Ep 4 - The Genetic Code - Part 1

How did life go from random chaos to organized machinery? Three-letter words. In this episode, we meet the RNA family - Mary, Rick, and Tina - and discover how they invented the genetic code. The same code you, me, E. coli, and blue whales all still use today.

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Jackie 0:04

Hello, i'm your host, Jackie Mullens, and welcome to From Cells to Us. How the podcast where we figure out how life went from a single cell to complex creatures like us. Last episode, we watched RNA accidentally create its own boss, DNA, showed up, same basic blueprint, one oxygen atom removed, and suddenly. RNA had a filing cabinet that actually worked. Stable double helix, built in backup system, the Queen of England, just sitting there all high and mighty looking important, holding all the hereditary information. But RNA, yeah, it's still the British government still doing all the work. So we've got our team assembled. DNA storing information, RNA, reading it peptides, helping with chemistry and a fatty acid membrane holding this whole circus together like a bouncer who's really bad at his job because things are still getting in, but it's not just the membrane who has some gaps here. It was chaos in that proto cell, RNA would read DNA. Grab some amino acids, stick 'em together, but there was no system, no organization. It's like if you walked into Subway and instead of being like Turkey, lettuce, tomato on wheat, you just said meat, bread stuff, you know and hoped for the best. Sometimes you'd get a sandwich. Sometimes you'd get a pile of ingredients thrown in your face because that subway worker is like, ask, screw you buddy. Life needed a menu, a way to say this sequence. Means this amino acid every time. Not, Hey, give me stuff life needed a language. Today we're talking about the genetic code, the three letter words that tell RNA exactly which amino acid to grab next. That tells the umbrella people, which potatohead to grab. And this code is so universal, so locked in that bacteria to blue whales to you are all speaking the exact same molecular language. Let's get into it. Okay, so let's picture our proto cell situation here. DNA has sequences, you know, long strings of A-A-T-G-C. That's the information. Great. RNA reads those sequences. And then what? How does RNA carry out what DNA is saying to do? Because we figured out how to keep instructions, right? We transferred information from tissue paper, RNA to a fireproof safe of DNA. But how do those instructions get carried out? DNA cannot perform its own chemistry, like RNA. So what's next? Well, in the early days, like we just talked about in episode three, RNA would fold up. Maybe grab an amino acid that happened to fit in one of its pockets, stick it to another amino acid, and boom, you know, a peptide, but which amino acid, oh, whichever was nearby, whichever fit. It was like grabbing three Scrabble tiles out of a bag blindfolded, and hoping you spelled something. You know, maybe you'd get cat, but most of the time you'd get Zig or something like that and look, this worked okay for a while. Random peptides would form, some would be useful. Most would be garbage. Natural selection would sort it out. Classic evolution. Throw stuff at the wall and see what sticks. But here's the problem. You can't build anything complex with randomness. You just can't. Life needed precision. Life needed to go from cavemen, grunting, and pointing to Babylonians in the first civilization that could read and write. That's a big jump. And this big jump started with what else? But RNA, the champion of change. The versatile veteran, the colossus of Catalyst. The colossus of Catalyst. Shut up Tommy. It's your very own RNA. So RNA confused me in college. I was like, why? Why? Why are there so many? Why don't we name them something else? Everyone knows if you don't capitalize the first letter in front of those three capital letters. We're just going to ignore it. Like are we talking about R-N-A-R-R-N-A-T-R-N-A? Mr. A. They all look the same when you're speed reading through a textbook at 2:00 AM Also because they sound so similar I'm personifying them here. You don't want to hear me say T-R-N-A-R-R-N-A-M-R-N-A over and over. That's boring. And that's lame. And I'm not like a regular mom. I'm a cool mom. So we're giving these three RNAs names. Pay attention. 