A Beginner’s Guide To Biology. Volume One: The Cell.

High school science class on steroids.

Aaryan Harshith
9 min readMar 16, 2021

This is a cell. It’s the smallest thing you could consider alive:

It’s really, really, really tiny.

And…that’s about where most people’s knowledge of cells ends. Unfortunately, biology doesn’t let people get away with that Google-level answer. If we’re going to start anywhere, it might as well be here. Enter the world of the cell.

For starters, cells aren’t what they seem. They actually come in two flavours: chocolate and vanilla. Sorry, I was eating some ice cream there. Cells come in two flavours: prokaryotic and eukaryotic.


Here’s a eukaryotic cell:

You might not be able to tell unless we get a side-by-side comparison going on, but eukaryotic cells are about 10X bigger than their prokaryotic friends. They’re huge.

Another part of what makes eukaryotic cells so unique is how they tuck their DNA (genetic information) into a safe little blob called the nucleus. Eukaryote is Greek word that means “true kernel”— hinting at how these cells separate their nucleus from everything else inside them. Eukaryotic cells also have specialized cleanup crews called lysosomes, plus a lot of other high-end amenities built into them.

Oh, and there’s one last distinction. Eukaryotes evolved to be able to interact in groups and specialize for different functions. That teamwork let them build multicellular organisms like us, along with basically every other plant and animal around.


Here’s a prokaryotic cell:

Someone’s getting a little insecure, aren’t they?

Prokaryotes are smaller than eukaryotes and have free floating DNA. They’re also a lot simpler, with much fewer components (also called organelles). But to make up for that, they come with these rad looking tail-thingies called flagella so they can move around. Totally worth it.

But most importantly, prokaryotes can’t work together and have their own roles. They’re too basic. Instead of millions of them combining to create a rabbit, or a tree, or a narwhale, a prokaryote is the organism. Think of bacteria, algae, and those things that float around in your eyes.

For now though, let’s go deeper into what matters to us — eukaryotes.
Let’s pay our old friend a quick visit again and explore the places where all the action happens:

I’ve named this cell Marty. You see the big red blob smack dab in the middle of Marty? That’s his nucleus.

In biology, there’s no way you can have a conversation about cells without bringing up their nucleus at least four times. Why? Because our cells’ nuclei are the world’s greatest safes. It’s their job to protect DNA — the magical molecule that makes us who we are.

What’s DNA? To understand that, let’s take a quick detour into proteins.


Wait, what did I just say? Proteins?

Yeah, proteins. They’re probably the most misunderstood concept in biology. Most people think they know everything about them, but there’s a good chance their knowledge doesn’t extend further than weightlifting and chicken wings. Seeing proteins just for what they do in our muscles is a disgrace, so it’s time to level up:

No amino acids were harmed during the production of this article.

“A protein’s just a long chain of special molecules called amino acids. Just like lego bricks, you can snap together different amino acids in different orders to get an infinite number of proteins.”

Some common nicknames for proteins are:

Peptide: Just a small protein. Definitions vary, but they usually count as any protein with less than 20 amino acids forming it.

Enzyme: Proteins built specifically to make chemical reactions happen. For example, an enzyme called Alpha-Reductase converts testosterone (also a protein) into a more potent variant called DHT. Not-so-fun-fact: Too much DHT shrinks our hair follicles, and hyper-active DHT enzymes are exactly why you see guys balding in their fourties.

Fibrous Proteins: Speaking of hair, you can thank (or blame), a protein called keratin for the colour, shape, and quality of your hair, skin, and nails.

Immunoglobulin: Ever heard of an antibody? Our immune cells manufacture these proteins to mesh like a jigsaw piece with the receptors on foreign substances. They physically prevent bacteria and viruses from binding to other cells and mark them as targets to be killed.

There’s exactly 141,578.6 more things a protein can do. Without them, we’d be very dead, and as we all know, dying isn’t very good for your health. Thanks, proteins!


Anyway, back to DNA.

DNA’s a long, friendly molecule in our cells’ nucleus that looks like a twisted ladder. It tells our cells how to make proteins. The rungs of this ladder are what we call “base pairs”, and they make us tick:

A common analogy for base pairs compares them to a blueprint, but there’s a better way to see it:

Take coding, for example. When a software engineer writes a program, they’re using digital instructions to get a computer to do something.

Think of DNA as the code our bodies are supposed to run — just written in the language of chemicals. If we simplify DNA to a chemical paragraph, our cells “read” that paragraph in groups of three base pairs at a time. We call these chemical words of information codons.

