Chapter Content
Okay, so, you know, life, right? It all starts with one single cell. And get this, that first cell, it just divides in half, then those two divide into four, and it just keeps going like that. Like, bam, bam, bam, multiplying like crazy. Apparently, after about 47 doublings – which, uh, is a lot – you end up with something like a hundred quadrillion cells. Yeah, a hundred quadrillion! That's like 1 followed by 17 zeros, you know? And that's supposedly enough to, like, form a person. Crazy, right?
Of course, I guess, you know, cells die off along the way. So, that number's just, like, a really, really, really rough estimate. And honestly, you’ll find different numbers depending on where you look. But the point is, from the second that egg gets fertilized until, well, until you’re not around anymore, each one of these cells, like, totally knows its job.
And here's the thing, your cells? They know way more about you than you even know about yourself. Each cell carries this whole set of genetic instructions – your body's instruction manual, basically. So, it not only knows how to do its own thing, but it also, like, understands how everything else works in your body, too. You never have to remind your cells to keep an eye on their adenosine triphosphate levels, or like, where to stash extra folic acid. I mean, they’re doing all this stuff, plus, like, millions of other things you can’t even imagine.
Each cell is really something. Like, seriously a miracle of nature. Even the simplest cell is, like, incredibly complex. Way beyond anything humans could ever create. For instance, even just building a basic yeast cell, get this, you need, like, as many parts as it takes to build a Boeing 777 jet airplane. And then you’ve gotta cram all that into this tiny little sphere that's only five micrometers across, and, and then somehow you gotta make the whole thing reproduce!
But, you know, human cells? They're on a whole other level compared to yeast cells. Way more diverse and way more complex, that’s for sure.
Your body is basically like a country with a hundred quadrillion citizens – those cells. And each one is working for the, you know, the good of the whole. They do everything for you. They make you feel happy, they let you think, they let you stand and stretch and jump around. When you eat, they, like, grab the nutrients, produce energy, get rid of waste. All the stuff you learned about in high school biology, you know? And they even make sure you get hungry in the first place and feel good after you eat so you remember to eat again. They grow your hair, they make earwax, they keep your brain humming along silently. They manage every single nook and cranny of you. When you're threatened, they defend you. They even sacrifice themselves for you – billions of them every single day. And yet, how often do you stop to thank them? So, yeah, maybe we should all just, like, take a moment and appreciate our amazing cells.
How exactly do they do all this stuff? How do they store fat, how do they make insulin, how do they do everything else that keeps something as complicated as you going? We know a little bit, but, honestly, it's just a tiny fraction. There are, like, at least 200,000 different kinds of proteins buzzing around in your body. And we only understand, I don't know, maybe two percent of them? It’s probably a little more, but not much.
The things that go on in the cellular world are constantly surprising us. Like, nitric oxide, right? In nature, it's this really nasty, toxic gas, a major air pollutant. So, in the 1980s, when scientists discovered that our own cells were constantly producing this stuff, they were, like, whoa, what's going on here? At first, they couldn't figure out what it was doing. Then they found out it was, like, everywhere – controlling blood flow and energy levels, attacking cancer and other diseases, regulating our sense of smell, even helping guys get erections! That also explained why nitroglycerin, you know, that stuff they use in dynamite, could relieve chest pain. It gets converted to nitric oxide in the blood, relaxing the muscles in the blood vessels and letting the blood flow more easily. So, in less than ten years, this gas went from being a dangerous environmental toxin to, like, a miracle cure inside our bodies.
