[00:00:00] Speaker A: Foreign the Future, a podcast about evolution and intelligent Design.
[00:00:11] Speaker B: Welcome to ID the Future. I'm your host, Andrew McDermott. Well, today I continue a four episode series with Dr. Jonathan McClatchy on the Intelligent design and irreducible complexity of eukaryotic cell division.
[00:00:25] Speaker C: But before we get to that good stuff, let me tell you about an upcoming event you'll want to be a part of. From the smallest honeybee to the greatest whale, planet Earth is swarming with creatures of all shapes and sizes, each intelligently designed for their habitats. Where did they all come from and what are the implications for a faith in God? Join us at the 7th Annual Dallas Conference on Science and Faith on February 8, 2025 in Denton, Texas, or via livestream for a stimulating series of talks on the theme All Creatures Great and Small. Whether you join us in the Dallas area or online, you'll learn about the Miracle of Butterfly Metamorphosis with Paul Nelson, the Amazing Honeybee with Eric Hedin, the Scientific Evidence of the Human Soul with Michael Egnor, the Intelligent Design of Plants with Emily and Daniel Reeves, the Theory of ID as Fuel for Scientific Discovery with with Casey Luskin and the Origin of Animal Body Plans with Stephen Meyer. In addition to these in person, attendees can choose from special breakout sessions presented by John West, Richard Sternberg, George Montanez, Ray Bolan, and Stephen Dilley. Other perks to joining in person include a live musical performance on the theme of the conference, a conference bookstore with a large selection of titles by Discovery Institute scientists and scholars, a free book in honor of the late Jonathan Wells, opportunities for book signings with the speakers, and exhibitor tables from our partner organizations. You can learn more and register for the
[email protected] that's scienceandfaith.com Dr. Jonathan McClatchy.
[00:02:05] Speaker B: Is a fellow and resident biologist at the Discovery Institute's center for Science and Culture. He was previously an assistant professor at Sattler College in Boston, where he lectured biology for four years. McClatchy holds a bachelor's degree in forensic biology, a master's degree in evolutionary biology, a second master's degree in medical and molecular bioscience, and a PhD in evolutionary biology. His research interests include the scientific evidence of design in nature, arguments for the existence of God, and New Testament scholarship. Jonathan is also founder and director of talkaboutdoubts.com welcome back, Jonathan.
[00:02:43] Speaker A: Great to be here.
[00:02:45] Speaker B: Well, we're talking about a subject you've studied closely for several the Eukaryotic Cell Division cycle. You've published several articles about it at evolutionnews.org, which is our flagship news and commentary site that covers the debate over evolution and the evidence for intelligent design. In those posts, you detail the exquisite engineering and design manifested by the cycle and its control systems. You've also recently published a review paper on the topic in the journal Bio Complexity, and I should note that the paper is freely available so listeners can click the link in the show Notes for this episode and dive deeper than we're able to go on this podcast.
In Part one of this series that you and I are doing, you set us up with some basics and explained why various components of the mitotic cell division apparatus exhibit something called irreducible complexity. Today we're going to take a closer look at the intricate mechanics of eukaryotic cell division, focusing on the mitotic spindle, the structure and function of microtubules, and the roles of various motor proteins in the division cycle.
And listeners, if you're someone who has stumbled across the Idea the Future podcast and you haven't been listening long, don't get scared away by our occasional discussion of some of the technical aspects of design. In order to understand why Darwinian evolutionary theory struggles to account for the origin and development of life on Earth, and why intelligent design is a better explanation, we have to be willing to wade into the complexity a bit. Famed biologist and atheist Richard Dawkins has said that if evolution is not gradual, it ceases to have any explanatory power at all. And Darwin himself offered up a criterion of failure for his theory of natural selection when he first proposed it in 1859. Darwin said this if it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous successive slight modifications, my theory would absolutely break down.
And biochemist Michael Behe has written that in order to understand the barriers to evolution, we have to bite the bullet of complexity. And so that's exactly what we're doing here on ID the Future, as well as
[email protected] and in the papers, articles, books and videos that we produce. We're inviting you to dip a toe in the ocean of ingenuity, as Brazilian chemist Dr. Marcos Eberlin puts it in his book Foresight Ingenuity that in our universal experience is wedded to a power unique to intelligent agents. And that's foresight.
