Cells. No matter how bad you think you are at biology, you’ve almost definitely heard of cells. These are one of the most fundamental units in biology, but they can also prove to be some of the most complicated things that the universe has to offer. They’ve got dozens of different organelles that many of you reading probably have never heard of: there’s peroxisomes, there’s nucleoli, there’s COPI Vesicles…
But it doesn’t have to be this way. Cells might be extraordinarily difficult to understand, but they can also be relatable to things in your lives. Just like with our Biomolecules Personality Test, you might find that cells are actually quite familiar… maybe they’re quite comparable to your home.
While not as small as the biomolecules mentioned, the parts of a cell are still undoubtedly small, yet extraordinarily complex. From the “powerhouse of the cell” to the organelle that stores genetic information, each organelle plays a key role in a cell’s biological function, helping it grow, prosper, and survive.
Organelle #1: Cell Membrane/ Cell Wall
Our first cell component is the Cell Membrane, which is a word you’ve probably never heard of before, but it’s far simpler than you think. Picture this: you’re sleeping in your house in the middle of the night, and you hear a BANG. When you wake up frantically and look out the window, there’s an intruder about to enter your house. They hold a host of weaponry, from explosives to firearms, yet they don’t seem to be coming in. Or rather… they can’t…?
That’s right, you know for a fact that they can’t get into your house. Why? Because your house is equipped to protect you from the dangers of outsiders. First off, the entire house is made of walls—walls that keep anybody unwanted from getting out. And they shouldn’t be thinking of trying to break in through the doors either, because your house is also equipped with a security system that will stop any unwanted intruder from getting into your home. You’ll only have people coming in if you want to… if you select them.
That’s the basic idea of the cell wall and the cell membrane. In a home, it takes the form of a wall and security system. The Cell Wall acts as both a source of structure for a cell and a barrier that keeps unwanted material out, like the walls of a house that keep out dirt and debris. The plasma membrane helps regulate what goes in and out directly, similar to how a security system keeps out invaders by identifying them and protecting you. This idea of being selective about what can go in and out is called Selective Permeability, and it allows certain molecules, such as Oxygen and Water, to enter while keeping toxic chemicals out of your body. Within the cell membrane is a vast array of biomolecules (check out our biomolecules personality test article!) collectively referred to as the Fluid Mosaic Model, and each has a host of mechanisms the cell can use to move materials inside and outside itself.
Organelle #2: Cytosol/Cytoplasm
. Now, the house isn’t just composed of walls or a security system, is it? No, of course not. A house is also made of primarily empty space. Just like atoms. Or my bank account. In each of the house’s rooms, you can move freely through them as long as you watch you step because in most rooms there are things you might crash into; furniture, electronics, and items that represent the cell’s materials in this metaphor.
Each cell has a lot of empty space like this which is called the “cytosol”. It’s a jelly-like substance that houses all the organelles, giving the cell shape.
But just like houses, cells aren’t just this singular, big mass of unified space. Houses are divided into smaller parts, each with their own purpose; there’s the bedroom, the bathroom, the kitchen, living room and the closet…
Cells are just like that. They have a diverse range of processes that need to be done, just like how humans who live in a house need to pee, cook, and work. As a result, cells have distinct compartments, each with an environment suited to the function it performs within the cell. They’ve got completely different and distinguished conditions… specific pHs, specific temperatures, pressures, so on and so forth. And of course, they each have different functions, performing unique jobs for the cell.
Organelle #3: Cytoskeleton
Another important question to ask when building a house: Is it sturdy? Can it support itself? Is it stable? It’s not only a question asked when building tall buildings. It’s also integral to a cell, and the answer to that is an organelle known as the cytoskeleton. The cytoskeleton is a vast network of proteins throughout the cell that helps keep it sturdy.
The cytoskeleton is composed of microtubules and filaments, all of which resist compressive and tensile forces exerted on the cell. These things are made of proteins and are present within the cell’s cytoplasm.
And these structures aren’t just inside the cell. They also exist outside; some cells have tails called flagella, or hairs called Cilia that can help cells communicate with one another, all of which are made of microtubules. In a cell-house, this could be the equivalent of the doors, windows, or any other feature visible from the outside of the house. The cytoskeleton provides structure to the cell both inside and out.
Organelle #4: Nucleus
You’ve probably heard of this organelle before… the Nucleus. Even if you don’t know much about it, you certainly have heard of it. It plays a major role in all cellular activities.
But what does that look like in a house? One thing in a home that could resemble a nucleus could be the safe – a safe is one of the most important parts of a house, right? It’s got all sorts of important things that your house and you need to keep safe: your social security number, your passwords, your Google search history… okay, maybe that last one just applies to me. In the nucleus, there’s one crucial thing that needs to be kept safe: your DNA. You remember how, in the Biomolecules personality test, we mentioned that DNA is the blueprint for creating proteins and for keeping your genes regulated and expressed in your body.
But what if someone just grabbed your safe and smashed it on the floor? Well, if it didn’t have a strong foundation, then that would mean trouble because all of your private and sensitive information would be exposed all the way to the outside world. A more robust safe, however, would be able to keep everything secure and protect all your belongings. In a cell, this could be sort of like what many people refer to as the Nuclear Lamina; it’s a network of filaments called “Intermediate Filaments” that keep the nucleus stable and strong (see the cytoskeleton section if you forgot already), protecting the DNA and giving it that robust aspect.