'cause this is going to be throughout, it's way easier for you and me. TRNA transfer, RNA is going to be Tina, RRNA ribosomal. RNA is going to be Rick and MRNA messenger, rNA is going to be Mary. So. I have all the RNAs down pat now, and I have to say I'm very glad that I do because I am truly RNAs biggest fan. It's literally the genie from Aladdin. The cell is like, Hey, we need you to do chemistry. Uh, we need you to give up storing information and make another molecule that can do it better. Mm. But also we need you to be the runner between DNA and proteins. And RNA is all like, poof, what do you need? Poof. What do you need? Poof, what do you need? But this poor sucker is never being freed. And I just wanna let you know, I'm gonna make an RNA fan out of you too. Listen, al, make a fan. Out of you. We are heavy on Disney's nineties right now, and I am not hating it. so for the next few minutes, i'll be discussing how these three RNA strands specialized, how they learned and evolved to read DNA's instructions to make proteins how RNA became the runner between DNA and proteins like what they're doing inside of you right now. Now because they evolved from how they were previously. I'll have some episode two recall. If you don't remember, don't worry about it. I'll give a brief, remember this section just to jog your memory, but again, don't stress. Remember, our main issue here is how RNA figured out how to take DNA code and make proteins that could work and that took three kinds of specialization. We'll need an RNA to pick the correct amino acid every time. We'll need a place where we can attach the correct amino acids together in the correct order. And of course, we need the directions from DNA. First up is TRNA transfer, RNA, our Tina. So remember from episode two when I said that sometimes when RNA folded into certain shapes, it would accidentally grab an amino acid nearby, and that sometimes it wasn't completely random. Like if there were a few amino acids milling around, one might have a higher probability of being grabbed. Just because of how the RNA folded, like maybe when it folded, it had a negative charge in that pocket and that specific amino acid had a positive charge. So that type of fold grabbed that specific amino acid more reliably and so on and so forth with. Different folds being better at grabbing specific amino acids until natural selection kept the RNA sequence that reliably grabbed one specific amino acid every time. So basically instead of panicked umbrella people just trying not to get wet and pairing with whoever. You remember those nucleotide hussies? Well now they had standards, a specific fold for a specific potato head specific is very hard to say over and over anyway, these umbrella people had tired of their hedonistic ways. They'd settle down. Found their one true amino acid. RNA was going steady. So natural selection kept the folds that successfully grabbed useful amino acids, and over millions of years, you ended up with RNA molecules that were really good at grabbing one specific amino acid every time those specialized RNA molecules. TRNA, we have Tina, and Tina is called the delivery truck of the genetic code. If you need a visual on what Tina looks like, picture, a claw machine. You know the claw. The claw decides who will stay and who will go. Tina reaches in, grabs one specific amino acid and delivers it. That's Tina's job. So one type of RNA down TRNA or Tina now two to go. So right now. I just wanted to say this isn't a full fledged Tina, which we have in our cells today. This is a proto Tina. It's kinda like an intern. So we've got our proto tinana, the molecular delivery trucks. Tina grabs a specific amino acid and brings them and brings them, well shoot. Where are they bringing these specific amino acids? It took so much effort and selecting for, but now you have nowhere to go. You can't just have trucks driving around Aimlessly. We need a factory, a workstation, an assembly line. Enter RRNA, ribosomal, RNA. Our second type. Here's Rick. Now Ribozymes. Let's do a quick flashback here. These are those folded, RNA molecules that could act as enzymes, making reactions happen faster. Remember not waiting for magnets to snap together on a table, but pushing them together. Well, some rib enzymes got really good at one specific job. Linking amino acids together or making the potato heads hold hands. And these Ricks weren't only grabbing random amino acids anymore. They were positioning them perfectly, holding them steady, snapping them together into chains, peptide bond after peptide bond. It's like forming a friendship bracelet where you have to glue each bead to the next one. And Rick was doing all of this. And these Ricks, well, they started getting kind of cliquey. They were clustering together. A bunch of cool guy Ricks just hanging out. All really good at making potato heads, hold hands and word got around. This became the spot to be the hot spot where Tina Trucks could drop off their single unattached amino acids to be linked up with a lovely new chain of friends. Rick was basically a matchmaker for lonely potato heads, but remember, RNA is still fragile. That hasn't changed. What has changed is remember when a rib zyme would just keep linking amino acids, just keep having potato heads grab hands, and the chain got so long it popped out of the nook, RNA provided, and instead of just waving in the wind, these long peptides wanted to be useful. They wrapped themselves around the other parts. Of the RNA strand like wrapping a sprained ankle, keeping it steady, keeping it from falling apart like the other RNA strands. Well, Rick liked that and so did natural selection, so they kept it. And here's the part that blows my mind. This accidental extra long peptide chain that just happened to wrap around the RNA. Well, now it's essential. It's like if you were building something with wood and you were pushing the pieces together, but they're not really meant to stay like that. So you drill a bunch of nails in and it holds, you know, hopefully for a while because you need that shape for your end product. These peptides formed around Rick, lacking him into the correct shape and we know how important the right fold is. Right? Fold defines function. If a piece of paper folds into a cup, its function is to hold water. Well, these peptides were locking Rick into one job, linking amino acids together, pigeonholing him, and what an important job to be pigeonholed in. Tina needed somewhere to bring her amino acids. And now Rick was that place, a rigid structure held in shape by peptides, but still keeping that special fold that could catalyze reactions. Still able to snap those amino acids together into chains without fear of, you know, dissolving into a puddle. And this new combo. Proteins plus rib zyme. It has a special name. The ribosome, not the rib zyme, the ribosome. I know, I know. Well, proto ribosome at this point, the ribosomes in your cells today. Yes. We literally have these in our cells Right now, they're more complex, but they still have the same ancient RNA at the core, billions of years later, still doing the same job, which is pretty cool. And you can kind of think. The ribosome as like Darth Vader. He has these awesome powers he can use, but he's fragile, broken, wouldn't survive long without help. Then wrap him up in that life support armor in obsidian black, obviously, and suddenly he's running the death star. Well, that's Rick, the RRNA inside is fragile. It would fall apart on its own, but rapid in proteins and now it's stable. Now it's powerful. Now it's a ribosome. So to be clear, a ribosome is RRNA and proteins. So the ribosome is just rib zyme 2.0. You know, a catalytic RNA just got an upgrade to. A ribosome same RNA core now just with protein support Making it the go-to spot for all the single amino acids that just wanna mingle, that just wants someone to bond with. So let's think about how far we've come. We went from a scramble of clueless, RNA strands, randomly grabbing amino acids out of the molecular junk drawer. Thanks leaky membranes to mashing them together if they happen to be close enough. To now two specialized RNAs with two specialized jobs. Tina grabs a specific amino acid and brings it to the party. Rick is the party linking those amino acids into chains. Peptide bond after peptide bond, eventually proteins. As a reminder, I know I'm interchanging peptides and proteins. Uh, here's the deal with that. A short chain of amino acids is a peptide, a longer chain that folds into a functional shape that's a protein. So it's about length and whether it's doing a job for now, just know they're both chains of amino acids. Peptides are the baby version. Proteins are all grown up. So right now we have TRNA, Tina carrying specific amino acids and an upgraded rib zyme ribosome, complete with RRNA, Rick and proteins linking amino acids together. Two down, one to go. We have our last RNA type, MRNA messenger, our Mary. So here's where it gets a little tricky, because in early proto cells, there wasn't really a separate Mary yet I had a hard time deciding when to introduce you to Mary, and ultimately decided now earlier, even though Rick and Tina weren't really friends with Mary yet. Because Mary's job was to take the information DNA had and bring it to the party, bring it to Rick, but at this time, at this prototype, that wasn't really happening. So if I had to make an analogy of these three RNAs, I'd say Tina was the dd, the designated driver. She made sure she picked up the right people, the right drunk amino acids. Rick is the owner of the party just waving people in. He trusts Tina, the DD, to have brought the right people. But Mary has the party list, the special order the guests need to arrive in. However, Rick, at this point, he's a freshman. You know, a noob, an overconfident fool. He ignores Mary and just starts attaching the amino acids. Tina drops off in whatever order the drunk amino acids form a conga line, and, you know, parade themselves through the house, out the back door, holding shoulders in a firm peptide bond to be free onto the world. Now, Rick doesn't listen to Mary, so that conga line of amino acids may or may not be useful. So why do we need Mary? Well, DNA has the instructions great, but DNA doesn't move. It's like all those happy couples of at and GC have paired up and now they don't wanna go out anymore. They're gonna stay right where they are, cuddled up on the couch watching reruns in the middle of the cell. They're happy, they're not going anywhere. So how does Mary get this information from DNA? Like, does it beat it out of them? Let out some pent up frustration at