Every codon corresponds to its own amino acid. As cells scan along the length of DNA’s rungs, the codons spell out the type and order of amino acids they need to make certain proteins. The segments of your DNA that code for entire proteins are called genes. They’re the things that turn you into an X-Man (or woman) if you jump into your local pool of toxic waste.

Disclaimer: Please don’t do that.

Did you know that every one of our cells has about two metres of genetic information packed into it? You’d only need a sugar cube’s worth of cells to store an entire internet’s worth information on. If you’re wondering why we don’t do that already, that’s because you’d be left with a literal sloppy disk.

But if DNA’s just the program, who runs it?


Meet the ribosome — it’s your cell’s construction worker.

He’s actually dyslexic and has no idea what he’s doing.

Before our DNA’s ready to be read by “experts” like the ribosome, it needs to get ready. To prepare, an enzyme (remember what that is?) copies our DNA and splits it into bite-sized pieces to send over for fabrication. These bite-sized pieces are better known as messenger RNA, or mRNA.

Ribosomes read that mRNA as instructions, grab the amino acids floating around them, and get to work by smushing them together — slowly building out a chain. After reading a codon that signals the end of a gene, the ribosome snips off the end of its amino acid string. You’re left with protein à la carte — worthy of a chef’s kiss.

But wait, let’s step back. Does mRNA sound familiar? Well, it should, since someone’s probably going to be injecting the stuff into you soon.

mRNA’s how Moderna’s COVID-19 vaccine works. The vaccine contains the mRNA instructions that your ribosomes need to produce the proteins on the ‘rona’s surface. It gives you all the punch of the real thing — without the risk of accidentally sick. Just another day at the job for ribosomes.

And that’s not even the start of it.


And then there’s the lysosome.

In high school, you might’ve learned that lysosomes are the parts of your cells that munch on things that they don’t need anymore. Their insides are so acidic that they can disintegrate everything from proteins that didn’t come out well to bacteria, poison, and allergens. Best job ever.


Finally, let’s make a stop to meet an interesting character.

This is the mitochondria. It’s a tiny bean-shaped organelle with a huge sweet tooth. Our mitochondria convert glucose from the food we eat and oxygen from the air we breathe into a molecule Adenosine Triphosphate (or ATP). Our cells break the chemical bonds in ATP to get power, and just like money, they can spend it to move around, multiply, and do other normal cell things:

Wow, it almost looked kinda cute for a second…

We call this process of creating and breaking down substances for energy metabolism. It isn’t the same kind that decides how fast your can burn off a burger, but it is the kind that decides how quickly your muscles start burning in a workout.

Don’t be quick to jump to conclusions, though. Just because someone doesn’t like working doesn’t mean they’ve got messed up mitochondria. They might be suffering from a serious disease called laziness. Contact your doctor today.

Side-note: Not all mitochondria are created equal Mitochondria actually have DNA of their own, and you get all your mitochondrial DNA from your mother. Now you know where your athletic prowess (or lack thereof) comes from.

There’s More…

And we’re just viewing the body at a micro-scale. Let’s zoom out.

One cell is, well…a cell. Going up a few levels in complexity gives us tissue. The word “tissue” comes from the French word “tisse”, which means “to weave”. If you saw what scientists saw when they looked under the first microscopes, that name wouldn’t be surprising:

Rabbits multiply quickly? You’ve just never seen cells.

When millions of the same cells intertwine and build onto each other, you get tissues. It’s simple, really. What do you call a group of fish? A school. What do you call a group of people? A community. What do you call a group of moose?Mooses? Meese? Mice?

Alright, let’s not go there today.

But here’s the good news — this is one of the few times biology isn’t complicated. What do you call a group of muscle cells? Muscle tissue. What do you call a group of skin cells? Skin tissue. What do you call a group of nerve cells? Nerve tissue. If you can’t see the pattern here, then there might be something wrong with your brain tissue.

Tissue isn’t the end of it, though. Groups of specialized tissue create organs. You know, like your heart or liver or lungs? Things are starting to look a lot more familiar now, aren’t they?

But you wouldn’t believe how many people assume, for example, that your gut’s just made of …intestine cells. That’s not how it works . Your gut’s an organ, so it’s made of dozens of types of tissues with millions of cells. I’m talking about everything from muscles to veins to nerves to glands — all in one part of your entire body.

But that’s for another week where my wrists aren’t killing me from typing. As for you, there’s probably a lot left to think about. Till then, look forward to another adventure, where we venture beyond cells with pancakes, skyscrapers, and infinite voids. That’s all for today biology class.

Peace out,
(self-proclaimed cool science teacher)