Fall2025-week03-From Bonds to Biomolecules

Eric Marquette

Hey folks, welcome back to another BIO 110 Recap! I’m Eric, your friendly neighborhood podcast nerd, and as always I’ve got the brilliant Avery Lin here with me. Avery, you ready for chemistry boot camp?

Avery Lin

As ready as I’ll ever be! Look, I’ll be totally honest—I just about flunked chemistry in high school, so if I get this stuff, anyone can. Let’s do it. So, Eric, where are we starting today?

Eric Marquette

We’re zooming back to basics—atomic structure. And it’s wild how much biology relies on just a few building blocks. You remember those three atom parts, right? Protons, neutrons, electrons? Protons are positive, neutrons are the neutral ones, both are in the nucleus, and electrons zip around the outside.

Avery Lin

Yeah! Electrons are those little guys out on the edge that cause all the fuss. Especially the valence electrons, which, if you’re like me and immediately forget jargon, just means the ones in the outermost shell—they’re the ones that really want to get cozy with other atoms.

Eric Marquette

Totally. And it turns out, how many valence electrons an atom has, totally determines how it bonds. Carbon is the star of biology—four valence electrons, so it can make four bonds, north, south, east, west... It’s like atomic speed dating, but everyone’s looking to be “full”. Hydrogen just needs two electrons and is happy with one buddy. Oxygen wants eight and has six valence electrons, so it can make two bonds. Simple, right? Except, not really. The way these electrons get shared or transferred is where it gets fun.

Avery Lin

Right, and that’s where the bond types come in. There’s covalent bonds, which are all about sharing—like if we both have snacks at the movies and we split. Except, sometimes one person hogs more popcorn—that’s a polar covalent bond. Nonpolar is when the sharing is fair. Then, ionic bonds are where one atom just gives up the snack, so now one is positive and one is negative and they’re basically glued together by attraction. And then there’s hydrogen bonds, which... okay, those always confused me. They seem "weak," but so important?

Eric Marquette

Yeah, hydrogen bonds are a bit quirky. They aren’t about hydrogen “bonding” to something, it’s not like glue, it’s more like a friendly handshake between molecules that already have polar ends—think water molecules. They're weak alone but mighty in numbers, and that’s part of what makes water so weird and so vital. But we’ll get to water in a bit. Any questions so far, Avery?

Avery Lin

Just that I wish I’d known atoms were so social back in school—it feels less intimidating thinking about them as, like, relationship charts instead!

Eric Marquette

Ha, that’s exactly the metaphor. And hey, for anyone listening who remembers us tackling molecular bonds back in episode 3, this time we’re really breaking down what those bond types mean for biology. Okay, should we dive into what these bonds actually do for living things?

Avery Lin

Let’s do it. So, water—this is where the polar covalent bond comes up, right? In water, oxygen’s that greedy atom, pulling electrons closer, so you get a partial negative end on the oxygen and partial positives on the hydrogens. That’s why water is polar. But can you walk me through how that makes water so... sticky?

Eric Marquette

Yeah, here's where hydrogen bonds kick in. That slightly negative oxygen on one water molecule gets drawn to the slightly positive hydrogen on another. So what happens? Water sticks to itself—cohesion—and to other things—adhesion. This is what lets water form droplets, makes bugs walk on puddles, and helps trees pull water from roots to leaves without having, like, a heart. It’s wild.

Avery Lin

Isn’t that called capillary action? The combo of adhesion and cohesion, right? Water clinging to itself and to the sides of a tree’s xylem, basically pulling itself upward. That’s why you get those long... what’d you call them, “strings” of water climbing trees?

Eric Marquette

Exactly! And not just trees—your blood vessels, too, rely on some of those same principles. This all comes from those polar covalent bonds and the weak (but many) hydrogen bonds between water molecules. And if you ever wondered why water’s such an amazing solvent—or why salt dissolves in it but oil doesn’t—it’s all down to those charges, and water’s polarity.

Avery Lin

So shifting to organic molecules... carbon is the headliner. It's got four valence electrons, so it bonds with up to four other atoms, and because it’s so small and electro-neutral—meaning it’s not, like, sticking to everything with a charge—you can build all sorts of shapes. Chains, branches, rings… like microscopic Lego. And that’s a wild mental image, but useful.