having their job taken. Listen, I'm gonna give you to the count of 10 to get you ugly, yellow, no good keys are off my property. I mean a little bit, but physics is doing the beating up. Just like last episode. Physics shakes the DNA double helix open, so it's got two open strands, basically two magnetic strips just waiting for the opposite piece to click into place free RNA nucleotides come in a UCG to make a small copy of the DNA strand when the copy is completed. Now we have our Mary, so. Mary isn't floating around pre-made, just waiting for its chance. Mary is a copy of DNA's instruction. It can't be a strand until it has an order and it doesn't have an order until it's built off of DNA's template. Just like how individual Lego bricks aren't really anything great until you read the instructions on how to make Ron Wesley's flying forward Anglia, which my son just got for Christmas and I am really excited to build with him. Now you also might be a little confused, like yes, you think to yourself, we did just talk about this last episode, and that was about DNA copying itself, not Mary. What's the difference? Well, the difference is if it's DNA nucleotides forming on the unzipped DN. Or RNA nucleotides forming on the unzipped DNA. It's like an empty parking lot. Same spaces either way. But if a fleet of cars show up, you get a lot full of cars. And if a fleet of trucks show up, you get a lot full of trucks. DNA nucleotides show up. DNA strand, RNA nucleotides show up. You get a Mary. We are unsure how early Protocells signaled whether it was to make a DNA strand or an Mr. NA strand, a Mary. Today there are precise instructions, but back then, you know, maybe it had to do with how far the DNA unzipped or what type of physics caused it to unzip. Or maybe it was just a free for all. Whoever got there first, got there first, like that cheese wheel race downhill. Things are just flying around. No one really knows what's going on, but they're all moving. Also, I know I haven't really mentioned the different nucleotides for DNA and RNA. It is important, but we'll tackle it for next episode. For now, just know that RNA uses a U where DNA uses a t. All right. That is a lot of information. Let's, uh, do a checkpoint. Let's go through the RNA family. We have TRNA, which is our tna, and it carries one specific amino acid. It's the delivery truck, the DD driver to the party. Then we have our RNA our Rick. It does the chemistry makes peptide bonds between the amino acids that Tina brings over. He's inside the party house making the correct guests hold each other's hands. MRNA our Mary. Mary carries the genetic message that was copied from the big dog himself, DNA. Now, Mary wants to be included in the party. It knows it has important information, but is being ignored also, I'm doing more personification here. Mary never actually shows up at Rick's party. More than likely, Mary is just drifting around the proto cell with this wealth of information not being fully utilized yet. So all three are RNA. All three descended from those original RNA molecules, the ones that did everything that could grab things, catalyze reaction, store information. They just each picked a specialty. And all three are about to come together and do something incredible. So that was fun. Are you a fan of RNA now or are you too annoyed at how many there are. Either way. You can't deny they are impressive. So we have the players, but how does the code work? You understand that DNA gets shaken open, then by luck, speed or physics free. RNA nucleotides attach themselves to the open DNA strand forming a Mary strand. Mary has DNA's information, but Rick has not seen it. Tina is picking up. Specific amino acids and bringing them to Rick. Rick is combining them into a peptide all willy-nilly. Meanwhile, Mary turns away dramatically as its special list is dropped, wafting in the wind and somehow lands in a puddle and the conga line full of amino acids form a maybe useful, maybe not. Peptide chain or protein. So at this point in the proto cell life, things are getting more organized, but we're not quite there. As you see step by step, we get closer. Now we are grabbing the same amino acid every time, but we're not doing it in the right order. Now we have a specialized RNA that binds amino acids together, even if the nooks aren't right next to each other, but he has no clue what he's making. We need to get Mary involved. How does that happen? Well, I won't lie to you fine folks. We simply don't really know. This is one of the big mysteries on how life began. We know what the system looks like now, but the exact steps of how Mary went from ignored list in a puddle to instructions everyone follows, well, that's still fuzzy. Here's what we do know. Somehow a connection formed between Mary and Rick, meaning Rick started listening to Mary and then started bringing over Tina's in the right order. And that connection came down to three little letters, to the universal code, to the language Every cell alive speaks today. So. We