So, Jonathan, let's jump in. While keeping it as accessible to the layperson as we can, first, remind us of the difference between eukaryotes and prokaryotes.
[00:05:32] Speaker A: Sure, so a eukaryotic cell has a nucleus, whereas prokaryotic cells don't. Prokaryotes is an umbrella term for bacteria and archaea.
Eukaryotes characteristically have membrane enclosed or membrane bound organelles, whereas prokaryotes don't. And they differ dramatically in their mode of cell division as well.
[00:05:56] Speaker B: Okay, and when we talk about the eukaryotic cell cycle, what are we talking about? Exactly.
[00:06:02] Speaker A: So we're talking about the process by which the cell divides, which culminates in what we call M phase, which is mitosis and cytokinesis, which is a final step in cell division, where the cell bifurcates into two daughter cells. And mitosis is the process by which the DNA, the chromosomes, are segregated in preparation for the cell dividing.
[00:06:32] Speaker B: Yeah. So this really is a process that lies at the heart of life and all cell division, at least in the eukaryotes. Exactly, yeah. So a crucial aspect of mitosis is the movement of chromosomes where the genetic information is stored, the DNA. And the molecular machinery responsible for this delicate task is something known as the mitotic spindle. Can you describe this molecular machinery for us?
[00:06:58] Speaker A: Sure. So the, the process of mitosis involves a number of different phases. You've got prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis. And as I said before, mitosis is the process that accomplishes the segregation of the genetic material. And so, for example, during metaphase, which is midway through mitosis, the chromosomes, which have their condensed characteristic chromosome structure, are aligned along the equatorial plane of the cell, and they are bound by spindle fibers, also known as microtubules, which bind to protein complexes known as kinetochores in the middle of the chromosome. And during anaphase, the sister chromatids pull apart and they, they, they are driven or pulled towards the holes of the cell by these microtubules.
And this allows the chromosomes to be segregated as the cell is dividing. And this is absolutely crucial because failure to accomplish proper separation of those cystic chromatids during mitosis can result in aneuploidy where the daughter cell ends up with the wrong number of chromosomes, which of course, can result in abnormalities, including cancer. And so this is absolutely crucial for the process of cell division.
[00:08:45] Speaker B: Okay. And along with the mitotic spindle, we have what's known as motor proteins, and they assist in the assembly and function of the spindle. Tell us about the motor proteins.
[00:08:57] Speaker A: Yeah. So one of the functions of motor proteins in the cell is their role or their function in assembling the mitotic spindle during eukaryotic cell division. So you can imagine a robotic factory that assembles and organizes the cell in preparation for undergoing division. And it helps to facilitate the controlled segregation of the genetic material into the daughter cells. So the motor proteins that are involved in the organization of the mitotic spindle can be divided into four main classes. You've got Kinesin 5, Kinesin 14, Kinesin 4 and 10, and Dynein. So Kinesin 5 is directed towards the plus end, and it slides apart those microtubules that have their polarities oriented in opposite directions, that is anti parallel microtubules. And so kinesin 5 contributes to spindle elongation and bipolarity by pushing apart the spindle poles. Whereas, on the other hand, Kinesin 14 motors are directed towards the minus end of microtubules. And they each possess one motor domain in addition to other domains that associate with a different microtubule. And they cross link antiparallel interpolar microtubules at the spindle mid zone, and thereby they pull the poles towards one another. Another group of kinesins, kinesin 4 and kinesin 10, which are known collectively as chromokinesins, play an important role in the positioning and segregation of chromosomes during mitosis as well. And so the job of these chromokinesins is to move the chromosomes to their proper positions, such that each daughter cell will receive the appropriate number of chromosomes. And a final group of motor proteins that are involved in mitosis are the dyneins that have their motor domains associated with the microtubules, which radiate from the centrosomes. And they're cargo binding domains bound to proteins that are embedded in the cell cortex. And the movement of dynein exerts a pulling force on the microtubules on the microtubule minus ends, and it pulls the centrosomes in the direction of the cell cortex. And this movement ensures that each daughter cell receives a complete set of chromosomes.
