubted that only a single enzyme 00:11:38.970 --> 00:11:41.549 was involved at each step along these complex 00:11:41.549 --> 00:11:44.850 metabolic paths. pathways. And beyond just individual 00:11:44.850 --> 00:11:48.090 skepticism, there was a massive wave of scientific 00:11:48.090 --> 00:11:50.909 confusion happening around the same time involving 00:11:50.909 --> 00:11:55.389 the tobacco mosaic virus. Right, the TMV confusion. 00:11:55.450 --> 00:11:58.490 Yeah, the one gene one enzyme hypothesis strengthened 00:11:58.490 --> 00:12:01.350 the link between genes and enzymes so much that 00:12:01.350 --> 00:12:05.970 it caused a severe overcorrection. A lot of biochemists 00:12:05.970 --> 00:12:08.409 started to legitimately think that genes simply 00:12:08.409 --> 00:12:11.149 were enzymes. Which we have to remember the chronology 00:12:11.149 --> 00:12:13.850 here. This was before the double helix structure 00:12:13.850 --> 00:12:16.929 of DNA was discovered. They didn't fully understand 00:12:16.929 --> 00:12:19.669 the physical basis of heredity yet. Right. So 00:12:19.669 --> 00:12:21.769 researchers were studying this tobacco mosaic 00:12:21.769 --> 00:12:24.789 virus, which had heritable variations. When they 00:12:24.789 --> 00:12:26.730 crystallized the virus to study its structure, 00:12:27.129 --> 00:12:30.539 it looked like a pure, solid protein. So because 00:12:30.539 --> 00:12:32.379 they could crystallize it into a protein and 00:12:32.379 --> 00:12:35.179 because it carried genetic info, the logical 00:12:35.179 --> 00:12:37.539 leap they made was, ah, genetic material is made 00:12:37.539 --> 00:12:39.879 of proteins, genes are just enzymes. It is a 00:12:39.879 --> 00:12:42.139 perfectly logical conclusion based on the visual 00:12:42.139 --> 00:12:44.039 evidence they had, even though it was completely 00:12:44.039 --> 00:12:46.120 backward. Totally backward. But because of this 00:12:46.120 --> 00:12:49.120 confusion, Beadle's work was viewed by many as 00:12:49.120 --> 00:12:52.620 a vast oversimplification. In fact, at the famous 00:12:52.620 --> 00:12:56.120 Cold Spring Harbor Symposium in 1951, the prevailing 00:12:56.120 --> 00:12:58.759 view was deeply hostile to the one -to -one idea. 00:12:59.000 --> 00:13:01.379 Yeah, Beadle actually wrote a retrospective in 00:13:01.379 --> 00:13:05.379 1966 looking back at that 1951 symposium. He 00:13:05.379 --> 00:13:08.000 noted that the supporters of his hypothesis could 00:13:08.000 --> 00:13:10.059 be counted on the fingers of one hand with a 00:13:10.059 --> 00:13:12.340 couple of fingers left over. He was incredibly 00:13:12.340 --> 00:13:15.700 isolated, defending his own Nobel -winning concept. 00:13:15.820 --> 00:13:19.220 It wasn't until the early 1950s when biochemists 00:13:19.220 --> 00:13:22.419 finally proved that DNA nucleic acid, not protein, 00:13:22.740 --> 00:13:24.740 was the actual physical substance of the gene 00:13:24.740 --> 00:13:27.519 that Betel's hypothesis was universally embraced. 00:13:27.759 --> 00:13:29.720 But, you know, as Delbrick suspected years earlier, 00:13:30.039 --> 00:13:32.179 the pushback wasn't entirely wrong. The rule 00:13:32.179 --> 00:13:35.259 was an oversimplification. Right. The first major 00:13:35.259 --> 00:13:38.519 crack in the rule happened in 1957. This was 00:13:38.519 --> 00:13:40.580 thanks to a researcher named Vernon Ingram who 00:13:40.580 --> 00:13:42.799 was studying the genetics of sickle cell anemia. 