ATP Transport Challenges the Evolutionary Origin of Mitochondria

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By Fazale Rana – August 21, 2019

In high school, I spent most Sunday mornings with my family gathered around the TV watching weekly reruns of the old Abbott and Costello movies.

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Image: Bud Abbott and Lou Costello. Image credit: Wikipedia

One of my favorite routines has the two comedians trying to help a woman get her parallel-parked car out of a tight parking spot. As Costello takes his place behind the wheel, Abbott tells him to “Go ahead and back up.” And of course, confusion and hilarity follow as Costello repeatedly tries to clarify if he is to “go ahead” or “back up,” finally yelling, “Will you please make up your mind!”

As it turns out, biologists who are trying to account for the origin of mitochondria (through an evolutionary route) are just as confused about directions as Costello. Specifically, they are trying to determine which direction ATP transport occurred in the evolutionary precursors to mitochondria (referred to as pre-mitochondria).

In an attempt to address this question, a research team from the University of Virginia (UVA) has added to the frustration, raising new challenges for evolutionary explanations for the origin of mitochondria. Their work threatens to drive the scientific community off the evolutionary route into the ditch when it comes to explaining the origin of eukaryotic cells.1

To fully appreciate the problems this work creates for the endosymbiont hypothesis, a little background is in order. (For those familiar with the evidence for the endosymbiont hypothesis, you may want to skip ahead to The Role of Mitochondria.)

The Endosymbiont Hypothesis

Most biologists believe that the endosymbiont hypothesis serves as the best explanation for the origin of complex cells.

According to this idea, complex cells originated when symbiotic relationships formed among single-celled microbes after free-living bacterial and/or archaeal cells were engulfed by a “host” microbe.

The “poster children” of the endosymbiont hypothesis are mitochondria. Presumably, the mitochondria started its evolutionary journey as an endosymbiont. Evolutionary biologists believe that once engulfed by the host cell, this microbe took up permanent residency, growing and dividing inside the host. Over time, the endosymbiont and the host became mutually interdependent, with the endosymbiont providing a metabolic benefit for the host cell (such as providing a source of ATP). In turn, the host cell provided nutrients to the endosymbiont. Presumably, the endosymbiont gradually evolved into an organelle through a process referred to as genome reduction. This reduction resulted when genes from the endosymbiont’s genome were transferred into the genome of the host organism, generating the mitonuclear genome.

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Image: Endosymbiont Hypothesis. Image credit: Wikipedia

Evidence for the Endosymbiont Hypothesis

Much of the evidence for the endosymbiotic origin of mitochondria centers around the similarity between mitochondria and bacteria. These organelles are about the same size and shape as typical bacteria and have a double membrane structure like gram-negative cells. These organelles also divide in a way that is reminiscent of bacterial cells.

Biochemical evidence also exists for the endosymbiont hypothesis. Evolutionary biologists view the presence of the diminutive mitochondrial genome as a vestige of this organelle’s evolutionary history. They see the biochemical similarities between mitochondrial and bacterial genomes as further evidence for the evolutionary origin of these organelles.

The presence of the unique lipid, cardiolipin, in the mitochondrial inner membrane also serves as evidence for the endosymbiont hypothesis. This important lipid component of bacterial inner membranes is absent in the membranes of eukaryotic cells—except for the inner membranes of mitochondria. In fact, biochemists consider cardiolipin a signature lipid for mitochondria and a vestige of the organelle’s evolutionary history.

The Role of Mitochondria

Mitochondria serve cells in a number of ways, including:

  • Calcium storage
  • Calcium signaling
  • Signaling with reactive oxygen species
  • Regulation of cellular metabolism
  • Heat production
  • Apoptosis

Arguably one of the most important functions of mitochondria relates to their role in energy conversion. This organelle generates ATP molecules by processing the breakdown products of glycolysis through the tricarboxylic acid cycle and the electron transport chain.

Biochemists refer to ATP as a high-energy compound—it serves as an energy currency for the cell, and most cellular processes are powered by ATP. One way that ATP provides energy is through its conversion to ADP and an inorganic phosphate molecule. This breakdown reaction liberates energy that can be coupled to cellular activities that require energy.

 

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Image: The ATP/ADP Reaction Cycle. Image credit: Shutterstock

ATP Production and Transport

The enzyme complex ATP synthase, located in the mitochondrial inner membrane, generates ATP from ADP and inorganic phosphate, using a proton gradient generated by the flow of electrons through the electron transport chain. As ATP synthase generates ATP, it deposits this molecule in the innermost region of the mitochondria (called the matrix or the lumen).

In order for ATP to become available to power cellular processes, it has to be transported out of the lumen and across the mitochondrial inner membrane into the cytoplasm. Unfortunately, the inner mitochondrial membrane is impermeable to ATP (and ADP). In order to overcome this barrier, a protein embedded in the inner membrane called ATP/ADP translocase performs the transport operation. Conveniently, for every molecule of ATP transported out of the lumen, a molecule of ADP is transported from the cytoplasm into the lumen. In turn, this ADP is converted into ATP by ATP synthase.

Because of the importance of this process, copies of ATP/ADP translocase comprises 10% of the proteins in the inner membrane.

If this enzyme doesn’t function properly, it will result in mitochondrial myopathies.

The Problem ATP Transport Causes for The Endosymbiont Hypothesis

Two intertwined questions confronting the endosymbiont hypothesis relate to the evolutionary driving force behind symbiogenesis and the nature of pre-mitochondria.

Traditionally, evolutionary biologists have posited that the host cell was an anaerobe, while the endosymbiont was an aerobic microbe, producing ATP from lactic acid generated by the host cell. (Lactic acid is the breakdown product of glucose in the absence of oxygen).

But, as cell biologist Franklin Harold points out, this scenario has an inherent flaw. Namely, if the endosymbiont is producing ATP necessary for its survival from host cell nutrients, why would it relinquish some—or even all—of the ATP it produces to the host cell?

According to Harold, “The trouble is that unless the invaders share their bounty with the host, they will quickly outgrow him; they would be pathogens, not symbionts.”2

And, the only way they could share their bounty with the host cell is to transport ATP from the engulfed cell’s interior to the host cell’s cytoplasm. While mitochondria accomplish this task with the ATP/ADP translocase, there is no good reason to think that the engulfed cell would do this. Given the role ATP plays as the energy currency in the cell and the energy that is expended to make this molecule, there is no advantage for the engulfed cell to pump ATP from its interior to the exterior environment.

Harold sums up the problem this way: “Such a carrier would not have been present in the free-living symbiont but must have been acquired in the course of its enslavement; it cannot be called upon to explain the initial benefits of the association.”3

In other words, currently, there is no evolutionary explanation for why the ATP/ADP translocase in the mitochondrial inner membrane—a protein central to the role of mitochondria in eukaryotic cells—pumps ATP from the lumen to the cytoplasm.

