Hello chemists Michele Glass here and thank you for joining me for another one of our chapter two lecture videos. The topic here is metabolism which is something you've probably thought of before, right? You think about like how much food you eat and then maybe how many calories you burn and kind of in the context of like gaining weight or losing weight, right? And that's true. That's definitely part of it. But this is more of a broad idea than just this idea of the calories you eat and the calories that you burn. Metabolism here is talking about all of the chemical reactions that take place in the body. And notice I'm using an abbreviation rxn as a shorthand for reaction. So you'll see me use that throughout. When we talk about all of the chemical reactions in the body as metabolism we can then narrow it down into categories. So we have anabolism which is synthesis or making reactions. And then we have catabolism which is the breaking down or decomposition reactions. Now these go hand-in-hand. Obviously so you eat food and all of the processes starting in the mouth, continuing in the stomach, and small intestine is to break down or catabolize that food into nutrients that your cells can use. And those ingredients, those nutrients are put into the bloodstream and then taken around your body to your tissues. And then your tissues use those components, use those nutrients, in order to build new molecules whatever molecules your cell needs, right? So that's what we're talking about here. We also need to talk a little bit about energy. Energy is defined as the ability to perform work. And you've studied this before probably in middle school and high school. We have what we call kinetic energy which is the energy of motion and then we have what's called potential energy which is stored energy. Now for us and our bodies that potential energy is stored often in chemical bonds. So very often we have chemical reactions that break chemical bonds releasing that kinetic energy to do work in the body. We can also talk about reactions in terms of their energy need. So we have reactions that can be classified as either endergonic - endergonic reactions are going to absorb or use energy or we have exergonic reactions and these are going to be reactions that actually release energy. Now if you were to feel these an endergonic reaction would feel cold and an exergonic reaction would feel hot with that release. So exergonic reactions we feel this and see this very easily. When you move your body and you're increasing your skeletal muscle movement you're also conducting exergonic reactions in order to release energy and so you're generating heat, right? When you burn wood you're breaking down and releasing the stored energy in that wood and so you're releasing energy. That's exergonic. You see that energy in the form of light and you feel it in the form of heat. Hot hands are a product that's using an exergonic reaction to generate heat. So you can be camping in the woods and keeping your hands warm. Endergonic reactions would feel cold. We don't maybe have as many great examples to give right here things from everyday life but if you've ever used like a an automatic cold compress where you have a chemical reaction that's generating cold just kind of like the opposite of a hot hand that would be an example of an endergonic reaction. Let's talk also here about what's called activation energy. Oh y'all I had a mad sneeze come on there and I hope I paused everything in time! So if you saw me act crazy that's what was going on. We were talking right there as the sneeze was hitting me we were talking about activation energy. And here we can talk about this as the energy required for a reaction to occur. And we're going to talk more about this in just a few minutes when we look at enzymes. Before we do that, let's look at how we write and talk about reactions. So we use this sort of equation format. And we also, always on the left hand side, write our reactants left hand of the arrow. And then we always put our product on the right hand side. Now here because we are bringing A and B together in order to make AB this would be an example of an anabolic reaction. If I added energy here on this side as part of a product so if in this reaction we also release energy then that would make it exergonic. Okay I can just do a little modifying here I can make this - put the energy as a reactant - and now I have an endergonic reaction. And then I can change the direction of my arrow. So if I draw my arrow the other way. Now I see that I have the - that would change all of this, right? So let me do that too because I've moved my arrow. Let me just... Let me keep this here. Let me actually just rewrite the equation so now let's go AB into its components A plus B. So when I've written the reaction like this, this would look like a catabolic reaction. We could do those same things playing around with writing energy as either a reactant or a product and that would help us to see whether it was endergonic or exergonic. Next we're going to look at that enzyme and its significance in what we call energy of activation. And we're going to do that on this kind of graphical representation. So take a minute for yourself on the left hand side you are writing "energy" which is going up and then on the other side it's the progress of the reaction. So kind of looking at like time in a way there. And give yourself kind of like this dotted line for reference sort of in the middle. So pause if you need to. Okay so what we're going to do with this is look at what happens with this reaction. So we have A plus B kind of going along and then in order for the reaction to occur...it's not a great drawing... Right what we're showing here what we're trying to represent is that energy of activation. So very often chemical reactions require temperature as a factor that influences reaction rate. So very often increasing the temperature increases the rate of reaction. What this would say is you know chemical reactions are typically getting A and B in close proximity to each other so that product AB forms, right? If you increase the temperature you're moving those molecules around faster they're more likely in contact with each other the reaction happens faster. This is so great in the laboratory. This is so great in the kitchen. It's so not great in your cells. You can't heat up your cells in order for your reactions to occur in a timely fashion. Everything's gonna be damaged in that case, right? So temperature is a factor that influences reaction rate but it's not a factor that fluctuates in the body very much. We also see another factor that influences, so I'm talking about concentration. So how much of those reactions... those reactants do you have? It makes sense the more reactants the more product so if you increase your concentration you typically increase your rate. Another factor that matters is the surface area of the molecule. Surface area is talking about how big that molecule is. If you have a really big molecule and you're trying to break it down into its little components it's going to take longer than if you have a smaller object. So part of what we're doing like in our digestion it starts in our mouth and part of this mechanical just like chopping up the food that we eat trying to make the food material smaller and then those molecules are actually getting ripped and torn as well. So making those smaller. And then the fourth factor that's involved here are enzymes. Enzymes we've mentioned I think real briefly before. And we're going to talk about them more in a later video. Enzymes can be described as catalysts. And what they actually do is they reduce the energy of activation. So in the graph, going back to the graph we drew, like it takes this much energy in order for A plus B to actually form into AB a stable product. And in the lab, in the kitchen, you can speed that up with temperature. Maybe this reaction spontaneously occurs in the cell but maybe it takes like 10 years. We can't wait 10 years for our reactions to occur, right? We need them to occur in a timely fashion. And this is where your enzymes come into play. So what your enzymes do is they bring A plus B closer to each other such that less energy is required to get you to the AB. So if we're doing A plus B they fit in together in this enzyme in such a way that they can form this new bond more easily. If we're talking about a catabolic reaction then maybe they fit in in such a way that it sort of like stresses out the bond making it easier to break. In some way the enzyme is involved in making this reaction occur faster. The enzyme is not changed or used by being part of this reaction. So we'll typically write it over top of the arrow. So you might put your enzyme here. The thing that's super significant about these enzymes is that you know basically you should consider in your body and your cells no reaction is taking place without an enzyme. And every reaction has its very own enzyme that catalyzes that reaction. Okay so stay tuned to hear more and in the meantime take care of yourself and each other