Unit 3 - Enzymes & Energy

Unknown Speaker

Hey y’all, welcome back to Biggie Bio! Chloe here, and I’m joined as always by my partner-in-cellular-crime, Grady. So today we’re rolling right from our cell structure and membrane talks into the world of metabolism—kind of like that shift at a wrestling tournament, y’know, where suddenly it’s time to feed a busload of hungry teenagers and you wonder if the snacks you prepped will last until round five!

Grady Killpack

Ha! And Chloe’s right, I’ve seen her table of snacks—like an anabolic pathway in action: building, building, and then, whoosh, wrestling team shows up and it’s catabolic chaos, everything getting broken down! Metabolism in a nutshell is just all those chemical reactions going on in your body, right?

Unknown Speaker

Exactly, Grady. Metabolic pathways can go two directions: anabolic, which need energy to build complex molecules—think making proteins from amino acids or making snacks from groceries!—and catabolic, which break things down and release energy, like digesting all those snacks and getting energy out.

Grady Killpack

That’s the core. And it’s wild how much of this is about energy, which, I mean, at the end of the day, is the ability to do work. Cells need constant energy flow. Lose that? No more cellular order—and, well, the end’s not pretty.

Unknown Speaker

Pretty grim. But it ties back to something we touched on in our last episode about homeostasis: cells are always fighting to keep order, but they don’t break physics doing it. The first law of thermodynamics says energy can’t be created or destroyed, just converted. So that chemical energy in your food becomes kinetic—like, wrestling flips or lifting boxes—and some gets released as heat, always.

Grady Killpack

Yeah, and here’s where the second law jumps in. Every time energy changes forms, a little’s lost as heat—so the universe’s entropy, or disorder, always increases. Students get tripped up thinking cells are breaking the law by being so organized, but actually, as long as the overall entropy in the universe is up, cells are in the clear. We burn glucose, we release CO₂ and H₂O, and the heat that escapes is all about cranking up that entropy.

Unknown Speaker

And real talk, that’s why life needs a constant energy input—like, if your energy output ever exceeds input, things start to fall apart. That’s when death happens. Gosh, this is getting dark for an AP Bio review, huh?

Grady Killpack

Seriously, but it’s true! And the key idea here is ‘free energy’—Gibbs Free Energy, or ΔG. It helps you tell if a reaction’s gonna go on its own or not. Exergonic reactions, ΔG’s negative, energy comes out—like respiration. Endergonic, ΔG positive, you gotta put energy in, like photosynthesis.

Unknown Speaker

It’s like… okay, Grady’s trademark analogy—

Grady Killpack

Uh oh, here we go—beef jerky marathon time. So, you’re running a marathon: your body breaks down glucose, releases usable energy, and some is lost as heat, just like munching on beef jerky for fuel. You can only keep running as long as you keep getting more energy in than you lose sweating it out—and that’s exactly how cells survive, too!

Unknown Speaker

Love that. Should we move on to talk about how cells actually cash in on this energy—like, what’s their version of that ultimate snack for running all their work?

Grady Killpack

Let’s do it. ATP—adenosine triphosphate—is like the ultimate school pep rally battery. Structure-wise, it’s got this adenine, ribose, and a tail with three phosphates. The magic happens when you snap that third phosphate off in a hydrolysis reaction—boom, energy’s released, cell’s ready to get to work.

Unknown Speaker

And it’s not just about having a stack of ATPs lying around—cells are constantly breaking ATP down and rebuilding it from ADP plus a phosphate. I always picture it like, you know, keeping the gym lights blazing for the pep rally all night—you’ve gotta keep recharging! It’s a cycle. Energy from exergonic reactions, like respiration, powers the ATP rebuild, and then ATP fuels all the stuff in the cell that needs energy.

Grady Killpack

Yeah, and ATP doesn’t work alone. It couples up exergonic and endergonic reactions. So let’s say your cell needs to build some big molecule—anabolic reaction, energy required! The energy comes from ATP getting hydrolyzed, and the released phosphate can even stick onto that other molecule—phosphorylation—making it more reactive. Kind of like passing the energy baton down the line.

Unknown Speaker

And just like the pep rally, there’s different jobs happening. Cells do mechanical work—moving stuff, like muscle contraction or cheer jumps, heyyy. Then there’s transport work—pumping ions across membranes against the gradient, which we covered last episode. And finally, chemical work—making stuff: building polymers, synthesizing DNA, you name it. All roads lead to ATP as the energy source.

Grady Killpack

Since we’re talking quizzes, classic ATP question right here: What’s ATP’s primary job in the cell? To act as the main energy currency. Students mix this up with, like, transport or storage, but really, ATP’s just the quick cash—you spend it instantly, you don’t stash it away.

Grady Killpack

Absolutely. Enzymes—these are your cell’s ultimate catalysts. They’re proteins, and their job is to speed up reactions by lowering the activation energy—the little ‘push’ needed to get a reaction started. Without them, some reactions would take years, or, like we saw in that potato catalase experiment from the quiz, even a thousand years! Instead, enzymes get it done in milliseconds. Wild, right?

Unknown Speaker

It’s all about the active site. Picture a lock-and-key, but really, it’s more like ‘induced fit’—the enzyme changes shape to cradle the substrate. That’s where it either breaks stuff apart (catabolism) or builds things up (anabolism). The enzyme itself isn’t changed or used up in the process, so it can keep doing its thing over and over.

Grady Killpack

But—here’s the catch—enzymes are picky. Temperature, pH, and substrate concentration all affect how well they work. Too hot? They denature. Too acidic or basic? Also denature. Like, remember my ‘fried egg in the science lab’ demo? I cranked the Bunsen burner, and—boom—egg turns solid white because those proteins denature, just like enzymes in your cells if you spike a fever too high. Temporary fever can help fight infections, but a long-term fever will mess up enzyme function fast.

Unknown Speaker

And that’s huge for stuff like lactose intolerance: if you don’t make the enzyme lactase, you can’t break down lactose, so you get all the classic symptoms. Enter Lactaid supplements—they give you the missing enzyme so you can digest the dairy like everyone else. Seriously, enzyme structure equals enzyme function. One gene mutation and bam, your system’s out of whack.

Grady Killpack

Now, enzyme regulation is a world unto itself. You’ve got competitive inhibitors, like Relenza for the flu—those block the active site so the actual substrate can’t bind. Then you’ve got noncompetitive and allosteric inhibitors, which bind somewhere else and change the enzyme’s shape so the active site isn’t even the right shape anymore. Feedback inhibition’s another—where the end product of a pathway turns around and says, “Whoa, slow down!” by blocking the first enzyme in the chain. Keeps metabolism in check.