So that that is essentially how motor proteins function in the process of mitosis.
[00:11:27] Speaker B: Right. And, you know, as we're discussing this and learning about it, it's very important to try to get some visual aids. And as you write in your articles, you do have some animation that you can take a look at. And listeners, I do encourage you to pull up Jonathan's articles on these and get a feel visually for what we're talking about here. And of course, many of us will have seen kinesin, the motor protein kinesin, in action, thanks to the animation video that the center for Science and Culture has produced. That's the one that walks step by step, placing one foot in front of the other as it transports materials along a microtubule highway in the cell. My kids love to watch those molecular machine videos, especially that one. And of course, they're all freely available on our YouTube channel, Discovery Science. So how does the motor protein dynein move compared to that kinesin protein?
[00:12:21] Speaker A: Yeah, I second what you said about the aid that is given by visuals such as animations and figures and so forth. I actually created a figure which is found in my Evolution news article on the role of motor proteins in cell division. So I'd refer listeners to that figure to get more of a feel for how this works in the context of mitosis. But as to your question. So kinesin typically moves in the direction of the plus end of the microtubule. So that's towards the periphery of the cell. And then dynein generally moves towards the minus end of the microtubule, that is towards the cell center.
So kinesis and motor proteins walk step by step by placing one friend in front of the other, as we see in the animation that the center for Science and Culture produced that you already alluded to, Whereas dynein moves more by a swinging cross bridge mechanism.
[00:13:19] Speaker B: Yeah, yeah, yeah. And listeners, I'm serious, just go and go onto YouTube and look up Discovery Science. That's where all our videos are located. And type in kinesin K I n E S I N and watch this thing work. It's amazing. Well, the rapid polymerizing and depolymerizing of the spindle filaments is a phenomenon that's known as catastrophe and rescue. Interesting names for those. Tell us more about that part of the process.
[00:13:48] Speaker A: Sure. So in the early mitotic stages, microtubules assemble and disassemble rapidly. And this is mediated by the addition and removal of tubulin heterodimers. And this is known as dynamic instability, which is the.
And the process of depolymerization and polymerization are known as catastrophe and rescue, respectively.
And so microtubules probe the cell until they encounter their target and which is one of the kinetochores that's embedded on a chromosome around the centromere. And the regulation of microtubule catastrophe and rescue is linked to the hydrolysis of guanosine triphosphate, or gtp, which is a nucleotide that's bound to tubulin within the microtubule lattice. And each tubule subunit is able to bind to one Molecule of gtp. And during polymerization, the tubulin subunits that are bound to GTP are added to the growing end of the microtubule, forming a GTP cap, which stabilizes the microtubule and promotes growth. And as the microtubule continues to polymerize, the GDP bound tubulin subunits undergo hydrolysis. And this converts GTP to GDP or guanosine diphosphate. And once hydrolyzed, the tubule and subunits become less stable and the microtubule is more prone to depolymerization. And upon reaching a critical concentration of GDP bound tubulin at the microtubule end, catastrophe occurs. And that leads to the rapid depolymerization of the microtubule. And microtubule rescue involves the exchange of GDP bound tubulin for GTP band chippelin, which promotes microtubule growth. And there are certain cellular factors, including microtubule associated proteins and motor proteins that can facilitate that process by promoting the incorporation of GTP bound tubulin or by protecting the GTP cap from hydrolysis. So, for example, kinesin H proteins are plus N directed motor proteins that destabilize microtubules. Another motor protein, kinesin 13, is bidirectional, so it's able to move in the direction of either the plus or the minus end of microtubules, in contrast to most motor proteins that are unidirectional.
So they're able to promote the depolymerization of a microtubule from both ends. And this activity of kinesin 13 proteins is regulated by distinct targeting to regions of the spindle, by regulatory phosphorylation events and by interactions with different binding partners. And these astonishing kinesin 13 motors bind the end of the microtubule, and they trigger a conformational change that results in the depolymerization of the microtubule.
[00:16:52] Speaker B: Okay. And, you know, one of the things that's so interesting about these processes is the dynamic, engineered nature of them. Many of these components are not just lying around collecting dust somewhere in the cell. No, these things are built as they're needed, thanks to instructions in the cell's DNA to turn on or turn off certain proteins at certain times. Is that an accurate way to kind of look at it?
[00:17:16] Speaker A: Yes, that's absolutely right. They're expressed as needed, and they come together to.
To drive and regulate and control the eukaryotic cell division system.
[00:17:32] Speaker B: Yeah. So this spindle connects to the chromosomes and also gently pulls them apart at the right time, ensuring that each daughter cell receives a complete set of chromosomes. Is that what's happening?
[00:17:45] Speaker A: Yeah, exactly. So the, the, as I said before, during metaphase, during mitosis, the.
The chromosomes, as you. These two sister chromatid. Two sister chromatids that are connected together at the centromere are aligned along the equatorial plane of the cell, or the midpoint of the cell. And then during anaphase, the sister chromatids break apart and they're pulled by the microtubules, or spindle fibers, towards the poles of the cell. And this facilitates chromosome segregation in preparation for cytokinesis, which is the endpoint of the cell division machinery, where the cell is split into two daughter cells.
[00:18:33] Speaker B: Yeah. And that split, you know, might sound simple to our layperson ears, but this is a life and death process that happens constantly in, in biological life. And, you know, it's. It's one of those where you commit to splitting and you can't go back, you know, and then there's different controls to assure that the process succeeds at that point, because it is literally life or death when you're turning into two cells from one. Now, if the average person were able to peer inside a cell and observe these molecular machines and this delicate process happening at nanoscale, it's likely that someone would immediately ascribe it to design. But adherents of a Darwinian evolutionary framework would have us credit this astounding phenomenon to a blind, purposeless process, as you like to say, that strains credulity. Why is it so hard to credit neo Darwinism with eukaryotic cell division?
[00:19:35] Speaker A: Yeah, so as we've talked about previously, cell division in eukaryotes, and also bacteria for that matter, is irredistibly complex. And you require multiple different components, well matched, specifically crafted parts that have to work together in unison to bring about the higher level objective of performing cell division. And if any of those parts were missing, then you don't have a system that works half as well as used to or as well as it used to, but it's broken. And an important part, part or aspect of that irresistible complexity when it comes to mitosis is the role of these motor proteins and indeed the spindle microtubules as well. Without those motor proteins, without these spindle microtubules performing as they do, there could be no cell division in the manner that it is performed by eukaryotic cells.
[00:20:30] Speaker B: Yeah, yeah. Okay, fascinating. Well, in our next episode in this series, we're going to focus on the checkpoints that ensure the success of this process.
This will really bring into focus more of the engineering aspects involved in cell Division. Jonathan, where can listeners turn for more information on this?
[00:20:50] Speaker A: Sure. So you could read my paper that came out in the journal Biocomplexity towards the end of last year. You go to the Biocomplexity website and pull it up there, download a PDF. I've also got multiple blog posts on the design of the card Excel Division machinery on Evolution News and Science Today. Just go to evolutionnews.org and if you, if you move your mouse over writers and select my name, Jonathan McClatchy, you'll find an archive of my articles there and you can look up my articles relating to the cell division machinery. There's also only, so far as I know, one textbook that is fully dedicated to the cardiac cell cycle, which I recommend. It's getting a little dated at this point, but it's a really great textbook. It's called the Cell Cycle Principles of Control by David Morgan. And so I'd recommend that too as an introduction to this fascinating topic.
[00:21:48] Speaker B: Yeah, yeah. Okay. That's awesome. EvolutionNews.org to find Jonathan's articles and of course in the show notes for this episode, I'll also link to his review paper at the journal Bio Complexity.
So we'll have it all linked for you. Just gotta find it. Well, Jonathan, this is part two of our four part series on the eukaryotic Cel cycle. I'm excited to continue unpacking this complexity and the design that's inherent in this amazing system. And you know, if you want more of Jonathan's work and writing beyond Cell Division, you can look up his website as well. Jonathanmcclatchy.com well, that's it for now for ID the Future. I'm Andrew McDermott. Join us again soon. Thanks for listening.
[00:22:38] Speaker C: Visit
[email protected] and intelligent design.org this program.
[00:22:44] Speaker A: Is copyright Discovery Instagram Institute and recorded by its center for Science and Culture.