You've got "around a few hundred" different types of cells, with all kinds of different sizes and shapes. Nerve cells can be like, super long and stringy, stretching up to a meter. Red blood cells are shaped like discs. And photoreceptor cells, the ones that help us see, they're shaped like rods. Cell size varies a lot, too. You know, the moment of conception? That’s an image, since the sperm is facing off against an egg that's, like, 85,000 times bigger than it is. But on average, a human cell is only about 20 micrometers wide. That's like, only about two percent of a millimeter. Super small, almost invisible, but big enough to hold thousands of complex structures like mitochondria, and millions and millions of molecules. And cells, well, they vary in their vitality too. Your skin cells, for example, they're all dead. Which is, yeah, kinda gross to think about, right? That the whole surface of your body is dead. If you're an average-sized adult, you're walking around with about two kilograms of dead skin, and shedding billions of tiny flakes every single day. If you wipe your finger across a dusty shelf, that line is mostly made of dead skin.
Most cells only live for, like, a month or so. But there are some exceptions. Liver cells can last for years, even though their internal parts are constantly being replaced every few days. Brain cells, on the other hand, they stick around for as long as you do. You're born with about a hundred billion of them, and that's the most you'll ever have. It's estimated you lose about 500 an hour. So, yeah, you really shouldn't waste a minute. Although, the components of your brain cells are constantly being renewed too, so, like liver cells, your brain cells effectively only last for about a month. It's thought that actually, every part of you is, like, different from how it was nine years ago. So, yeah, at a cellular level, we’re all pretty young.
So, the first person to actually describe cells was Robert Hooke, right? The guy who argued with Isaac Newton over who discovered the inverse square law of planetary motion. He only lived until 68, but he accomplished a lot in his life. He was a skilled theorist, but also a master of making precision instruments. But he's most famous for his book, “Micrographia,” which he did back then, in which he showed the public a microscopic world that was so incredibly complex and diverse and cleverly designed that it was beyond anything anyone had ever imagined.
Hooke was the first to spot all these tiny cavities in plants. He called them "cells" because they reminded him of monks' cells, you know, their little individual rooms. He even calculated that there were something like 195 million of these cells in a square inch of cork. That was a crazy huge number for science at the time. Microscopes had been around for a generation or so, but Hooke’s were, like, seriously good. They could magnify things 30 times, which was incredible for 17th-century technology.
So, just ten years later, when Hooke and the other members of the Royal Society in London got these images and reports from a linen draper in Delft, the Netherlands, a guy named Antoni van Leeuwenhoek, who used a microscope that could magnify things 275 times, they were understandably pretty surprised. Despite having almost no formal education or scientific background, Leeuwenhoek was, like, this incredibly keen and dedicated observer and, like, a total technical genius.
Even today, nobody really knows how he managed to build such powerful microscopes using just simple, handcrafted devices. His microscopes were basically just tiny pieces of glass set into wooden fittings. More like magnifying glasses, really, but not really, you know? Leeuwenhoek would build a new instrument for every single experiment. And he kept his techniques super secret, although he did give the English some hints about how to improve resolution.
For 50 years – unbelievably, he didn’t even start until he was in his 40s – he sent almost 200 reports to the Royal Society, all written in Low Dutch, the only language he spoke. Leeuwenhoek just listed what he found and included some incredibly detailed drawings, but no explanations. He reported on pretty much anything he could get his hands on – bread mold, bee stingers, blood cells, teeth, hair, his own saliva, semen, and even poop, although he did apologize for the smell when he mentioned the last two. Almost none of this had ever been seen under a microscope before.
In one report, Leeuwenhoek claimed that he'd found these tiny "animalcules" in a sample of pepper-water infusion. It took the Royal Society a year to actually find these "little animals" using all the best equipment England had to offer. What Leeuwenhoek had discovered was protozoa. And he estimated that there were, like, 8,280,000 of these things in a single drop of water, which was more than the entire population of the Netherlands. The world was just crawling with life, way more and in ways that nobody had ever imagined.
Leeuwenhoek’s amazing discoveries really inspired other people to start peering into microscopes. Sometimes a little too keenly, and they ended up seeing things that weren’t really there. This Dutch researcher claimed he saw “little preformed people” inside sperm cells, and he called these tiny beings "homunculi." For a while, a lot of people actually believed that all humans, and really all creatures, were just, like, miniature, complete versions of their parents. Leeuwenhoek himself also indulged in his personal interests. In one of his less successful experiments, he tried to study the explosive properties of gunpowder by, like, observing a small explosion really close up. He almost blinded himself!
Leeuwenhoek discovered bacteria in 1683. But because of the limitations of microscope technology, things kinda stalled there for, like, a century and a half. It wasn't until 1831 that someone actually saw the cell nucleus for the first time. That was this Scottish guy named Robert Brown. In 1839, someone finally realized that the cell was the basic building block of all life. That was, uh, a discovery by a German guy, Theodor Schwann. It was actually pretty late in the game for such a fundamental realization. And it wasn’t really widely accepted at first. It wasn’t until the 1860s, thanks to the work of Louis Pasteur, that it was, like, conclusively proven that life can’t just spontaneously generate, but has to come from pre-existing cells. This became known as the cell theory, and it’s the foundation of all modern biology.
Cells have been compared to all kinds of things, from "a complex chemical refinery," to "a densely populated metropolis." They're both and neither. They're like a refinery because there's a massive amount of chemical activity going on inside. They're like a metropolis because they're crowded and busy and full of interactions, and they seem chaotic but they've got their own structure. But really, cells are so much more intense than any city or factory you’ve ever seen. Like, first of all, there's no up or down inside a cell. Gravity barely matters. Every tiny bit of space is fully utilized. Activity is everywhere, and electric currents are constantly flowing. You might not think of yourself as carrying much of an electrical charge, but you are. The food you eat and the oxygen you breathe are converted into electricity inside your cells. So, why don’t we knock each other over when we touch, or, like, set the sofa on fire when we sit down? Well, it’s because all this is happening on such a small scale. The voltages are only, like, a tenth of a volt, and they’re only traveling nanometers. But if you scaled it up, the impact would be equivalent to, like, 20 million volts per meter. As much as the core of a lightning bolt.
No matter what their shape or size, all your cells are basically built the same way. They all have an outer shell, the cell membrane. They all have a nucleus, which stores the genetic information they need to function properly. And between the two, there's this bustling space called the cytoplasm. The cell membrane isn’t this tough, rubbery thing that you could poke a pin through, it's actually made of fatty substances called lipids, which are kinda like light machine oil. At a molecular level, water becomes this heavy gel, and lipids are practically like steel.
If you could, like, visit a cell, you probably wouldn't like it very much. If you blew up atoms to the size of peas, a cell would be this sphere, like, half a mile across, held together by this complex scaffolding of beams and girders called the cytoskeleton. And inside, millions and millions of objects. Some as big as basketballs, others as big as cars, all zooming around like bullets. You'd barely be able to find a place to stand. And you'd be bombarded from all sides, thousands of times a second. Even for the members that live in a cell, it’s a dangerous place. On average, every strand of DNA gets attacked or damaged – smashed or torn apart – every 8.4 seconds. That's, like, 10,000 times a day. And all those injuries have to be fixed pretty quickly, or the cell won’t survive.
Proteins are super active. They’re always spinning and jiggling and flying around, and they bump into each other a billion times a second. Enzymes, which are themselves a type of protein, they zip around doing their thing. They complete, like, a thousand tasks every second, constantly building and rebuilding molecules. Adding a piece here, taking one off there. Some enzymes are constantly monitoring the proteins passing by, and they mark the ones that are damaged, or defective. Then those marked proteins get taken to these structures called proteasomes, where they get broken down and turned into new proteins. Some proteins only last for half an hour. Others last for weeks. But they’re all living these incredibly frantic lives. As one person put it, "everything inside a molecule is moving at an incredible speed. We can barely imagine it."
But if you slowed things down, just enough to see how everything interacts, it wouldn't seem quite so overwhelming. You'd see a cell as just millions of objects – lysosomes, endosomes, ribosomes, ligands, peroxisomes, proteins – all of different sizes and shapes, bumping into millions of other individual objects to perform the most routine tasks. Getting energy from nutrients, assembling new structures, getting rid of waste, fighting off invaders, sending messages, and doing repairs. A typical cell contains about 20,000 different types of proteins, and at least 50,000 molecules of about 2,000 of those proteins. So, if you're just counting the molecules with at least 50,000 of each type, there are, like, a hundred million protein molecules in every cell. Which is a crazy number!