know it happened eventually, though. Unsure how, but right now we're at the part where Mary is getting noticed and not only noticed, it's the big man on campus. It's like when Tyler Posey went from second string lacrosse player to absolute starting stud. Thanks to those sweet werewolf jeans. But Mary doesn't have werewolf jeans. It has a special sequence of letters, which I would argue is better 'cause there are no worries about the full moon. See these very special letters? Well, they dictate which amino acid Tina needs to bring over. Some of you might be ahead of me here, like, Hey, how can four letters dictate which of the 20 amino acids to bring over? How do you map RNA? Letters to amino acids? Early life tried a bunch of options per the use, but here's what it's settled on. Three letters is equal to one amino acid. Those three letter chunks are called coons. Say it with me Coons. That's from Brother Bear. I'm not being condescending, although I think Coda was. So you might be thinking, why three letters? Why not two? Why not four? That's a great question. Let's do some math. I know it'll, it'll be quick. So what if we just had two letter codons? RNA has four bases. If codons were two letters long, four times four. 16 possible codons life uses. 22 codons wouldn't be enough. Well, how about four letters long? That would equal 256 possible codons. That's way more than you need. That's wasteful. That's like 10 buns and eight hot dogs. You should probably remove the superfluous buns. But if codons are three letters long. Four times four times four. That is 64 possible codons. That's perfect. That's enough to cover all 20 amino acids with some extras left over for redundancy, which actually helps. We'll get into that in episode five. Three letters is the goldilock zone. Not too few, not too many, just right, and that's what life picked. Three letter words, the genetic code. So let's do an example. Let's do code a UG. That is a code on that means grab methionine. When Mary shows up at the party with its list, Rick reads it and calls for Tina the DD, to bring methionine to the party. Now, each of the 20 amino acids has a specific three letter code on. But because there are 64 options, some have more than just that one. For example, if Mary brings over GGU or GGC, or GGA, or G. GG, Rick will read it and ask Tina to bring glycine. Glycine has four codons. Four words that mean glycine. There's only one for methionine, a UG, and that's important because that's our start here codon. When Rick sees a UG, it knows. This is where we begin building an important peptide chain. One that will eventually fold into a working protein. It's like the capital letter at the beginning of a sentence. So Rick reads the code, a UG, it calls for and grabs the start amino from Tina. Then it'll read the next three letter code from Mary's List and keep calling Tina over with the corresponding amino acid. The amino acids keep coming and Rick. Bonds them together. Now sending out a protein with a much higher probability of working. This is now Ford's assembly line. Miniaturized microscopically, miniaturized. So does this chain just keep forming? More and more? Amino acids get attached to the chain until the cell explodes. Much like when I never say when. When the waiter starts grating Parmesan cheese onto my pasta, the whole restaurant explodes. There are no survivors. No kidding. Obviously the peptide doesn't just keep getting built on one strand. That'd be crazy. You wouldn't be able to do anything with it. Rick stops calling Tina over when it hits the stop codon you a, a, a or two others. When that comes up on Mary's list, that's when they tie up the knot and send that peptide on its way. And also the waiter always just stops on their own, which is kind of annoying. Like why even tell me to say anything? Maybe I should start speaking in code on just yell UAA when I want something to stop. Or I should tell my kids to start talking to each other that way. Well, Jane Joe did say UAA and that is the universal code. Maybe you should listen to it too. Oh, don't you. A UG with me, young lady. Alright, so there you have it. That's the universal code, and it's not like. A start coat on is different for you or me or e coli or that mold that was growing on the water cup in the beer pong in that gross garage. How we all survived. I don't know. The start coat on and all codons are the same for every living thing. And I want that to really sink in because what an amazing thing that is. Take a cell from your body, a cell off a slug or an oak tree, and inside the instructions are the exact same. The cell is starting peptide chains at a UG and stopping at UAA. And because all living things have it, that means it evolved once, somewhere around 3.5 to 4 billion years ago. This system locked in and everything alive today inherited it and kept it. So let's do a quick recap because that's a lot of good information there. So what was the problem? RNA was still kind of winging it. There were grabbing specific amino acids. But putting them together in a random way, making unknown peptides sometimes useful, sometimes garbage. You can't build anything complex like that. The solution, three letter words made of nucleotides, A UGC, that each specify one amino acid four times. Four times 4 64 combinations. That's plenty. For our 20 amino acids, a UG our start here, and grab methionine. The capital letter at the beginning of a sentence, UA, a, and two others is stop, tie it off. Send that peptide on its way. The code is universal. You, me, e coli, slugs, oak trees, beer pong, mold, all using the same dictionary, the same start, the same stop, the same everything. That means it evolved once about 3.5 to 4 billion years ago, and nearly every living thing inherited it. We went from blindly grabbing Scrabble tiles out of a bag to a 64 word glossary that tells you exactly what to do. That is not a bad transition. All right, so now let's watch this whole system in action. Here's how the letters or coons changed the process. Now imagine Rick. He's throwing a party again. He's a senior, or you know what? Better yet, he's an adult out of college. The kegs and solo cups are replaced by fine wine IPAs and uh, glasses with charms on them. Rick is wiser. More learned. He waits for Mary to show up this time because now order matters. He reads the guest list. Mary presents three letters at a time. He uses each code on to call for the right Tina, first up a UG, the start signal. The Tinas or DDS show up in proper order, each dropping off their specific amino acid passenger. Rick connects each amino acid like before, but this time following Mary's list, the Congo line keeps forming until Rick reaches UAA, the stop signal, and then no, Tina is called the peptide. Congo line is sent out the back door this time, most likely working, most likely what the sequence wanted. And for early life, that difference was everything. Okay, so with real names. This time just for a check-in, so RRNA is just reading the Mr RNA, like a script calling for the right TRNA each time and stringing amino acids together in the exact order. The Mr. RNA specifies, that's translation, reading the genetic code and turning it into a protein. Also, probably why you realized I changed the names a little. Just that one sentence was a little brutal. Now let's be real. Early translation was rough. The proto Tinas wouldn't always show up on time. We're probably out the night before Classic Tina. Sometimes the wrong Tina would arrive. And sometimes Rick would skip a letter or read the wrong code on the whole system was like a middle school play. Everyone's trying their best, but there are missed cues, forgotten lines, and at least one kid who is clearly winging it, or one kid who is a playing card soldier from Alice in Wonderland and only has one line and it's written for them on a scroll, and they open the scroll upside down and run off the stage instead of saying the line, just as a random example. But here's the thing. Early earth's motto, it was good enough, even with errors, the party house ribosome could turn out peptides that were mostly correct and mostly correct. Was infinitely better than completely random? Natural selection took it from there, protocells with better translation systems, fewer errors, faster assembly survived better. They out competed the sloppier cells and after millions of years, the system got refined. The party house Rick was in, it got bigger, more complex, more accurate. The Tinas got better at listening to the Rix and grabbing the right amino acid. But the core was always there. Three letter codons, Mary to Rick and Tina with the delivery. The code was born. So let's do a quick recap. MRNA Mary carries the genetic message. A sequence of codons from D-N-A-T-R-N-A TTA brings specific amino acids. Each TNA matches one codon. Our RNA Rick reads Mary's list three letters at a time. Each coon calls for a specific Tina. Each Tina delivers a specific amino acid. The RX link them together into a protein chain. That's the genetic code in action. DNA stores it. Mr. NA carries it. TRNA and RRNA translate it into a protein. That's the genetic code in action. Information becomes reality. So why does this matter? Why is the genetic code such a big deal? Well, because now for the first time, life could build the same protein over and over again before the code RNA grabs random amino acids makes random peptides hopes for the best. Fingers crossed, you know, after the code DNA says, make this exact protein, Mary copies the message. Tina delivers the ingredients. Rick assembles them. In the correct order. Same protein every single time, reproducibility. And once you have reproducibility, you can build complexity. You can make proteins with hundreds of amino acids in a specific sequence. You can make enzymes that do very precise chemistry. You can make structural proteins that build cell walls or transport proteins that move molecules around, or regulatory proteins that turn genes on or off. Uh, it's almost endless. You