Two Alternative Models

This problem has led evolutionary biologists to propose two alternative models to account for the evolutionary driving force behind symbiogenesis: 1) the hydrogen hypothesis; and 2) the oxygen scavenger hypothesis.

The hydrogen hypothesis argues that the host cell was a methanogenic member of archaea that consumed hydrogen gas and the symbiont was a hydrogen-generating alpha proteobacteria.

The oxygen-scavenging model suggests that the engulfed cell was aerobic, and because it used oxygen, it reduced the amount of oxygen in the cytoplasm of the host cell, thought to be an anaerobe.

Today, most evolutionary biologists prefer the hydrogen hypothesis—in part because the oxygen scavenger model, too, has a fatal flaw. As Harold points out, “This [oxygen scavenger model], too, is dubious, because respiration generates free radicals that are known to be a major source of damage to cellular membranes and genes.”4

Moving Forward, Or Moving Backward?

To help make headway, two researchers from UVA attempted to reconstruct the evolutionary precursor to mitochondria, dubbed pre-mitochondria.

Operating within the evolutionary framework, these two investigators reconstructed the putative genome of pre-mitochondria using genes in the mitochondrial genome and genes from the nuclear genomes of organisms they believe were transferred to the nucleus during the process of symbiogenesis. (Genes that clustered with alphaproteobacterial genes were deemed to be of mitochondrial origin.)

Based on their reconstruction, they conclude that the original engulfed cell actually used its ATP/ADP translocase to import ATP from the host cell cytoplasm into its interior, exchanging the ATP for an ADP. This is the type of ATP/ADP translocase found in obligate intracellular parasites alive today.

According to the authors, this means that:

“Pre-mitochondrion [was] an ‘energy scavenger’ and suggests an energy parasitism between the endosymbiont and its host at the origin of the mitochondria. . . . This is in sharp contrast with the current role of mitochondria as the cell’s energy producer and contradicts the traditional endosymbiotic theory that the symbiosis was driven by the symbiont supplying the host ATP.”5

The authors speculate that at some point during symbiogenesis the ATP/ADP translocase “went ahead and backed up,” reversing direction. But, this explanation is little more than a just-so story with no evidential support. Confounding their conjecture is their discovery that the ATP/ADP translocase found in mitochondria is evolutionarily unrelated to the ATP/ADP translocases found in obligate intracellular parasites.

The fact that the engulfed cell was an obligate intracellular parasite not only brings a halt to the traditional version of the endosymbiont hypothesis, it flattens the tires of both the oxygen scavenger model and hydrogen hypothesis. According to Wang and Wu (the UVA investigators):

“Our results suggest that mitochondria most likely originated from an obligate intracellular parasite and not from a free-living bacterium. This has important implications for our understanding of the origin of mitochondria. It implies that at the beginning of the endosymbiosis, the bacterial symbiont provided no benefits whatsoever to the host. Therefore we argue that the benefits proposed by various hypotheses (e.g, oxygen scavenger and hydrogen hypotheses) are irrelevant in explaining the establishment of the initial symbiosis.”6

If the results of the analysis by the UVA researchers stand, it leaves evolutionary biologists with no clear direction when it comes to determining the evolutionary driving force behind the early stages of symbiogenesis or the evolutionary route to mitochondria.

It seems that the more evolutionary biologists probe the question of mitochondrial origins, the more confusion and uncertainty results. In fact, there is not a coherent compelling evolutionary explanation for the origin of eukaryotic cells—one of the key events in life’s history. The study by the UVA investigators (along with other studies) casts aspersions on the most prominent evolutionary explanations for the origin of eukaryotes, justifying skepticism about the grand claim of the evolutionary paradigm: namely, that the origin, design, and history of life can be explained exclusively through evolutionary processes.

In light of this uncertainty, can the origin of mitochondria, and hence eukaryotic cells, be better explained by a creation model? I think so, but for many scientists this is a road less traveled.

Resources

Challenges to the Endosymbiont Hypothesis:

In Support of a Creation Model for the Origin of Eukaryotic Cells:

ATP Production and the Case for a Creator:

Endnotes
  1. Zhang Wang and Martin Wu, “Phylogenomic Reconstruction Indicates Mitochondrial Ancestor Was an Energy Parasite,” PLOS One 9, no. 10 (October 15, 2014): e110685, doi:10.1371/journal.pone.0110685.
  2. Franklin M. Harold, In Search of Cell History: The Evolution of Life’s Building Blocks (Chicago, IL: The University of Chicago Press, 2014), 131.
  3. Harold, In Search of Cell History, 131.
  4. Harold, In Search of Cell History, 132.
  5. Wang and Wu, “Phylogenomic Reconstruction.”
  6. Wang and Wu, “Phylogenomic Reconstruction.”

Reprinted with permission by the author

Original article at:
https://www.reasons.org/explore/blogs/the-cells-design/read/the-cells-design/2018/11/21/vocal-signals-smile-on-the-case-for-human-exceptionalism

Membrane Biochemistry Challenges Route to Evolutionary Origin of Complex Cells

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By Fazale Rana – July 10, 2019

Unfortunately, the same thing could be said to biologists trying to discover the evolutionary route that led to the emergence of complex, eukaryotic cells. No matter the starting point, it seems as if you just can’t get there from here.

This frustration becomes most evident as evolutionary biologists try to account for the biochemical makeup of the membranes found in eukaryotic cells. In my opinion, this struggle is not just an inconvenient detour. As the following paragraphs show, obstacles line the roadway, ultimately leading to a dead end that exposes the shortcomings of the endosymbiont hypothesis—a cornerstone idea in evolutionary biology.

Endosymbiont Hypothesis

Most biologists believe that the endosymbiont hypothesis stands as the best explanation for the origin of complex cells. According to this hypothesis, complex cells originated when symbiotic relationships formed among single-celled microbes after free-living bacterial and/or archaeal cells were engulfed by a “host” microbe.

The mitochondrion represents the “poster child” of the endosymbiont hypothesis. Presumably, this organelle started as an endosymbiont. Evolutionary biologists believe that once engulfed by the host cell, the microbe took up permanent residency, growing and dividing inside the host. Over time, the endosymbiont and host became mutually interdependent, with the endosymbiont providing a metabolic benefit—such as a source of ATP—for the host cell. In turn, the host cell provided nutrients to the endosymbiont. Presumably, the endosymbiont gradually evolved into an organelle through a process referred to as genome reduction. This reduction resulted when genes from the endosymbiont’s genome were transferred into the genome of the host organism.

Evidence for the Endosymbiont Hypothesis
1. Most of the evidence for the endosymbiont hypothesis centers around mitochondria and their similarity to bacteria. Mitochondria are about the same size and shape as a typical bacterium and have a double membrane structure like gram-negative cells. These organelles also divide in a way that is reminiscent of bacterial cells.