All this activity takes a huge amount of energy. Your heart has to pump about 90 gallons of blood every hour, about 2,000 gallons every day, and, you know, almost a million gallons per year. That's enough to fill a few Olympic-sized swimming pools to keep all your cells supplied with fresh oxygen. That’s when you’re resting. When you’re doing any strenuous activity, this increases. That oxygen is taken in by the mitochondria, the power plants of the cell. A typical cell has about a thousand of these, but it varies depending on what the cell is doing and how much energy it needs.
Mitochondria used to be captured bacteria. They have their own genetic instructions, divide on their own schedule, and even speak their own language. They're essentially tiny guests living inside our cells. Why’s that good? Well, because almost all the food and oxygen you take in gets processed and sent to the mitochondria. Then they convert it into a molecule called adenosine triphosphate, or ATP.
You may not have heard of ATP, but it's basically what keeps your body running. ATP molecules are tiny batteries. They move around inside the cell, providing all the energy for cellular activity, which is how you get everything done. At any given moment, there are usually a billion ATP molecules inside every cell in your body, and their energy is depleted after about two minutes. Then a billion new ATP molecules take their place. Every day, you produce and consume about half your weight in ATP. Feel that warmth in your skin? That's your ATP at work.
When cells aren't needed anymore, they die in this dignified way. They take down all the pillars and arches that hold them up. Then they quietly digest their components. This process is called apoptosis, or programmed cell death. Billions of cells die for you every single day, and billions of other cells clean up after them. Cells can also die violently, like when you get an infection. But most of the time, they just die when they're told to. In fact, if they don’t get a command to keep living – like if they don’t receive the appropriate signals from other cells, they’ll just kill themselves. Cells are needy.
Sometimes, when a cell doesn’t die when it's supposed to, it starts dividing and spreading like crazy. That's what we call cancer. Cancer cells are basically just cells that have lost their way. Cells make these kinds of mistakes all the time. But our bodies have this amazing system for fixing those mistakes, that stops the cellular activity from spiraling out of control. By average, people get a deadly disease once for every quadrillion cell divisions. Cancer is largely a case of just incredibly bad luck.
The amazing thing about cells isn't that things occasionally go wrong, but that they keep everything running smoothly for decades. To do that, they’re constantly sending and monitoring messages from all parts of the body: instructions, questions, corrections, rescue calls, updates, notifications to divide or die. Most of these messages are transmitted by chemicals called hormones, like insulin, adrenaline, thyroxine, and testosterone. Some messages are transmitted from the brain or regional centers. That’s called paracrine signaling. Finally, cells just communicate directly with their neighbors to make sure they’re all on the same page.
The thing to remember is that cells are in a state of constant, frenetic, aimless motion and collision, driven by nothing more than the basic laws of attraction and repulsion. The motion of any individual cell is, in fact, utterly random. All the motion happens smoothly, repeatedly, reliably, so we barely even notice it. Yet, it all not only keeps the cell in good order, but it also keeps us in perfect harmony. Trillions and trillions of reflexive chemical reactions, in ways that we’re only just beginning to understand, add up to create you. Don’t forget, every living thing is a miracle of atomic engineering.
Some organisms have cellular organization that makes ours look sloppy and amateurish. If you break up the cells of a sponge (for instance, by running them through a filter) and pour them into a solution, they’ll quickly reassemble themselves into a sponge. You can do this over and over, and they'll always stubbornly come back together. That’s because, just like you and me, and everything else, they have this powerful drive: the drive to keep on living.
And all of this is thanks to this incredibly strange, unwavering, and, frankly, very poorly understood molecule. A molecule that isn't alive itself, and that mostly just sits there doing absolutely nothing. It's called DNA.