00:13:43.059 --> 00:13:45.919 And his discoveries forced a major pivot. he 00:13:45.919 --> 00:13:48.379 shifted the paradigm from 1 -gene -1 enzyme to 00:13:48.379 --> 00:13:51.519 the 1 -gene -1 polypeptide hypothesis. Hold on. 00:13:51.519 --> 00:13:53.240 What is the meaningful difference here? Like, 00:13:53.240 --> 00:13:55.440 why did they have to change enzyme to polypeptide 00:13:55.440 --> 00:13:57.440 just because of a sickle cell mutation? Good 00:13:57.440 --> 00:14:00.720 question. So advancements in biochemical genetics 00:14:00.720 --> 00:14:04.299 allowed scientists to use techniques like electrophoresis 00:14:04.299 --> 00:14:07.019 and chromatography to look much closer at the 00:14:07.019 --> 00:14:09.419 physical structure of proteins. Basically using 00:14:09.419 --> 00:14:12.340 electricity and specialized paper to pull molecules 00:14:12.340 --> 00:14:14.620 apart by their size and charge, right? To see 00:14:14.620 --> 00:14:16.899 the building block. Exactly. And by pulling these 00:14:16.899 --> 00:14:19.500 proteins apart, Ingram and others discovered 00:14:19.500 --> 00:14:23.039 that enzymes are incredibly complex. Betel and 00:14:23.039 --> 00:14:25.639 Tatum originally thought an enzyme was a single 00:14:25.639 --> 00:14:29.000 monolithic block built by one gene. Like a single 00:14:29.000 --> 00:14:31.879 Lego brick. Right. But Ingram proved that many 00:14:31.879 --> 00:14:34.399 enzymes and proteins like the hemoglobin or blood 00:14:34.399 --> 00:14:37.759 are multimeric. Meaning they are made of multiple 00:14:37.759 --> 00:14:40.879 distinct puzzle pieces. Exactly. Human hemoglobin 00:14:40.879 --> 00:14:43.379 is actually made of four separate polypeptide 00:14:43.379 --> 00:14:46.639 chains. Two alpha chains and two beta tones all 00:14:46.639 --> 00:14:50.250 folded together. So it's like Voltron. Yes, exactly 00:14:50.250 --> 00:14:53.129 like Voltron. And Ingram showed that the genetic 00:14:53.129 --> 00:14:55.350 variation causing sickle cell disease wasn't 00:14:55.350 --> 00:14:58.009 changing the entire hemoglobin protein. It was 00:14:58.009 --> 00:15:00.110 just changing one piece. Right. The mutation 00:15:00.110 --> 00:15:02.690 was isolated to a difference in just one of those 00:15:02.690 --> 00:15:07.090 specific beta polypeptide chains. Ah, okay. So 00:15:07.090 --> 00:15:09.350 one gene doesn't manufacture a whole enzyme, 00:15:09.610 --> 00:15:12.470 one gene makes one polypeptide chain, and then 00:15:12.470 --> 00:15:14.769 multiple chains from entirely different genes 00:15:14.769 --> 00:15:18.070 assemble together to form the final enzyme. Exactly. 00:15:18.529 --> 00:15:21.789 The original rule was simply too broad. As the 00:15:21.789 --> 00:15:25.330 geneticist Roland H. Davis later noted, by 1958, 00:15:25.809 --> 00:15:28.830 the one -gene -one -enzyme concept was no longer 00:15:28.830 --> 00:15:31.730 a hypothesis to be resolutely defended. It just 00:15:31.730 --> 00:15:33.649 became the name of a research program. Right. 00:15:33.909 --> 00:15:36.350 A useful shorthand, but technically inaccurate. 00:15:36.639 --> 00:15:38.759 But of course biology wasn't done complicating 00:15:38.759 --> 00:15:41.259 things. As our tech kept improving into the late 00:15:41.259 --> 00:15:44.120 1970s, scientists discovered that the microstopic 00:15:44.120 --> 00:15:46.799 world is infinitely more chaotic than even Vernon 00:15:46.799 --> 00:15:50.000 Ingram realized. Oh, absolutely. The final shatter 00:15:50.000 --> 00:15:52.899 of the one -to -one ratio happened in 1977. With 00:15:52.899 --> 00:15:55.860 the discovery of the splicisum. Yes, by Philip 00:15:55.860 --> 00:15:58.500 Sharp and Richard J. Roberts. The splicisum is 00:15:58.500 --> 00:16:00.899 so fascinating to me because it completely breaks 00:16:00.899 --> 00:16:03.480 the updated one -gene -one polypeptide rule, 00:16:03.700 --> 00:16:06.639 too. It shatters it entirely. And to understand 00:16:06.639 --> 00:16:10.120 why, we have to look at how RNA works. When a 00:16:10.120 --> 00:16:13.120 gene is read, it produces a raw RNA transcript. 00:16:13.659 --> 00:16:15.820 But that raw transcript isn't ready to build 00:16:15.820 --> 00:16:18.460 a protein yet. It's got extra stuff in it. Exactly. 00:16:18.820 --> 00:16:21.519 It contains vital coding sections called exons 00:16:21.519 --> 00:16:24.840 and non -coding filler sections called introns. 00:16:25.559 --> 00:16:28.480 A spliceosome is a complex piece of cellular 00:16:28.480 --> 00:16:30.960 machinery that physically cuts out the filler 00:16:30.960 --> 00:16:33.759 introns and splices the coding exons together. 00:16:34.039 --> 00:16:36.740 Think of it like a single reel of raw film footage. 00:16:37.279 --> 00:16:39.679 The raw RNA is the unedited footage straight 00:16:39.679 --> 00:16:42.059 from the camera. The spliceosome is the film 00:16:42.059 --> 00:16:43.759 editor in the cutting room. That's a perfect 00:16:43.759 --> 00:16:46.169 analogy. Depending on what environmental signals 00:16:46.169 --> 00:16:48.549 the cell is receiving, that spliceous editor 00:16:48.549 --> 00:16:50.730 can cut the exact same reel of raw footage into 00:16:50.730 --> 00:16:53.450 a comedy, a drama, or an action movie. It can 00:16:53.450 --> 00:16:56.009 include some exons, skip others, and completely 00:16:56.009 --> 00:16:58.649 rearrange the final product. We call this alternative 00:16:58.649 --> 00:17:01.250 splicing, and it means that one single gene can 00:17:01.250 --> 00:17:03.529 result in multiple entirely different variations 00:17:03.529 --> 00:17:05.650 of a polypeptide. So the relationship between 00:17:05.650 --> 00:17:07.990 genes and proteins is not a simple static one 00:17:07.990 --> 00:17:10.789 -to -one ratio at all. Not even close. It is 00:17:10.789 --> 00:17:15.559 a highly dynamic, reactive, modular system. Before 00:17:15.559 --> 00:17:17.940 we wrap up the biological mechanics, there is 00:17:17.940 --> 00:17:20.500 a very juicy piece of historical drama in the 00:17:20.500 --> 00:17:22.400 sources that we absolutely have to talk about. 00:17:22.660 --> 00:17:25.599 Oh, the mo was controversy. Yes. Whenever there's 00:17:25.599 --> 00:17:28.079 a monumental scientific breakthrough, there is 00:17:28.079 --> 00:17:30.680 almost always a bitter fight over who really 00:17:30.680 --> 00:17:33.630 got there first. It's a tale as old as time in 00:17:33.630 --> 00:17:37.210 science. So historian Jan Sapp did a deep dive 00:17:37.210 --> 00:17:40.869 into the career of Franz Mewis, a German geneticist. 00:17:41.109 --> 00:17:43.609 Some leading geneticists fiercely argued that 00:17:43.609 --> 00:17:46.089 Mois actually generated the exact same results 00:17:46.089 --> 00:17:48.529 as Beadle and Tatum, but he did it years earlier 00:17:48.529 --> 00:17:51.450 in the 1930s. Working on clematomonas algae. 