2. Biochemical evidence also exists for the endosymbiont hypothesis. Evolutionary biologists view the presence of the diminutive mitochondrial genome as a vestige of this organelle’s evolutionary history. They see the biochemical similarities between mitochondrial and bacterial genomes as further evidence for the evolutionary origin of these organelles.

3. The presence of the unique lipid, cardiolipin, in the mitochondrial inner membrane also serves as evidence for the endosymbiont hypothesis. This important lipid component of bacterial inner membranes is not found in the membranes of eukaryotic cells—except for the inner membranes of mitochondria. In fact, biochemists consider it a signature lipid for mitochondria and a vestige of the organelle’s evolutionary history. So far, the evolutionary route looks well-paved and clear.

Discovery of Lokiarchaeota

Evolutionary biologists have also developed other lines of evidence in support of the endosymbiont hypothesis. For example, biochemists have discovered that the genetic core (DNA replication and the transcription and translation of genetic information) of eukaryotic cells resembles that of the archaea. This similarity suggests to many biologists that a microbe belonging to the archaeal domain served as the host cell that gave rise to eukaryotic cells.

Life scientists think they may have determined the identity of that archaeal host. In 2015, a large international team of collaborators reported the discovery of Lokiarchaeota, a new phylum belonging to the archaea. This phylum clusters with eukaryotes on the evolutionary tree. Analysis of the genomes of Lokiarchaeota identifies a number of genes involved in membrane-related activities, suggesting that this microbe may well have possessed the ability to engulf other microbes.1 At this point, it looks like “you can get there from here.”

Challenges to the Endosymbiont Hypothesis

Despite this seemingly compelling evidence, the evolutionary route to the first eukaryotic cells is littered with potholes. I have written several articles detailing some of the obstacles. (See Challenges to the Endosymbiont Hypothesis in the Resources section.) Also, a divide on the evolutionary roadway called the lipid divide compounds the problem for the endosymbiont hypothesis.

Lipid Divide

The lipid divide refers to the difference in the chemical composition of the cell membranes found in bacteria and archaea. Phospholipids comprise the cell membranes of both sorts of microbes. But the similarity ends there. The chemical makeup of the phospholipids is distinct in bacteria and archaea.

Bacterial phospholipids are built around a d-glycerol backbone, which has a phosphate moiety bound to the glycerol in the sn-3 position. Two fatty acids are bound to the d-glycerol backbone at the sn-1 and sn-2 positions. In water, these phospholipids assemble into bilayer structures.

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Figure: Difference between archaeal (top) and bacterial (middle and bottom) phospholipids. Features include 1: isoprene chains, 2: ether linkage, 3: l-glycerol, 4 and 8: phosphate group, 5: fatty acid chains, 6: ester linkages, 7: d-glycerol, 9: lipid bilayer of bacterial membranes, 10: lipid monolayer found in some archaea. Image credit: Wikipedia

Archaeal phospholipids are constructed around an l-glycerol backbone (which produces membrane lipids with different stereochemistry than bacterial phospholipids). The phosphate moiety is attached to the sn-1 position of glycerol. Two isoprene chains are bound to the sn-2 and sn-3 positions of l-glycerol via ether linkages. Some archaeal membranes are formed from phospholipid bilayers, while others are formed from phospholipid monolayers.

Presumably, the structural features of the archaeal phospholipids serve as an adaptation that renders them ideally suited to form stable membranes in the physically and chemically harsh environments in which many archaea find themselves.

Lipid Divide Frustrates the Origin of Eukaryotic Cell Membranes

In light of the lipid divide and the evidence that seemingly indicates that the endosymbiotic host cell likely belonged to Lokiarchaeota, it logically follows that the membrane composition of eukaryotic cells should be archaeal-like. But, this expectation is not met and the evolutionary route encounters another pothole. Instead, the cell membranes of eukaryotic cells closely resemble bacterial membranes.

One way to repair the roadway is to posit that during the evolutionary process that led to the emergence of eukaryotic cells, a transition from archaeal-like membranes to bacterial-like membranes took place. In fact, supporting evidence comes from laboratory studies demonstrating that stable bilayers can form from a mixture of bacterial and archaeal phospholipids, even though the lipids from the two sources have opposite stereochemistry.

Evolutionary biologists Purificación López-García and David Moreira question if evidence can be marshaled in support of this scenario for two reasons.2 First, mixing of phospholipids in the lab is a poor model for cell membranes that function as a “dynamic cell-environment interface.”3

Second, they question if this transition is feasible given how exquisitely optimized membrane proteins must be to fit into cell membranes. The nature of protein optimization is radically different for bacterial and archaeal membranes. Because cell membrane systems are optimized, the researchers question if an adequate driving force for this transition exists.

In other words, these two scientists express serious doubts about the biochemical viability of a transitional stage between archaeal membranes. In light of these obstacles, López-García and Moreira write, “The archaea-to-bacteria membrane shift remains the Achilles’ heel for these models [that propose an archaeal host for endosymbionts].”4

In other words, you can’t get there from here.

Can Lokiarchaeota Traverse the Lipid Divide?

In the midst of this uncertain evolutionary route, a recent study by investigators from the Netherlands seems to point the way toward the evolutionary origin of eukaryotic membranes.5 Researchers screened the Lokiarchaeota genome for enzymes that would take part in phospholipid synthesis with the hope of finding clues about how this transition may have occurred. They conclude that this group of microbes could not make l-glycerol-1-phosphate (a key metabolic intermediate in the production of archaeal phospholipids) because it lacked the enzyme glycerol-1-phosphate dehydrogenase (G1PDH). They also discovered evidence that suggests that this group of microbes could make fatty acids and chemically attach them to sugars. The researchers argue that Lokiarchaeota could make some type of hybrid phospholipid with features of both archaeal and bacterial phospholipids.

The team’s approach to understanding how evolutionary processes could bridge the lipid divide and account for the origin of eukaryotic membranes is clever and inventive, to be sure. But it is far from convincing for at least four reasons.

1. Absence of evidence is not evidence of absence, as the old saying goes. Just because the research team didn’t find the gene for G1PDH in the Lokiarchaeota genetic material doesn’t mean this microbe didn’t have the capacity to make archaeal-type phospholipids. Toward this end, it is important to note that researchers have not cultured any microbe that belongs to this group organisms. The group’s existence is inferred from metagenomic analysis, which involves isolating small fragments of DNA from the environment (in this case a hydrothermal vent system in the Atlantic Ocean, called Loki’s Castle) and stitching them together into a genome. The Lokiarchaeota “genome” is low quality (1.4-fold coverage) and incomplete (8 percent of the genome is missing). Around one-third (32 percent) of the genome codes for proteins with unknown function. Could it be that an enzyme capable of generating l-glycerol-1-phosphate exists in the mysterious third of the genome? Or in the missing 8 percent?