can build systems, networks of proteins working together, the genetic. Code turned life from random chaos that occasionally works into organized machinery that works reliably. It's the difference between a pile of car parts and the actual car. However, there's always a, however, the code isn't optimized yet at the time we're talking about right now. It's not standardized. Different proto cells might be using slightly different versions of the code. Maybe a UG means one thing in one cell, but something else in another. It's like traveling to another country where they speak a different language. Sure, you can communicate point at things, make gestures, hope for the best, but it's slow and sloppy. You order coffee, you get a beer, it's 10:00 AM but honestly, it'd be harder to explain the mistake than just to crack it open. As always, I'm talking about a friend. That's what early life was like. Everyone kind of speaking, but not in the same language, and the code is still sloppy. Errors are everywhere. There's no quality control. Life needs this code to become universal, locked in the same, across life. And why? Why do we need that? Well, because if every organism is speaking a slightly different molecular language, they can't share genes, they can't swap useful innovations. They can't evolve together. They're isolated. But if everyone speaks the same language, now you can trade. Now you can share. Now evolution kicks it into high gear. So how did this messy error prone code become the universal language of all life on earth? Well, that's a story for episode five. Let's zoom out and see what we've covered. It was a good one. RNA didn't just sit back. When DNA took over storage, it specialized, it became three different types of worker. TRNA, Tina delivery trucks carrying the amino acid. RRNA. Rick was living inside the ribosome, Lincoln Amino acids together. MRNA Mary was the messenger carrying the instructions from DNA. And together they invented a language, three letter words called coons, each one meaning a specific amino acid. The party house ribosome with Rick. Inside reeds marries list three letters at a time. Calls for the matching Tina and assembles amino acids into proteins. That's translation. That's the genetic code. It was messy at first. Error prone, inconsistent, but it worked and natural selection, refined it and proved. Standardized it, but we're not done yet because this code, this three letter language, is about to become universal. Now you might be thinking, oh wait, you already told me it was universal, and yeah, I did. Spoiler alert, I suppose. But here's the thing. I told you where it ends up, not how it got there. Right now in the proto world, different proto cells might be running slightly different versions of the code. It's not locked in yet. It still has to prove itself. It still has to outcompete every other version until one wins and one will win. One version of the code will spread to every corner of the earth. Every living thing will speak it. Every bacterium. Every plant, every animal, every cell in your body, and once it's locked in, it will stay locked in for 3.5 billion years. Now that's what I call a winner. I. Next time on from cells to us, how the genetic code gets refined. Life discovers error correction, the central dogma is established. And Luca, now I know I was Disney heavy this episode, but no, not Luca, the fish boy, Luca, the last universal common ancestor emerges. And all the pieces finally start working together. I'm excited also. Four quick notes for the end here. One, I always thought it was pigeon holding, not pigeon holding. I literally thought they just meant that pigeons had really strong grips. So if anyone else thought that. It's not two. I totally stole that Parmesan cheese joke from a meme. Just so you all know, three, when I say all living things had this code, it is 99.9% true. There are a few very rare deviations like mitochondria They still had the universal code, but it deviated afterwards. I just wanted to make sure I was clear. And four, maybe you're thinking to yourself, why am I still listening to this podcast? And if you are, I get it. These are complicated topics, but you are doing amazing. You're learning the universal language of the cell. Other people brag about speaking Mandarin or French or Spanish, but you can always hit them with, oh yeah, how about the universal language bud? That one, every living thing on earth speaks. And this stuff matters more than sounding smart at parties. You remember the mRNA vaccine for COVID d. That's Mr. NA. The same messenger, RNA we just talked about. That's our Mary. I mean, now you can pick up a scientific paper about that and understand more than you could have four episodes ago. Bottom line, I'm proud of you for getting this far. This is not an easy subject and you've stuck with it for four episodes of you're awesome. And thank you for joining me on this biological journey. I'm Jackie Mullins, and this has been from Cells to Us. How See you again next time.