00:17:51.609 --> 00:17:54.230 Right. He published extensive data showing different 00:17:54.230 --> 00:17:56.509 genes were responsible for different enzymatic 00:17:56.509 --> 00:17:58.690 reactions controlling the algae's reproduction. 00:17:59.009 --> 00:18:01.359 Yet Mois does not share the Nobel Prize. He does 00:18:01.359 --> 00:18:04.579 not, because as SAP's research details, Moses' 00:18:04.720 --> 00:18:07.480 peers aggressively challenged his results. They 00:18:07.480 --> 00:18:09.579 looked at his published data and mathematically 00:18:09.579 --> 00:18:12.000 dismantled it. They said his numbers were statistically 00:18:12.000 --> 00:18:15.019 too good to be true. Which is such a burn in 00:18:15.019 --> 00:18:17.940 the science world. It really is. When you run 00:18:17.940 --> 00:18:20.740 a biological experiment hundreds of times, the 00:18:20.740 --> 00:18:23.839 natural world guarantees that the numbers should 00:18:23.839 --> 00:18:25.980 be a little messy. There should be statistical 00:18:25.980 --> 00:18:29.059 variance. But Moses' data was mathematically 00:18:29.059 --> 00:18:32.920 flawless. Exactly. His peers looked at the statistical 00:18:32.920 --> 00:18:35.400 probability of getting those exact, perfectly 00:18:35.400 --> 00:18:37.819 clean numbers organically and realized it was 00:18:37.819 --> 00:18:40.099 practically impossible. And the final nail in 00:18:40.099 --> 00:18:42.819 the coffin. His results could not be replicated 00:18:42.819 --> 00:18:45.559 by any other independent laboratory. This raises 00:18:45.559 --> 00:18:47.460 an important question about the very nature of 00:18:47.460 --> 00:18:49.680 scientific discovery, you know? Yeah. Like, what 00:18:49.680 --> 00:18:52.940 is truth in science? Yeah. Was Mois a visionary 00:18:52.940 --> 00:18:56.039 who just lacked the resources and PR to get his 00:18:56.039 --> 00:18:59.180 genuinely forward -thinking ideas accepted? Or 00:18:59.180 --> 00:19:02.099 does science correctly rely on rigorous, unforgiving 00:19:02.099 --> 00:19:05.039 replicability to validate data that looks too 00:19:05.039 --> 00:19:07.319 good to be true? It's a tough balance, but in 00:19:07.319 --> 00:19:09.759 the scientific method, being conceptually right 00:19:09.759 --> 00:19:11.759 isn't enough. You have to be able to prove it 00:19:11.759 --> 00:19:14.059 in a way that others can independently verify. 00:19:14.400 --> 00:19:16.359 And Betel and Tatum could do that with their 00:19:16.359 --> 00:19:19.519 bread mold. The Oxotroph experiment was undeniably 00:19:19.519 --> 00:19:22.079 clear. You could hand a Petri dish to a skeptic 00:19:22.079 --> 00:19:24.299 in another country, and they could literally 00:19:24.299 --> 00:19:27.720 see the mold die on a minimal medium and thrive 00:19:27.720 --> 00:19:30.460 on a complete medium with their own eyes. Right. 00:19:30.700 --> 00:19:33.599 And even though Betel and Tatum's strict mathematical 00:19:33.599 --> 00:19:36.460 one -to -one ratio was eventually proven wrong 00:19:36.460 --> 00:19:40.059 by discoveries like the Splicy Sum, their informational 00:19:40.059 --> 00:19:42.880 approach to genes laid the essential groundwork 00:19:42.880 --> 00:19:45.480 for solving the entire genetic code. It is an 00:19:45.480 --> 00:19:48.220 amazing journey. I mean, from staring at the 00:19:48.220 --> 00:19:51.880 tedious red pigments of fruit fly eyes, to deliberately 00:19:51.880 --> 00:19:55.279 blasting bread mold with radiation, to testing 00:19:55.279 --> 00:19:57.779 military rations in World War II, all the way 00:19:57.779 --> 00:20:00.319 to uncovering the microscopic editing floor of 00:20:00.319 --> 00:20:02.940 the Splay CSM. It is a phenomenal arc of discovery 00:20:02.940 --> 00:20:05.410 that spans the entire 20th century. We always 00:20:05.410 --> 00:20:07.289 like to bring this wealth of information back 00:20:07.289 --> 00:20:09.289 to you, the listener. You've heard the history, 00:20:09.329 --> 00:20:12.430 you've unpacked the biochemistry. So what does 00:20:12.430 --> 00:20:14.369 this all mean for you? I think the ultimate value 00:20:14.369 --> 00:20:16.970 of this deep dive is understanding the vital 00:20:16.970 --> 00:20:20.549 role of being wrong in a productive way. I love 00:20:20.549 --> 00:20:23.569 that. In the pursuit of knowledge, an imperfect 00:20:23.569 --> 00:20:28.230 or oversimplified model like one gene equals 00:20:28.230 --> 00:20:31.410 one enzyme is not a failure of science. It is 00:20:31.410 --> 00:20:34.049 an absolutely necessary stepping stone. You have 00:20:34.049 --> 00:20:37.490 to start somewhere. Exactly. Science often requires 00:20:37.490 --> 00:20:41.170 us to build a simple, slightly incorrect model 00:20:41.170 --> 00:20:44.130 just to give us the vocabulary and the framework 00:20:44.130 --> 00:20:46.730 to eventually discover the much more complex 00:20:46.730 --> 00:20:51.400 truth. Without Beadle and Tatum's brilliant oversimplification, 00:20:52.019 --> 00:20:54.519 the highly nuanced reality of molecular genetics 00:20:54.519 --> 00:20:57.079 could never have been reached. You have to build 00:20:57.079 --> 00:20:59.039 the ladder before you can climb it. Even if you 00:20:59.039 --> 00:21:00.599 eventually realize the ladder is made of wood 00:21:00.599 --> 00:21:02.599 and you actually need a steel elevator, you still 00:21:02.599 --> 00:21:04.180 needed that ladder to get off the ground. That 00:21:04.180 --> 00:21:06.039 is a perfect way to frame it. Which leaves me 00:21:06.039 --> 00:21:08.079 with a final thought for you to mull over today. 00:21:08.440 --> 00:21:10.160 Think about how our understanding of genetics 00:21:10.160 --> 00:21:12.960 started. It was a mysterious black box in the 00:21:12.960 --> 00:21:15.779 cytoplasm. Then it evolved into a neat, clean, 00:21:15.940 --> 00:21:18.140 one -to -one blueprint, and now we know it's 00:21:18.140 --> 00:21:21.019 this incredibly messy, dynamic, ever -changing 00:21:21.019 --> 00:21:23.619 world of spliceosomes. It's constantly evolving. 00:21:23.900 --> 00:21:27.609 It makes you wonder. What universally accepted 00:21:27.609 --> 00:21:30.549 simple truths in today's cutting edge sciences, 00:21:31.069 --> 00:21:33.410 whether that's the mechanics of artificial intelligence 00:21:33.410 --> 00:21:36.630 or quantum physics or dark matter, what clean, 00:21:36.809 --> 00:21:38.769 simple models are we clinging to right now that 00:21:38.769 --> 00:21:41.490 are just temporary stepping stones waiting to 00:21:41.490 --> 00:21:43.970 be beautifully shattered by tomorrow's discoveries? 00:21:44.309 --> 00:21:46.170 It's a thrilling thing to think about. There 00:21:46.170 --> 00:21:49.250 is always more to learn. There really is. Thank 00:21:49.250 --> 00:21:51.410 you for joining us on this deep dive. Keep asking 00:21:51.410 --> 00:21:53.430 questions, keep challenging the simple truth, 00:21:53.430 --> 00:21:54.750 and we will see you next time.