Eric Marquette

Yeah, and that flexibility is what lets you get everything from simple sugars to DNA and proteins, just by arranging carbons differently. And, here’s where functional groups show up—those little “add-ons” like OH (hydroxyl), carboxyl, phosphate—each one changes how the molecule behaves. Like, you stick a phosphate on something and suddenly, it’s attracted to water. Take it off, and now it wants to hide from water. These small tweaks completely change a molecule’s destiny.

Avery Lin

Right, so a fatty molecule? That’s just long chains of carbon and hydrogen—no charge, so it’s hydrophobic, not mixing with water. But tack on an OH or a phosphate and now it plays nice with water. And that’s why, like, membranes have both hydrophilic and hydrophobic parts. It's structure equals function.

Eric Marquette

That's the biggest idea. The way glucose bends into a ring, or the way a fatty acid can kink if a bond is unsaturated—it all controls what these molecules can do in our bodies. So when we’re talking about glucose or fats or proteins and scratching your head about why they’re shaped that way, it’s always about those carbon “arms” and the functional groups added on. Think of it almost as molecular origami, with serious consequences for living things.

Avery Lin

Alright, let’s get into the biological builders—the polymers! Ok, Eric, what makes a polymer, well, a polymer?

Eric Marquette

So, a polymer is just a whole bunch of repeating units—monomers—linked together. It’s like beads on a string, but each bead might be a sugar, an amino acid, or a nucleotide. Building these up usually happens through dehydration reactions—pulling out water to connect two monomers, like what happens when your muscles are growing and new proteins are assembled. Breaking them down? That’s hydrolysis—you add water to snap a polymer into its pieces, like digesting protein after a meal.

Avery Lin

That’s... weirdly poetic. And totally makes sense why staying hydrated matters for digestion! So, with carbs, the basic monomer is glucose, a monosaccharide. Two joined? That’s a disaccharide—think table sugar. Many joined, now you’re talking about polysaccharides like starch, glycogen, or cellulose. What’s the deal with how these are built?

Eric Marquette

It’s all about arrangement. Starch is mostly straight chains with just a little branching—found in potatoes, for instance. Glycogen, on the other hand, is the storage carb in animals and is super-branched, which means when you need energy fast, you can chop off glucose units from lots of ends at once. That's how your muscles can dump sugar into the bloodstream super quick during a run. Cellulose—in plant cell walls and what we call fiber—is lots of straight chains stacked and hydrogen-bonded together. We actually can’t break those bonds ourselves, so unless our gut microbes help, humans can’t digest cellulose, which is why fiber passes right through us.

Avery Lin

But cows and termites? Their microbes make special enzymes to bust up that cellulose for them. Also, shout-out to the gut microbiome—so cool to see a third of your calories can come from stuff your microbes process. And apparently, we can end up sharing our gut bugs with pets and roommates? Science is wild.

Eric Marquette

It really is. Now, lipids—those get lumped in as fats, but they don’t build up as true polymers. The classic one is the triglyceride: three fatty acid tails hooked to a glycerol head. Huge hydrocarbon chains, super hydrophobic—so, they don’t want to mix with water. And the structure again matters: saturated fats have no double bonds, so they pack together tight and stay solid at room temp. That’s like butter. Unsaturated fats have kinks from double bonds—can’t pack tight, so they’re liquid, like olive oil. And this isn’t just food science—the physical state impacts how fats move around your body, or stick inside your arteries.

Avery Lin

Okay, now, those phospholipids you mentioned set the whole bio world apart, right? Because they’ve got two tails and a phosphate head, so one part loves water, one part hates it. That’s how we get cell membranes—just throw a bunch of these molecules in water, and they arrange themselves into a double layer with hydrophobic tails inside and hydrophilic heads facing the water. Nature’s genius “no assembly required” packaging.

Eric Marquette

That’s honestly what blows my mind—the way simple chemistry roles like attraction and repulsion lead to something as complicated as a living cell. And while we didn’t get to proteins today—believe me, those are coming soon—understanding these carb and lipid basics sets you up for everything else we’ll hit in BIO 110. Avery, anything else you want to hit before we wrap up?

Avery Lin

Only that this stuff is weirdly empowering? Like, if you can picture these molecules doing a dance every time you eat toast or take a run, it feels less intimidating and more like, “Oh! Biology is just the story of molecules playing together.” Thanks for guiding us, Eric!

Eric Marquette

Anytime! And thanks for bringing all the questions—if you’re listening and have more, send them our way. Next episode, we’ll climb into proteins and amino acids, promise. Avery, always a pleasure!

Avery Lin

Right back at you, Eric. See you—and everyone listening—next time on BIO 110 Recap. Take care!