2. While the researchers discovered that genes could conceivably work together to make d-glycerol-3-phosphate (though the enzymes encoded by these genes perform different metabolic functions), they found no direct evidence that Lokiarchaeota produces d-glycerol-3-phosphate. Nor did they find evidence for glycerol-3-phosphate dehydrogenase (G3PDH) in the Lokiarchaeota genetic material. This enzyme plays a key role in the synthesis of phospholipids in bacteria.

3. Though the researchers found evidence that Lokiarchaeota had the capacity to make fatty acids, some of the genes required for the process seem to have been acquired by these microbes via horizontal gene transfer with genetic material from bacteria. (It should be noted that 29 percent of the Lokiarchaeota genome comes from the bacteria.) It is not clear when Lokiarchaeota acquired these genes and, therefore, if this metabolic capability has any bearing on the origin of eukaryotes.

4. The researchers present no evidence that Lokiarchaeota possessed the protein machinery that would chemically attach isoprenoid lipids to d-glycerol-3-phosphate via ether linkages.

Thus, the only way to establish Lokiarchaeota membranes as a transitional evolutionary pathway between those found in Archaea and Bacteria is to perform chemical analysis of its membranes. At this juncture, such analysis is impossible to perform because no one has been able to culture Lokiarchaeota. In fact, other evidence suggests that this group of microbes possessed archaeal-type membranes. Researchers have recovered archaeal lipids in the sediments surrounding Loki’s Castle, but they have not recovered bacterial-like lipids.

More Lipid Divide Frustration

Given these problems, could it be that the host microbe for the endosymbiont was a member of Bacteria, not Archaea? While this model would solve the problem of the lipid divide, it leaves unexplained the similarity between the genetic core of eukaryotes and the Archaea. Nor does it account for the grouping of eukaryotes with the Archaea.

It doesn’t look like you can get there from here, either.

Evolutionary biologists Jonathan Lombard, Purificación López-García and David Moreira sum things up when they write, “The origin of eukaryotic membranes is a problem that is rarely addressed by the different hypotheses that have been proposed to explain the emergence of eukaryotes.”6 Yet, until this problem is adequately addressed, the evolutionary route to eukaryotes will remain obscure and the endosymbiont hypothesis noncompelling.

In light of this challenge and others, maybe a better way to make sense of the origin of eukaryotic cells is to view them as the Creator’s handiwork. For many scientists, it is a road less traveled, but it accounts for all of the data. You can get there from here.

Resources

Challenges to the Endosymbiont Hypothesis

Support for a Creation Model for the Origin of Eukaryotic Cells

Endnotes
  1. Anja Spang et al., “Complex Archaea that Bridge the Gap between Prokaryotes and Eukaryotes,” Nature 521 (May 14, 2015): 173–79, doi:10.1038/nature14447; Katarzyna Zaremba-Niedzwiedzka et al., “Asgard Archaea Illuminate the Origin of Eukaryotic Cellular Complexity,” Nature 541 (January 19, 2017): 353–58, doi:10.1038/nature21031.
  2. Purificación López-García and David Moreira, “Open Questions on the Origin of Eukaryotes,” Trends in Ecology and Evolution 30, no. 11 (November 2015): 697–708, doi:10.1016/j.tree.2015.09.005.
  3. López-García and Moreira, “Open Questions.”
  4. López-García and Moreira, “Open Questions.”
  5. Laura Villanueva, Stefan Schouten, and Jaap S. Sinninghe Damsté, “Phylogenomic Analysis of Lipid Biosynthetic Genes of Archaea Shed Light on the ‘Lipid Divide,’” Environmental Microbiology 19, no. 1 (January 2017): 54–69, doi:10.1111/1462-2920.13361.
  6. Jonathan Lombard, Purificación López-García, and David Moreira, “The Early Evolution of Lipid Membranes and the Three Domains of Life,” Nature Reviews Microbiology 10 (June 11, 2012): 507–15, doi:10.1038/nrmicro2815.

Reprinted with permission by the author

Original article at:
https://www.reasons.org/explore/blogs/the-cells-design/read/the-cells-design/2018/11/21/vocal-signals-smile-on-the-case-for-human-exceptionalism

Why Mitochondria Make My List of Best Biological Designs

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BY FAZALE RANA – MAY 1, 2019

A few days ago, I ran across a BuzzFeed list that catalogs 24 of the most poorly designed things in our time. Some of the items that stood out from the list for me were:

  • serial-wired Christmas lights
  • economy airplane seats
  • clamshell packaging
  • juice cartons
  • motion sensor faucets
  • jewel CD packaging
  • umbrellas

What were people thinking when they designed these things? It’s difficult to argue with BuzzFeed’s list, though I bet you might add a few things of your own to their list of poor designs.

If biologists were to make a list of poorly designed things, many would probably include…everything in biology. Most life scientists are influenced by an evolutionary perspective. Thus, they view biological systems as inherently flawed vestiges cobbled together by a set of historically contingent mechanisms.

Yet as our understanding of biological systems improves, evidence shows that many “poorly designed” systems are actually exquisitely assembled. It also becomes evident that many biological designs reflect an impeccable logic that explains why these systems are the way they are. In other words, advances in biology reveal that it makes better sense to attribute biological systems to the work of a Mind, not to unguided evolution.

Based on recent insights by biochemist and origin-of-life researcher Nick Lane, I would add mitochondria to my list of well-designed biological systems. Lane argues that complex cells and, ultimately, multicellular organisms would be impossible if it weren’t for mitochondria.1(These organelles generate most of the ATP molecules used to power the operations of eukaryotic cells.) Toward this end, Lane has demonstrated that mitochondria’s properties are just-right for making complex eukaryotic cells possible. Without mitochondria, life would be limited to prokaryotic cells (bacteria and archaea).

To put it another way, Nick Lane has shown that prokaryotic cells could never evolve the complexity needed to form cells with complexity akin to the eukaryotic cells required for multicellular organisms. The reason has to do with bioenergetic constraints placed on prokaryotic cells. According to Lane, the advent of mitochondria allowed life to break free from these constraints, paving the way for complex life.

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Figure 1: A Mitochondrion. Image credit: Shutterstock

Through Lane’s discovery, mitochondria reveal exquisite design and logical architecture and operations. Yet this is not necessarily what I (or many others) would have expected if mitochondria were the result of evolution. Rather, we’d expect biological systems to appear haphazard and purposeless, just good enough for the organism to survive and nothing more.

To understand why I (and many evolutionary biologists) would hold this view about mitochondria and eukaryotic cells (assuming that they were the product of evolutionary processes), it is necessary to review the current evolutionary explanation for their origins.

The Endosymbiont Hypothesis

Most biologists believe that the endosymbiont hypothesis is the best explanation for the origin of complex eukaryotic cells. This hypothesis states that complex cells originated when single-celled microbes formed symbiotic relationships. “Host” microbes (most likely archaea) engulfed other archaea and/or bacteria, which then existed inside the host as endosymbionts.

