Unit 2 - Cell Structure & Support

Unknown Speaker

Hey everyone, welcome back to Biggie Bio! I'm Chloe, and I'm here with Grady—who, by the way, tried to convince my students last week that mitochondria were invented in Iowa. That’s not even how evolution works, Grady.

Grady Killpack

Hah! Okay, but can you prove me wrong? Joking, joking… Sort of. But really, today we’re diving deeper inside the cell. Last episode, we broke down water’s properties and the chemistry of life—this time it’s all about the nuts and bolts that make up every cell. Ya ready, Chloe?

Unknown Speaker

Born ready. So, let’s start with the basics. All living things are made of cells, right? But there are actually two main types: prokaryotes and eukaryotes. Biggest difference? Where that precious DNA lives and how fancy the insides are. Prokaryotes, that’s your bacteria and archaea, keep DNA in this open region called the nucleoid. No true nucleus. Tiny, but mighty!

Grady Killpack

And eukaryotes—think plants, animals, fungi, and protists—pack their DNA inside a nucleus, which is surrounded by its own membrane. Eukaryotes’ve also got these specialized, membrane-bound organelles. It’s like having tiny rooms for each job in the cell… kind of like your legendary craft room, Chloe.

Unknown Speaker

Oh, that’s such a good comparison. Okay, random story time: One year, I set up different stations in my classroom—one for cutting, one for painting, one for glitter. It saved my sanity, honestly. Because if you let everything happen in one spot? Boom! Chaos. Glitter everywhere, even in the janitor’s eyebrows. But when you give each activity its own space, everyone’s more productive and nothing explodes. That’s exactly what compartmentalization does in cells—organelles separate out different reactions so nothing interferes. Efficiency central!

Grady Killpack

Which also means, just like you keeping the glitter away from the paint, cells are keeping, say, protein-building in the rough ER, and energy production in mitochondria. Not all mixed together, or you’d get chemical mayhem. So, in summary: Prokaryotes? Simpler, one big open floor plan. Eukaryotes? Compartmentalized—open-concept, but with at least a couple soundproof doors.

Unknown Speaker

And that makes all those complex life processes possible! Let’s keep this party rolling—because those organelles didn’t evolve overnight. There’s an origin story, and it’s wild...

Grady Killpack

Ah, yes—the endosymbiont theory. This one’s basically a sci-fi origin story, but it’s real. Imagine an early eukaryotic cell just... eating a prokaryote, and then instead of digesting it, they start living together. Mutual benefit: the classic roommate situation, but less arguing about dirty dishes.

Unknown Speaker

Right, and the main supporting evidence? Both mitochondria and chloroplasts actually have double membranes, their own circular DNA, and ribosomes. That’s super similar to what you see in prokaryotes. And they’re technically self-sufficient enough to do their own thing, although you’ll never spot a mitochondrion running around free in the wild.

Grady Killpack

If only, right? Just wild mitochondria sprinting through the fields of Iowa. But really—the double membrane comes from the engulfing process, the DNA and ribosomes are like souvenirs from their ancient prokaryote ancestors. All signs point to “yeah, this merger happened.” Now, mitochondria are the official energy site—cellular respiration HQ. Their inner membrane has these folds called cristae, which crank up surface area for ATP production.

Unknown Speaker

And the number of mitochondria? Totally depends on a cell’s energy needs. Muscle cells, especially marathoner muscles, are just packed. That’s why when you’re burning through energy—running, wrestling, or just wrestling with the printer at work—mitochondria are working overtime.

Grady Killpack

All right, Chloe, the eternal debate: Mitochondria or chloroplasts—which is cooler?

Unknown Speaker

Tough, but I’ve got to say chloroplasts. Only photosynthetic organisms get ‘em! That’s pretty exclusive. They turn sunlight into chemical energy, they’re why plants are green—thanks, chlorophyll! And inside, they’ve got stacks of thylakoids (scientific pancake towers, basically) for the light reactions. So... yeah, it’s pretty magical.

Unknown Speaker

So, picture this: Every cell needs a support system—something to anchor organelles, help things move around, and keep the cell from flopping like an overcooked noodle. That’s the cytoskeleton’s job. It’s a network of fibers running through the cytoplasm, almost like scaffolding in a building.

Grady Killpack

Three main types: microtubules, microfilaments, and intermediate filaments. Microtubules are these hollow rods made of tubulin protein—they’re like train tracks for organelles, guiding things with the help of motor proteins. Also huge for moving chromosomes during cell division and making those classic cell appendages: cilia and flagella.

Unknown Speaker

Microfilaments are solid rods, made out of actin. They help the cell hold its shape—plus, actin teams up with myosin to make muscles contract. If you’ve ever had a muscle cramp, you can blame actin and myosin for working a little too well together. And microfilaments even help divide animal cells by making that contractile ring during mitosis—like, literally pinching the cell in two.

Grady Killpack

Intermediate filaments? These guys are the underappreciated structural workhorses. They last longer, act like anchors for the nucleus, keep organelles in place, and form the nuclear lamina—the inner lining of the nuclear envelope. So if a cell starts to lose its shape or things get out of place, usually some intermediate filaments are involved. By the way, sickle-cell anemia is a good example of what happens when cytoskeletal support goes wrong—the abnormal shape of red blood cells is due in part to disrupted cytoskeleton function.

Unknown Speaker

And, I gotta say, I love a good hands-on model. Grady, didn’t you once use tumbleweeds and string to show off the cytoskeleton in your class?