Hi everybody, this is the video for Chapter 23, the Metabolism Chapter. Now we don't have a set of outline notes for Chapter 23, instead I give you a homework assignment of the key concepts from Chapter 23. So you'll use that homework assignment, one, you'll get a grade for it, but two, that'll also be the portion of Chapter 23 that you'll study from. So you'll use that homework assignment once it's completed. You'll use that as if it were a set of notes. And that will be the concepts that I can test you on from Chapter 23 for Exam 3. So there are two concepts that I want to go over with you in this video.
One is just an overview of metabolism and what the two sort of components of metabolism are. And then finally, I want to talk to you about the absorptive versus. post-absorptive states of metabolism.
So let's start with just the general metabolism. So metabolism is an overall umbrella term that just refers to all of the chemical reactions that occur in your body. So there are two arms to metabolism, and they are anabolism and catabolism, or sometimes we call them anabolic reactions and catabolic reactions. So anabolic reactions are reactions that build larger molecules.
So we call these building reactions. In chemistry, instead of calling them building reactions, sometimes they're referred to as synthesis reactions. So in these reactions, you are taking many small molecules and linking them together to build one large molecule. An example of this would be taking many glucose molecules. Remember, glucose is a monosaccharide.
It's very small. Taking many glucose molecules and building the larger storage molecule called the glucose molecule. glycogen. That's an anabolic reaction.
Because this is a building reaction, it consumes energy, it uses energy. So we also call this an endergonic reaction. Endergonic. Okay. So again, an anabolic reactions or anabolism are building reactions or synthesis reactions.
They take smaller molecules and link them together to build a larger molecule. An example would be many glucose forming the large storage molecule called glycogen. And anabolic reactions tend to be endergonic. That means they consume or use energy. So now that you know what anabolic reactions do, you should be able to tell me the opposite.
for catabolic reactions or catabolism. So if anabolic reactions are building reactions, then catabolic reactions have to be breaking down, right? The opposite of building would be breaking down. We call these reactions decomposition reactions.
I'm running out of room. Decomposition reactions. So a good example would be the opposite of what I just gave you.
That would be taking a storage molecule called glycogen. We store glycogen. It's an energy reserve molecule. We store it in our liver and our skeletal muscles.
We take glycogen. And when we need extra fuel, we need extra energy. We break down that glycogen into smaller glucose molecules.
That's taking a large molecule, glycogen. breaking it apart into smaller molecules called glucose. That is a catabolic reaction.
All of the reactions we talked about in digestion, taking a large molecule and breaking it into a smaller components, they are catabolic reactions. Because we're breaking bonds, we are releasing energy. So in catabolic reactions, these are predominantly exergonic reactions. That means they release energy.
So again, metabolism is your overall umbrella term for the reactions that occur in the body. They are broken down into anabolic reactions and catabolic reactions. Anabolic, building or synthesis.
Catabolic, breaking down or decomposition. Anabolic are endergonic. That means they consume or use energy. Catabolic are exergonic, meaning they release energy. Good.
Now, the last... concept I want to talk about on this video is the absorptive state versus the post-absorptive state. And we see this when we're talking about athletes who are in endurance sports.
So if we're talking about like a marathon runner, someone who needs to store extra energy to be able to tap into those energy stores during their endurance event. You know, a marathon is 26.2 miles. You're not going to stop in the middle of a marathon and eat, you know, pasta dinner. You don't have time for that. And you certainly will cramp up doing that.
So endurance athletes, marathon runners being an example, have to make sure that they're fueling properly, right, they're eating properly, prior to a race or prior to their event, so that they have enough nutrients available to them for their duration of their events. A marathon can be, you know, three hours, four hours, five hours of running without stopping. So you need that energy.
So there's something called in endurance events, carb loading, you may have heard of it before. So It's usually like two days before the event, the athlete will ingest a large portion of carbohydrates. Now we know that when we ingest carbohydrates, we break down the carbohydrates all the way down to monosaccharides. And then the cells will use the monosaccharides, predominantly it's glucose, and they'll use as much as they need. But if you're carb loading, that means you're taking in more carbohydrates than your cells need.
So what your body does is the ones, the carbs that you don't need at the very moment that you're consuming the carbohydrates, your body will put the extra carbs into storage. And this is what happens during the absorptive state of metabolism. So during the absorptive state, you're consuming carbohydrates.
You have an excess amount of carbs. So the cells have used the glucose that they need to use and you just have an extra. So what do you do?
You don't want to leave all that glucose in your blood. That's not good. So we have to put the many glucose that you have in your blood.
We need to put them into storage. And the storage molecule is glycogen. Glycogen is a large molecule that stores carbohydrates, stores this energy.
We store it in our liver and our skeletal muscles until we need it. Right. So this is the essence of carb loading.
This is what's happening during the absorptive state. The hormone that drives this is insulin. Insulin is the hormone that drives this. So we again, we ingest. a lot of carbohydrates.
We break them down into many glucose. We absorb all that glucose. We don't need all that glucose. So instead of just getting rid of it, we put it into storage for later use.
That storage molecule is called glycogen. We store glycogen in our liver and our skeletal muscles. The name of this process, right? It's the absorptive state of metabolism, but the name of this reaction, taking many glucose and And converting it into glycogen is called glycogenesis.
Glycogenesis. Glycogenesis. Genesis means to create. We're creating glycogen.
Okay. Now let's talk about race day. So during race day, right, this is this is happening maybe two days prior, you're two days out, you're going to carb load.
On race day, you're on the post-absorptive state. So race day, you wake up, you're not going to eat a large meal. You eat whatever you've been eating on your training runs and you're ready to go. You're ready to go. You have fuel stored.
The storage is the glycogen. Okay. So you start running, the athlete starts performing whatever endurance event they're going to do. And this is the post-absorptive state. This is when you haven't eaten for a while.
You don't have glucose coursing through your blood. You have to tap into your stores. So you're going to turn to your glycogen stores and you're going to break down that glycogen and release the glucose into your blood. The cells then can use the glucose to continue to make energy, to continue to perform. So our muscle cells, right, if you're running a race, you need your muscle cells to have that constant.
glucose supply to continue to, you know, help with contraction. So this is the reverse of the, the first equation that we went, we went many glucose to glycogen. Now we're going glycogen to many glucose.
The hormone that drives this is called glucagon, right? This is the hormone glucagon. Um, I always joke with my students in biology 109. You can remember that it's glucagon because this hormone is released when all of your glucose is gone. Glucagon. So whenever you need to have more glucose in your blood, glucagon is released to break down glycogen into many glucose.
This reaction is called glycogen. Glycogen. O lysis lysis means to break apart.
What are you breaking apart? You're breaking apart glycogen glycogenolysis. So hopefully that clears up the absorptive, right?
Preparing for your race, insulin driven, making glycogen versus the post absorptive race day, tapping into your glycogen stores. releasing the glucose for instant use, um, states of metabolism. Thanks everybody. Good luck with the chapter 22, um, homework assignment.
Email me if you have any questions.