But just like anime and alcoholism, the Nucleus might not be for everyone. Not every organism on Earth has a nucleus— these kinds of organisms are called prokaryotes. This doesn’t necessarily mean they don’t have DNA; they still do, but it’s not as well protected as your nucleus.
Organelle #5: Lysosome
Here’s another thing to think about in biology: waste. Cells have a lot of trash inside of them– with all those organelles and functions occurring inside, it’s hard not to be filled with a lot of unnecessary molecules that are largely unneeded. Proteins just doing their jobs might undergo a small structural change that destroys their ability to catalyze reactions. Maybe another nearby cell has been destroyed, and there’s a lot of debris that needs to be cleared (see Apoptosis). And in your home… What do you do when there’s a lot of trash on the ground, most of it really nasty-looking, and pretty much purposeless to you and your life?
You throw it in a trash can, of course! (What else were you thinking of?) Well, cells also have quite a few of those around, and they’re meant to take waste down and digest it.
Organelle #6: Chloroplast
Many cellular processes require energy, but where do they get that energy from? While your first thought might be about the food they eat, many organisms also use a different kind of energy… That’s right, it’s light energy, which is collected by the organelle known as the chloroplast. The chloroplast is an organelle that harvests energy in the sun via its thylakoid membranes.
In relation to the house metaphor, think of it as the solar panels that help provide energy to keep your house functioning. They take the useless light energy and turn it into something useful, either storing it in a battery or delivering it directly to one of your outlets, so you can get through all the tasks you need to do during the day.
This parallels what chloroplasts do in plants and some other species. It uses light energy to split water, makes a bit of ATP (think of it like a battery), and helps create NADPH, another battery-like molecule. The final product occurs in the chloroplast’s intracellular space, producing glucose, a sugar molecule with a ring-like structure. The photosynthetic process is quite complicated, but just know that it takes place in the chloroplast, the cell’s miniature solar panels.
Organelle #7: Mitochondria
Glucose itself stores energy, but there’s a bit more to the energy of a cell. Even once you get glucose, there’s still another process that needs to be done to turn that energy into something the cell can actually use. This process, known as cellular respiration, converts the energy stored in glucose into a form that is useful. It’s got a whole bunch of complicated steps… glycolysis, hexokinase, DHAP, pyruvate, malate, blah, blah, blah, (maybe in a future article), but what you really need to know here is that most of the process occurs in the Mitochondria.
So what’s that like in a house? Well, mitochondria are kind of like the power cords and electronic devices; they take all that energy from the sun (or in some cases, the power plant) and turn it into a product that you’ll actually care about. They power everything, from your TV to the oven to my laptop’s search history— oops… ignore that last one—nothing to see there. The final product of the energy that the cell actually uses for all its day-to-day activities is called a molecule of ATP, which stands for adenosine triphosphate. You probably notice that “tri” in the “triphosphate” has a resemblance to the number three. And that’s true; ATP is sort of like a battery pack with three batteries. There are these three “phosphate groups” that exist in every ATP molecule, and energy is released and used in cell activities whenever one of the phosphate groups is taken off the ATP molecule, leaving two more phosphate groups, which is called ADP, which stores less energy. This is kind of like taking three batteries out of a battery pack. You have three units of energy when the packet is full, and when one of the phosphate groups (a battery) is removed, you can add. If another phosphate group is taken off, it’s called AMP. To “charge” the battery, these phosphate groups can be re-added to create ATP, which is what the mitochondria essentially do. Whenever energy is needed for something, the cell uses ATP in almost every circumstance, as the most energy can be extracted from it.
Organelle #8: Vesicle
You’re probably thinking after all this reading: Wow. That’s a lot of metaphors for each organelle. Yet you may still be wondering: Where does the vesicle fit into this? Well, there’s a lot of stuff that needs to be organized for the cell to be functioning; you need to move different enzymes, components needed for hundreds of different types of chemical reactions, and so much more. That’s the role of the vesicle; it’s a little sac (many of which) that is spread around the cell, containing all the materials needed for the cell to go about its business.
In a house, you can think of this as a storage room; I’ve got quite a few of these in my home as well, and I’m sure you do too. Just think of those closets scattered around your home filled with all sorts of things, from old devices, books, expired candy bars (wait, I think that’s only for my house).
This is not really an organelle, but Apoptosis
While not really an organelle, we should definitely mention a key biological process. It occurs in your body daily and involves cellular death. Sounds pretty intimidating, right? Don’t fret, though, this isn’t a bad thing. It’s actually quite necessary and useful for your body. What process are we talking about? Well… It’s apoptosis! Apoptosis is a programmed cell death that usually occurs when a cell is damaged or abnormal. Often, it helps kill cancer cells before they become a threat and helps regulate the cell population to make sure there aren’t too many cells in one spot.
Conclusion
Cells are highly complex in the universe, with a vast field of study that goes far beyond what this article could cover. Regardless, we do hope that you learned a lot more about the parts of the cell, from the lysosome, to the mitochondria to even the nucleus. These metaphors may have helped simplify them to you, but keep in mind that they can still be quite complex when you take a deeper look.
FURTHER READING SECTION COMING SOON: