No metaphor is perfect, but the most iconic metaphor in biology, the metaphor that might be the only thing you remember from high school biology, is one that conveys almost no information at all. I am talking about calling mitochondria the “powerhouse.”
When the lights go out in a storm, no one ever says, “There must be a problem down at the old powerhouse.” If you see cooling towers in the distance as you drive down the highway, no one says, “Look at the big powerhouse over there.” The bruiser on the hockey team might be called a powerhouse. So could someone who is frequently promoted in the corporation.
But how does the term “powerhouse” explain anything about mitochondria?
Presumably, the point of the metaphor is that as an electricity generating station produces useful energy for a city, the mitochondria produce useful energy for the cell. There is something there. That is true and useful for what it is. But mitochondria are so much more. They dictate our every breath. They tie us to our ecosystem at the molecular level. They remind us of our complicated evolutionary history. They are so much more than a powerhouse. When teaching the mitochondria, or any topic, it is necessary to hide some of the complexity so that our students can enter into the conversation, but we need to do so in a way that invites them into beauty inherent to our content. We want clarity that leads to curiosity, not reductionism that offers overly simple answers.
In a very real way, we breathe for the sake of our mitochondria. When we inhale, we breathe in the oxygen that our bodies need, certainly. But the part of our body that needs that oxygen is our mitochondria. The whole of our circulatory system is artfully constructed to carry the oxygen we breathe to every corner of our bodies, into every cell, and into every mitochondrion. It is our mitochondria that use the oxygen. Their ability to harness energy for the cell (in the form of a molecule called ATP) depends on our ability to provide them with the oxygen they need. The process is called oxidative respiration. They respire our oxygen. Or maybe we respire their oxygen.
And the same is true with each exhale. The carbon dioxide that we breathe out was made by those same mitochondria. They are burning our fuel—our food—and in turn releasing the carbon dioxide that is left over. The carbon dioxide drifts into our circulatory system and back to the lungs where it can vent from the body. We can hold our breath for as long as we are able but the buildup of carbon dioxide will eventually force us to exhale again, one way or another. With each breath in and each breath out, we do their bidding.
With their critical role in the cell of burning fuel, using oxygen, making ATP they are the key linkage point that ties us to the broader ecosystem. Mitochondria are one half of a biochemical cycle. They use oxygen and make carbon dioxide. The chloroplasts in plants are the other half of the cycle. They do the opposite, using carbon dioxide and making oxygen. Only when our mitochondria work together with the green things of the world does the sustainable cycle at the heart of our biochemistry come into view. There is no self-made man or independent woman. Each of us, through our mitochondria, is tied at the molecular level, to the grass, trees, fruits, and vegetables of the world. We may know cognitively that we are tied to these things, but it is through our mitochondria that the ties are most concrete.
Finally, our mitochondria are a window into the beauty and mystery of our biology. Our mitochondria are domesticated bacteria. They have their own DNA and their own molecular machinery. Their membranes look like bacterial membranes. When the cell needs more mitochondria, we don’t make them, the mitochondria just reproduce. It is almost like our cells are infected with them.
The explanation for this unusual cellular partnership is called the endosymbiosis theory, which proposes an extraordinary origin for the complex cells that make up plants, animals, and human beings. It says that long ago one cell ate another, ingested it, but did not digest it, or break it down. Instead, the two cells each found an advantage to the new arrangement. The cell that was eaten was now protected from further predation. As its predator continued to eat, it delivered fuel to the inner cell. The outer cell found that its new parasite sometimes had leftover molecular energy to share. This is a history so unlikely, so absurd, that is thought to be one of the most significant hurdles to clear for intelligent life to develop at all. But there they are. In each cell, a little swimming reminder that a God who can do the impossible has no problem whatsoever with the highly improbable.
God breathed into Adam’s nostrils, and that holy wind was then breathed in by Adam’s mitochondria. It was Adam’s mitochondria that made the carbon dioxide that he then breathed out. Humans are part of this world, part of the ecology of Earth, and it is through our mitochondria that we are woven at the biological level into the rest of God’s good world. In our mitochondria—as they breathe, swim, and reproduce within our cells—we have a living monument to God’s ability to work through the most improbable of events. How dare we belittle and obscure this beauty by merely calling it a powerhouse. As educators we need to simplify and clarify, but we also need to avoid reductionism that strips the beauty and mystery from our content.
Maybe a better metaphor would be, “The mitochondria is the Ebenezer of the cell.” Mitochondria should be a reminder of our dependence on the rest of life on our planet. They should be a marker of where God did a wondrous thing. If we called the mitochondria the Ebenezer of the cell, then we could remember, with every breath, the wonderful work of God displayed in our very cells.
Great essay! Really enjoyed the quality of the writing also, along with the points he’s making. As a scientist Christian who teaches Biology, I similarly try to get across to students – whether majors or non-majors in science – how we are truly fearfully and wonderfully made, as the Psalm expresses so well. I always try to introduce the Scriptural view of God’s sovereign will, that extends to both miracles and working thru providence, that God can choose to work thru miraculous healing or medicine – and also thru the processes of evolution and however God chose to set humanity apart to bear his image. It’s been liberating to many students; some who never considered the claims of Christ.
But re “powerhouse”. Like Clayton, it’s always struck me as cheesy. In introductory courses, I like to begin with how we moved from alchemy to modern science, by case studies of Galileo, and then Antoine and Marie-Anne Lavoisier, and the collapse of the Four Element Model of the universe. Oxidation (the addition of oxygen to an element or molecule, rather than the Element “Fire” leaving it) was one of their discoveries that changed science and the world. So when we move on to study cells, I like to call the mitochondria the furnace of the house: their breakfast bagel is getting fed into the little furnace where it’s oxidized and the energy released, used for other purposes, including keeping our bodies warm and alive.
Of course, “furnace of the house” perhaps isn’t as good a metaphor for tropical countries!
Maybe they remind you of our evolutionary history but when I see the design of the electron transport chain and the F1F0ATP Synthase molecular machine that is largely made in ribosomes outside the mitochondria and then transported inside, piece by piece, by chaperones I see God’s hand. This happened by random, unguided, blind chance? “I am fearfully and wonderfully made.”
I prefer to see the evolutionary process itself as a product of God’s creative power. Evolution is not entirely random, but is rather driven by survival, metabolism, sex, errors specific to genetic copying, and an ever growing complex of biological structure that is reused, duplicated, and repurposed over trillions of generations. There are numerous biologists working out the evolutionary pathways leading to ATP synthase. Such work is not only integral to biology, but vital in working out the pathways of current evolution, such as the constant adaptation of disease causing microorganisms and protein structures. Evolution is one of God’s tools for fearfully and wonderfully making us.
A rich and rewarding explanation of God’s amazing creation of evolution, and the part it played in the emergence of mitochondria. We cannot know if this was the first biological mutualism to arise, but mutualism is now ubiquitous in the biology of the world from the necessary bacteria in our own bodies to the cooperation of fungi and algae in lichens. The complex life made possible through chloroplasts and mitochondria may be the most instrinsic biological systems to arise through mutualism, but the power of evolution to give rise to complex, mutually sustaining ecosystems is, as the author showcases, a psalm to God’s creation.