The presumption, then, is that organelles, including mitochondria, were once endosymbionts. Evolutionary biologists believe that, once engulfed, the endosymbionts took up permanent residency within the host cell and even grew and divided inside the host. Over time, the endosymbionts and the host became mutually interdependent. For example, the endosymbionts provided a metabolic benefit for the host cell, such as serving as a source of ATP. In turn, the host cell provided nutrients to the endosymbionts. The endosymbionts gradually evolved into organelles through a process referred to as genome reduction. This reduction resulted when genes from the endosymbionts’ genomes were transferred into the genome of the host organism.

Based on this scenario, there is no real rationale for the existence of mitochondria (and eukaryotic cells). They are the way they are because they just wound up that way.

But Nick Lane’s insights suggest otherwise.

Lane’s analysis identifies a deep-seated rationale that accounts for the features of mitochondria (and eukaryotic cells) related to their contribution to cellular bioenergetics. To understand why mitochondria and eukaryotic cells are the way they are, we first need to understand why prokaryotic cells can never evolve into large complex cells, a necessary step for the advent of complex multicellular organisms.

Bioenergetics Constraints on Prokaryotic Cells

Lane has discovered that bioenergetics constraints keep bacterial and archaeal cells trapped at their current size and complexity. Key to discovering this constraint is a metric Lane devised called Available Energy per Gene (AEG). It turns out that AEG in eukaryotic cells can be as much as 200,000 times larger than the AEG in prokaryotic cells. This extra energy allows eukaryotic cells to engage in a wide range of metabolic processes that support cellular complexity. Prokaryotic cells simply can’t afford such processes.

An average eukaryotic cell has between 20,000 to 40,000 genes; a typical bacterial cell has about 5,000 genes. Each gene encodes the information the cell’s machinery needs to make a distinct protein. And proteins are the workhorse molecules of the cell. More genes mean a more diverse suite of proteins, which means greater biochemical complexity.

So, what is so special about eukaryotic cells? Why don’t prokaryotic cells have the same AEG? Why do eukaryotic cells have an expanded repertoire of genes and prokaryotic cells don’t?

In short, the answer is: mitochondria.

On average, the volume of eukaryotic cells is about 15,000 times larger than that of prokaryotic cells. Eukaryotic cells’ larger size allows for their greater complexity. Lane estimates that for a prokaryotic cell to scale up to this volume, its radius would need to increase 25-fold and its surface area 625-fold.

Because the plasma membrane of bacteria is the site for ATP synthesis, increases in the surface area would allow the hypothetically enlarged bacteria to produce 625 times more ATP. But this increased ATP production doesn’t increase the AEG. Why is that?

The bacteria would have to produce 625 times more proteins to support the increased ATP production. Because the cell’s machinery must access the bacteria’s DNA to make these proteins, a single copy of the genome is insufficient to support all of the activity centered around the synthesis of that many proteins. In fact, Lane estimates that for bacteria to increase its ATP production 625-fold, it would require 625 copies of its genome. In other words, even though the bacteria increased in size, in effect, the AEG remains unchanged.

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Figure 2: ATP Production at the Cell Membrane Surface. Image credit: Shutterstock

Things become more complicated when factoring in cell volume. When the surface area (and concomitant ATP production) increase by a factor of 625, the volume of the cell expands 15,000 times. To satisfy the demands of a larger cell, even more copies of the genome would be required, perhaps as many as 15,000. But energy production tops off at a 625-fold increase. This mismatch means that the AEG drops by 25 percent per gene. For a genome consisting of 5,000 genes, this drop means that a bacterium the size of a eukaryotic cell would have about 125,000 times less AEG than a typical eukaryotic cell and 200,000 times less AEG when compared to eukaryotes with genome sizes approaching 40,000 genes.

Bioenergetic Freedom for Eukaryotic Cells

Thanks to mitochondria, eukaryotic cells are free from the bioenergetic constraints that ensnare prokaryotic cells. Mitochondria generate the same amount of ATP as a bacterial cell. However, their genome consists of only 13 proteins, thus the organelle’s ATP demand is low. The net effect is that the mitochondria’s AEG skyrockets. Furthermore, mitochondrial membranes come equipped with an ATP transport protein that can pump the vast excess of ATP from the organelle interior into the cytoplasm for the eukaryotic cell to use.

To summarize, mitochondria’s small genome plus its prodigious ATP output are the keys to eukaryotic cells’ large AEG.

Of course, this raises a question: Why do mitochondria have genomes at all? Well, as it turns out, mitochondria need genomes for several reasons (which I’ve detailed in previous articles).

Other features of mitochondria are also essential for ATP production. For example, cardiolipinin the organelle’s inner membrane plays a role in stabilizing and organizing specific proteinsneeded for cellular energy production.

From a creation perspective it seems that if a Creator was going to design a eukaryotic cell from scratch, he would have to create an organelle just like a mitochondrion to provide the energy needed to sustain the cell’s complexity with a high AEG. Far from being an evolutionary “kludge job,” mitochondria appear to be an elegantly designed feature of eukaryotic cells with a just-right set of properties that allow for the cellular complexity needed to sustain complex multicellular life. It is eerie to think that unguided evolutionary events just happened to traverse the just-right evolutionary path to yield such an organelle.

As a Christian, I see the rationale that undergirds the design of mitochondria as the signature of the Creator’s handiwork in biology. I also view the anthropic coincidence associated with the origin of eukaryotic cells as reason to believe that life’s history has purpose and meaning, pointing toward the advent of complex life and humanity.

So, now you know why mitochondria make my list.

Resources

Endnotes
  1. Nick Lane, “Bioenergetic Constraints on the Evolution of Complex Life,” Cold Spring Harbor Perspectives in Biology 6, no. 5 (May 2014): a015982, doi:10.1101/cshperspect.a015982.

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Original article at:
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Endosymbiont Hypothesis and the Ironic Case for a Creator

endosymbionthypothesisandtheironic

BY FAZALE RANA – DECEMBER 12, 2018

i ·ro ·ny

The use of words to express something different from and often opposite to their literal meaning.
Incongruity between what might be expected and what actually occurs.

—The Free Dictionary

People often use irony in humor, rhetoric, and literature, but few would think it has a place in science. But wryly, this has become the case. Recent work in synthetic biology has created a real sense of irony among the scientific community—particularly for those who view life’s origin and design from an evolutionary framework.

Increasingly, life scientists are turning to synthetic biology to help them understand how life could have originated and evolved. But, they have achieved the opposite of what they intended. Instead of developing insights into key evolutionary transitions in life’s history, they have, ironically, demonstrated the central role intelligent agency must play in any scientific explanation for the origin, design, and history of life.

This paradoxical situation is nicely illustrated by recent work undertaken by researchers from Scripps Research (La Jolla, CA). Through genetic engineering, the scientific investigators created a non-natural version of the bacterium E. coli. This microbe is designed to take up permanent residence in yeast cells. (Cells that take up permanent residence within other cells are referred to as endosymbionts.) They hope that by studying these genetically engineered endosymbionts, they can gain a better understanding of how the first eukaryotic cells evolved. Along the way, they hope to find added support for the endosymbiont hypothesis.1

The Endosymbiont Hypothesis

Most biologists believe that the endosymbiont hypothesis (symbiogenesis) best explains one of the key transitions in life’s history; namely, the origin of complex cells from bacteria and archaea. Building on the ideas of Russian botanist Konstantin Mereschkowski, Lynn Margulis(1938–2011) advanced the endosymbiont hypothesis in the 1960s to explain the origin of eukaryotic cells.

Margulis’s work has become an integral part of the evolutionary paradigm. Many life scientists find the evidence for this idea compelling and consequently view it as providing broad support for an evolutionary explanation for the history and design of life.

According to this hypothesis, complex cells originated when symbiotic relationships formed among single-celled microbes after free-living bacterial and/or archaeal cells were engulfed by a “host” microbe. Presumably, organelles such as mitochondria were once endosymbionts. Evolutionary biologists believe that once engulfed by the host cell, the endosymbionts took up permanent residency, with the endosymbiont growing and dividing inside the host.

Over time, the endosymbionts and the host became mutually interdependent. Endosymbionts provided a metabolic benefit for the host cell—such as an added source of ATP—while the host cell provided nutrients to the endosymbionts. Presumably, the endosymbionts gradually evolved into organelles through a process referred to as genome reduction. This reduction resulted when genes from the endosymbionts’ genomes were transferred into the genome of the host organism.

endosymbiont-hypothesis-and-the-ironic-case-for-a-creator-1

Figure 1: Endosymbiont hypothesis. Image credit: Wikipedia.

Life scientists point to a number of similarities between mitochondria and alphaproteobacteria as evidence for the endosymbiont hypothesis. (For a description of the evidence, see the articles listed in the Resources section.) Nevertheless, they don’t understand how symbiogenesis actually occurred. To gain this insight, scientists from Scripps Research sought to experimentally replicate the earliest stages of mitochondrial evolution by engineering E. coli and brewer’s yeast (S. cerevisiae) to yield an endosymbiotic relationship.

Engineering Endosymbiosis

First, the research team generated a strain of E. coli that no longer has the capacity to produce the essential cofactor thiamin. They achieved this by disabling one of the genes involved in the biosynthesis of the compound. Without this metabolic capacity, this strain becomes dependent on an exogenous source of thiamin in order to survive. (Because the E. coli genome encodes for a transporter protein that can pump thiamin into the cell from the exterior environment, it can grow if an external supply of thiamin is available.) When incorporated into yeast cells, the thiamin in the yeast cytoplasm becomes the source of the exogenous thiamin, rendering E. coli dependent on the yeast cell’s metabolic processes.

Next, they transferred the gene that encodes a protein called ADP/ATP translocase into the E. coli strain. This gene was harbored on a plasmid (which is a small circular piece of DNA). Normally, the gene is found in the genome of an endosymbiotic bacterium that infects amoeba. This protein pumps ATP from the interior of the bacterial cell to the exterior environment.2

The team then exposed yeast cells (that were deficient in ATP production) to polyethylene glycol, which creates a passageway for E. coli cells to make their way into the yeast cells. In doing so, E. coli becomes established as endosymbionts within the yeast cells’ interior, with the E. coli providing ATP to the yeast cell and the yeast cell providing thiamin to the bacterial cell.

Researchers discovered that once taken up by the yeast cells, the E. coli did not persist inside the cell’s interior. They reasoned that the bacterial cells were being destroyed by the lysosomal degradation pathway. To prevent their destruction, the research team had to introduce three additional genes into the E. coli from three separate endosymbiotic bacteria. Each of these genes encodes proteins—called SNARE-like proteins—that interfere with the lysosomal destruction pathway.

Finally, to establish a mutualistic relationship between the genetically-engineered strain of E. coli and the yeast cell, the researchers used a yeast strain with defective mitochondria. This defect prevented the yeast cells from producing an adequate supply of ATP. Because of this limitation, the yeast cells grow slowly and would benefit from the E. coli endosymbionts, with the engineered capacity to transport ATP from their cellular interior to the exterior environment (the yeast cytoplasm.)

The researchers observed that the yeast cells with E. coli endosymbionts appeared to be stable for 40 rounds of cell doublings. To demonstrate the potential utility of this system to study symbiogenesis, the research team then began the process of genome reduction for the E. coli endosymbionts. They successively eliminated the capacity of the bacterial endosymbiont to make the key metabolic intermediate NAD and the amino acid serine. These triply-deficient E. coli strains survived in the yeast cells by taking up these nutrients from the yeast cytoplasm.

Evolution or Intentional Design?

The Scripps Research scientific team’s work is impressive, exemplifying science at its very best. They hope that their landmark accomplishment will lead to a better understanding of how eukaryotic cells appeared on Earth by providing the research community with a model system that allows them to probe the process of symbiogenesis. It will also allow them to test the various facets of the endosymbiont hypothesis.

In fact, I would argue that this study already has made important strides in explaining the genesis of eukaryotic cells. But ironically, instead of proffering support for an evolutionary origin of eukaryotic cells (even though the investigators operated within the confines of the evolutionary paradigm), their work points to the necessary role intelligent agency must have played in one of the most important events in life’s history.

This research was executed by some of the best minds in the world, who relied on a detailed and comprehensive understanding of biochemical and cellular systems. Such knowledge took a couple of centuries to accumulate. Furthermore, establishing mutualistic interactions between the two organisms required a significant amount of ingenuity—genius that is reflected in the experimental strategy and design of their study. And even at that point, execution of their experimental protocols necessitated the use of sophisticated laboratory techniques carried out under highly controlled, carefully orchestrated conditions. To sum it up: intelligent agency was required to establish the endosymbiotic relationship between the two microbes.

endosymbiont-hypothesis-and-the-ironic-case-for-a-creator-2

Figure 2: Lab researcher. Image credit: Shutterstock.

Or, to put it differently, the endosymbiotic relationship between these two organisms was intelligently designed. (All this work was necessary to recapitulate only the presumed first step in the process of symbiogenesis.) This conclusion gains added support given some of the significant problems confronting the endosymbiotic hypothesis. (For more details, see the Resources section.) By analogy, it seems reasonable to conclude that eukaryotic cells, too, must reflect the handiwork of a Divine Mind—a Creator.

Resources

Endnotes

  1. Angad P. Mehta et al., “Engineering Yeast Endosymbionts as a Step toward the Evolution of Mitochondria,” Proceedings of the National Academy of Sciences, USA 115 (November 13, 2018): doi:10.1073/pnas.1813143115.
  2. ATP is a biochemical that stores energy used to power the cell’s operation. Produced by mitochondria, ATP is one of the end products of energy harvesting pathways in the cell. The ATP produced in mitochondria is pumped into the cell’s cytoplasm from within the interior of this organelle by an ADP/ATP transporter.
Reprinted with permission by the author
Original article at:
https://www.reasons.org/explore/blogs/the-cells-design/read/the-cells-design/2018/12/12/endosymbiont-hypothesis-and-the-ironic-case-for-a-creator

Mitochondria’s Deviant Genetic Code: Evolution or Creation?

mitochondriasdeviantgeneticcode

BY FAZALE RANA – APRIL 18, 2018

When I was in high school, I had the well-deserved reputation of being a wise guy—though the people who knew me then might have preferred to call me a wise—, instead. Either way, for being a wise guy, I sure didn’t display much wisdom during my teenage years.

I would like to think that I am wiser today. But, the little wisdom I do possess didn’t come easy. To quote singer and songwriter, Helen Reddy, “It’s wisdom born of pain.”

Life’s hardships sure have a way of teaching you lessons. But, I also learned that there is a shortcut to gaining wisdom—if you are wise enough to recognize it. (See what I did there?) It is better to solicit the advice of wise people than to gain wisdom through life’s bitter experiences. And, perhaps there was no wiser person ever than Solomon. Thankfully, Solomon’s wisdom was captured in the book of Proverbs. Many of life’s difficulties can be sidestepped if we are willing to heed Solomon’s advice.

Solomon gained his wisdom through observation and careful reflection. But, his wisdom also came through divine inspiration, and according to Solomon, it was through wisdom that God created the world in which we live (Proverbs 8:22–31). And, it is out of this wisdom that the Holy Spirit inspired Solomon to offer the insights found in the Proverbs.

In Psalm 104, the Psalmist (presumably David) echoes the same idea as Solomon: God created our world through wisdom. The Psalmist writes:

How many are your works, Lord!

In wisdom you made them all;

Based on Proverbs 8 and Psalm 104, I would expect God’s wisdom to be manifested in the created order. The Creator’s fingerprints—so evident in nature—should not only reflect the work of intelligent agency but also display undeniable wisdom. In my view, that wisdom should be reflected in the elegance, cleverness, and ingenuity of the designs seen throughout nature. Designs that reflect an underlying purpose. And these features are exactly what we observe when we study the biological realm—as demonstrated by recent work on aquatic mammal body size conducted by investigators from Stanford University.1

Body Sizes of Aquatic Mammals

Though the majority of the world’s mammals live in terrestrial habitats, the most massive members of this group reside in Earth’s oceans. For evolutionary biologists, common wisdom has it that the larger size of aquatic mammals reflects fewer evolutionary constraints on their body size because they live in the ocean. After all, the ocean habitat is more expansive than those found on land, and aquatic animals don’t need to support their weight because they are buoyed by the ocean.

As it turns out, common wisdom is wrong in this case. Through the use of mathematical modeling (employing body mass data from about 3,800 living species of aquatic mammals and around 3,000 fossil species), the research team from Stanford learned that living in an aquatic setting imposes tight constraints on body size, much more so than when animals live on land. In fact, they discovered (all things being equal) that the optimal body mass for aquatic mammals is around 1,000 pounds. Interestingly, the body mass distributions for members of the order Sirenia (dugongs and manatees), and the clades Cetacea (whales and dolphins), and Pinnipeds (sea lions and seals) cluster near 1,000 pounds.

Scientists have learned that the optimal body mass of aquatic mammals displays an underlying biological rationale and logic. It reflects a trade-off between two opposing demands: heat retention and caloric intake. Because the water temperatures of the oceans are below mammals’ body temperatures, heat retention becomes a real problem. Mammals with smaller bodies can’t consume enough food to compensate for heat loss to the oceans, and they don’t have the mass to retain body heat. The way around this problem is to increase their body mass. Larger bodies do a much better job at retaining heat than do smaller bodies. But, the increase in body mass can’t go unchecked. Maintaining a large body requires calories. At some point, metabolic demands outpace the capacity for aquatic mammals to feed, so body mass has to be capped (near 1,000 pounds).

The researchers noted a few exceptions to this newly discovered “rule.” Baleen whales have a body mass that is much greater than 1,000 pounds. But, as the researchers noted, these creatures employ a unique feeding mechanism that allows them to consume calories needed to support their massive body sizes. Filter feeding is a more efficient way to consume calories than hunting prey. The other exception is creatures such as otters. The researchers believe that their small size reflects a lifestyle that exploits both aquatic and terrestrial habitats.

Argument for God’s Existence from Wisdom

The discovery that the body mass of aquatic mammals has been optimized is one more example of the many elegant designs found in biological systems—designs worthy to be called the Creator’s handiwork. However, from my perspective, this optimization also reflects the Creator’s sagacity as he designed mammals for the purpose of living in the earth’s oceans.

But, instead of relying on intuition alone to make a case for a Creator, I want to present a formal argument for God’s existence based on the wisdom of biology’s designs. To make this argument, I follow after philosopher Richard Swinburne’s case for God’s existence based on beauty. Swinburne argues, “If God creates a universe, as a good workman he will create a beautiful universe. On the other hand, if the universe came into existence without being created by God, there is no reason to suppose that it would be a beautiful universe.”2 In other words, the beauty in the world around us signifies the Divine.

In like manner, if God created the universe, including the biological realm, we should expect to see wisdom permeating the designs in nature. On the other hand, if the universe came into being without God’s involvement, then there is no reason to think that the designs in nature would display a cleverness and ingenuity that affords a purpose—a sagacity, if you will. In fact, evolutionary biologists are quick to assert that most biological designs are flawed in some way. They argue that there is no purpose that undergirds biological systems. Why? Because evolutionary processes do not produce biological systems from scratch, but from preexisting systems that are co-opted through a process dubbed exaptation (by the late evolutionary biologist Stephen Jay Gould), and then modified by natural selection to produce new designs.3 According to biologist Ken Miller:

“Evolution . . . does not produce perfection. The fact that every intermediate stage in the development of an organ must confer a selective advantage means that the simplest and most elegant design for an organ cannot always be produced by evolution. In fact, the hallmark of evolution is the modification of pre-existing structures. An evolved organism, in short, should show the tell-tale signs of this modification.”4

And yet we see designs in biology that are not just optimized, but characterized by elegance, cleverness, and ingenuity—wisdom.

Truly, God is a wise guy.

Resources

Endnotes

  1. William Gearty, Craig R. McClain, and Jonathan L. Payne, “Energetic Tradeoffs Control the Size Distribution of Aquatic Mammals,” Proceedings of the National Academy of Sciences USA (March 2018): doi:10.1073/pnas.1712629115.
  2. Richard Swinburne, The Existence of God, 2nd ed. (New York: Oxford University Press, 2004), 190–91.
  3. Stephen Jay Gould and Elizabeth S. Vrba, “Exaptation: A Missing Term in the Science of Form,” Paleobiology8 (January 1, 1982): 4–15, doi:10.1017/S0094837300004310.
  4. Kenneth R. Miller, “Life’s Grand Design,” Technology Review 97 (February/March 1994): 24–32.
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Original article at:
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Can a Creation Model Explain the Origin of Mitochondria?

canacreationmodelexplaintheorigin

BY FAZALE RANA – NOVEMBER 23, 2016

Some called her a scientific heretic. Others were a bit more kind, describing her as a maverick.

Lynn Margulis (1938–2011) earned her reputation in the late 1960s when she proposed the endosymbiont hypothesis for the origin of eukaryotic cells. Because her ideas about evolution didn’t conform to Darwinian principles, evolutionary biologists summarily dismissed her idea out of hand and then went on to ignore her work for a couple of decades. She was ultimately vindicated, however, as the endosymbiont hypothesis gradually gained acceptance.

Today, Margulis’s proposal has become a cornerstone idea of the evolutionary paradigm and is taught in introductory high school and college biology courses. This classroom exposure explains why I am often asked about the endosymbiont hypothesis when I speak on university campuses. Many first-year biology students and professional life scientists alike find the evidence for this idea compelling, and consequently view it as providing broad support for an evolutionary explanation for the history and design of life.

Yet, new work by biochemists from Cambridge University make it possible to account for the origin of eukaryotic cells from a creation model perspective, providing a response to the endosymbiont hypothesis.1

The Endosymbiont Hypothesis

According to this hypothesis, complex cells originated when symbiotic relationships formed among single-celled microbes after free-living bacterial and/or archaeal cells were engulfed by a “host” microbe. (Ingested cells that take up permanent residence within other cells are referred to as endosymbionts.)

Accordingly, organelles, such as mitochondria, were once endosymbionts. Once taken inside the host cell, the endosymbionts presumably took up permanent residency within the host, with the endosymbionts growing and dividing inside the host. Over time, the endosymbionts and the host became mutually interdependent, with the endosymbionts providing a metabolic benefit for the host cell. The endosymbionts gradually evolved into organelles through a process referred to as genome reduction. This reduction resulted when genes from the endosymbionts’ genomes were transferred into the genome of the host organism. Eventually, the host cell evolved both the machinery to produce the proteins needed by the former endosymbiont and the processes needed to transport those proteins into the organelle’s interior.

Evidence for the Endosymbiont Hypothesis

The main line of evidence for the endosymbiont hypothesis is the similarity between organelles and bacteria. For example, mitochondria—which are believed to be descended from a group of α-proteobacteria—are about the same size and shape as a typical bacterium and have a double membrane structure like gram-negative cells. These organelles also divide in a way that is reminiscent of bacterial cells.

There is also biochemical evidence for the endosymbiont hypothesis. Evolutionary biologists view the existence of the diminutive mitochondrial genome as a vestige of this organelle’s evolutionary history. Additionally, the biochemical similarities between mitochondrial and bacterial genomes are taken as further evidence for the evolutionary origin of these organelles.

The presence of the unique lipid called cardiolipin in the mitochondrial inner membrane also serves as evidence for the endosymbiont hypothesis. Cardiolipin is an important lipid component of bacterial inner membranes, yet it is not found in the membranes of eukaryotic cells—except for the inner membranes of mitochondria. In fact, biochemists consider it a signature lipid for mitochondria and a vestige of this organelle’s evolutionary history.

A Creation Model Perspective on Mitochondria

So, as a creationist, how do I make sense of the evidence for the endosymbiont hypothesis?

Instead of focusing my efforts on refuting the endosymbiont hypothesis, here, I take a different approach. I maintain that it is reasonable to view eukaryotic cells as the work of a Creator, with the shared similarities between mitochondria and bacteria reflecting common design rather than common descent.

However, to legitimately interpret mitochondrial origins from a creation model perspective, there must be a reason for the biochemical similarities between mitochondria and bacteria. Previously, I wrote about discoveries that provide a rationale for why mitochondria have their own genomes. (See “Resources.”) Thanks to recent research advances, an explanation now exists for why the mitochondrial inner membranes harbor cardiolipin.

Cardiolipin’s Function

Previous studies identified close associations between cardiolipin and a number of proteins found in the mitochondrial inner membrane. These proteins play a role in harvesting energy for the cell to use. Compared to other lipid components found in the inner membrane, cardiolipin appears to preferentially associate with these proteins. Evidence indicates that cardiolipin helps to stabilize the structures of these proteins and serves to organize the proteins into larger functional complexes within the membrane.2 In fact, several studies have implicated defects in cardiolipin metabolism in the onset of a number of neuromuscular disorders.

The work of the Cambridge University investigators adds to this insight. These researchers were using computer simulations to model the interactions between cardiolipin and a protein complex called F1-F0 ATPase. Embedded within the inner membrane of mitochondria, this complex is a biomolecular rotary motor that produces the compound ATP—an energy storage material the cell’s machinery uses to power its operations.

Like other proteins found in the inner membrane, cardiolipin forms a close association with F1-F0 ATPase. However, instead of permanently binding to the surface of the protein complex, cardiolipin dynamically interacts with this membrane-embedded protein complex. The researchers think that this dynamic association and the unusual chemical structure of cardiolipin (which gives it the flexibility to interact with a protein surface) are critical for its role within the mitochondrial inner membrane. As it turns out, cardiolipin not only stabilizes the F1-F0 ATPase complex (as it does for other inner membrane proteins), but it also lubricates the protein’s rotor, allowing it to turn in the viscous cell membrane environment. Also, its unique structure helps move protons through the F1-F0 ATPase motor, providing the electrical power to operate this biochemical motor.

The bottom line: There is an exquisite biochemical rationale for why cardiolipin is found in mitochondrial inner membranes (and bacterial membranes). In light of this new insight, it is reasonable to view the shared similarities between these organelles and bacteria as reflecting common design—the product of the Creator’s handiwork. Like most biological systems, this organelle appears to be designed for a purpose.

Resources
Why Do Mitochondria Have DNA?” by Fazale Rana (article)
Mitochondrial Genomes: Evidence for Evolution or Creation?” by Fazale Rana (article)
Complex Protein Biogenesis Hints at Intelligent Design” by Fazale Rana (article)
Archetype or Ancestor? Sir Richard Owen and the Case for Design” by Fazale Rana (article)
Nanodevices Make Megascopic Statement” by Fazale Rana (article)

Endnotes

  1. Anna Duncan, Alan Robinson, and John Walker, “Cardiolipin Binds Selectively but Transiently to Conserved Lysine Residues in the Rotor of Metazoan ATP Synthases,” Proceedings of the National Academy of Sciences USA 113 (August 2016): 8687–92, doi:10.1073/pnas.1608396113.
  2. Giuseppe Paradies et al., “Functional Role of Cardiolipin in Mitochondrial Bioenergetics,” Biochimica et Biophysica Acta—Bioenergetics 1837 (April 2014): 408–17, doi:10.1016/j.bbabio.2013.10.006.
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Original article at:
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