Biochemistry of Carbohydrates

Hello, everyone. And welcome to the RDA exam ready podcast. I'm your host Zach Kspurk, here to be your tutor, coach, educator, on your path towards passing the RDA exam. As you walk this path, you're going to need to have some honest conversations with yourself and that honesty might reveal that there's topics you're just not strong in, at least not yet. We all have our stick points and the one that I consistently see people tripping up on is biochemistry. This is often one of those subjects people avoid. Maybe it was a class you had to retake, like in my case, or the one where you didn't score well. Or maybe it's the one you just hope doesn't show up much on the exam. Remember as your coach, it's my job to encourage you to believe that you can get better at anything, any of these topics or subjects. If you adopt a mindset that just says, "I'm just not good at this," well, then you're probably not going to be very good at it, are you? But if you challenge that belief, if you explore different ways of learning and keep trying new methods, you absolutely can overcome this thing. So I encourage you to try all kinds of approaches, even the unconventional ones. Let's talk biochemistry today. On the CDR exam, biochemistry is actually focused on a lot of the basics. And while it may not feel basic while you're studying it, trust me, the exam does not dive in deep end of the biochem. There's much more that could be brought up, but it's not needed for the CDR exam. That's good news. What's most important for the exam is understanding the inputs and the outputs of these key processes of biochemistry, where they happen in the body, and what conditions trigger different energy systems. Study tips for biochem include things like drawing stuff out, using note cards and showing them in a series, creating visual flow charts or animations in all kinds of PowerPoint tools or whatever you can use online to show things and how they move through biochemistry. You might even try telling it like a story. For example, imagine you're explaining how a patient is trying to lose weight and talks about those energy systems. Turn that science into a journey or a story. What we'll start with today is going to be glycolysis. Let's begin with glycolysis. It's the natural place to start. As a reminder, we're only going to need to know the major inputs and outputs of glycolysis in this process. Glycolysis is the process where glucose is broken down into two three carbon units. Those units are called pyruvate. Their input to this process is one glucose molecule. Where it happens is in the cytoplasm of the cell, and the conditions in which it's going to occur could depend. There's times where we can have aerobic conditions, and if you know aerobic, then you know it means with oxygen, or it could be anaerobic, which you should know means without oxygen. Colossus can happen in either of these circumstances when we have plenty of oxygen or plenty of breath, and when we are out of oxygen. When you're going for a walk, you could think of this as aerobic versus sprinting down the street that's anaerobic. Glycolysis can still happen in both these cases. Now glucose is going to be phosphorylated to become glucose 6 phosphate, and this is a form that you're going to see pretty often. It's an intermediary form of glucose that a lot of things end up as. Just keep that in mind. It's just glucose. As glucose moves through glycolysis, what is occurring is you're actually having to spend a little bit of ATP off the get go. You're spending a little bit of cash to get glycolysis running, cash or ATP. You spend two ATP right up front to get this process initiated. Here's the good news. You're going to make four ATP at the end of glycolysis. Two spent in the beginning, four produced at the end, for a net gain of two ATP. Make note because this is going to pop up later. Your key outputs as we go through glycolysis when we move the glucose to glucose 6 phosphate, and go through all of glycolysis to make pyruvate. At the end, you end up with two pyruvate molecules, two net ATP and two NADH. We're going to come back to NADH soon. What happens with pyruvate? Well, that depends on a couple of things. It depends really on if you're aerobic or anaerobic right now. After anaerobic conditions, the pyruvate does not go into its next step of entering the mitochondria. Instead, it stays in the cytoplasm and it ends up going through something called the quarry cycle. The quarry cycle is where pyruvate is being converted to a molecule called lactate or lactogacid. That lactate can be then used later in things like gluconeogenesis, which creates new glucose. But here's the catch. This quarry cycle, this gluconeogenesis, it doesn't produce a lot of ATP. It's inefficient, it's slow, we're mostly recycling glucose to make new glucose. Consider to how sprinters, lifters, they end up building a good deal of this lactic acid in their muscles. And that's when they're exhausted. So we know that this cycle probably isn't the best outcome for pyruvate. But we can talk about what is the best outcome for pyruvate? That would be the TCA cycle, the citric acid cycle, the creb cycle, as it's also known. You can use all of those, but I'm just going to call it the TCA cycle. Your energy from pyruvate is going to be much better used in the TCA cycle. And this is where we start really going through the process here. Now TCA cycle or the creb cycle can only be done in aerobic conditions. It's like a central to all of our macronutrients because many of the byproducts of biochem end up being used in the TCA cycle. So it's kind of a crossroads for your carbs, fats, and proteins. Today we're just focused on carbs. So first, pyruvate is going to be converted to a Cedal CoA inside the mitochondrial matrix or inside the mitochondria. The TCA is going to require magnesium, thiamine, riboflavin, and niacin. So keep in mind, these are going to be some important nutrients. Once a Cedal CoA is formed from pyruvate, acetyl CoA is then going to combine with a molecule called oxaloacetate. And this is the step one of the cycle here is when the acetyl CoA combines with oxaloacetate to get the TCA cycle running. Now while this TCA cycle is so essential, one note is is actually does not produce much ATP itself. That's the catch. The TCA cycle does not produce a lot of the ATP. It really is going to, we're going to produce the ATP later on in these stages. But from the TCA, you can picture what it looks like. It's a large circular cycle. It starts with that acetyl CoA. And the acetyl CoA is broken down into many, many intermediate, intermediate throughout that process. And as we're going through each of these intermediate, we're kicking off some outputs. Here's the important outputs you need to know from that. We get water from the TCA cycle, carbon dioxide, GTP, which is similar to ATP. And we also get three NADH and one FADH2. A few of these outputs need to have some context for you. NADH and FADH are two different co-enzymes that are produced here. NADH actually contains niacin. And FADH2 contains riboflavin. So that's so cool how you can see how those B vitamins really assist with energy and metabolism. They have a value. These NADH and FADH2s are actually more like checks that someone gave you. They're not cash yet. They do have a value, but you need to take them to the bank to cash them out. We're going to take them to the bank later and the bank is going to be called the electron transport chain. I also mentioned another output here, GTP, which is very similar to that of ATP. This came out of the TCA cycle. My analogy is that GTP is like a foreign currency. It's not a US dollar. It's pesos, it's yen, it's a British pound, and you need to convert it over it to make it ATP or cash. So GTP, it is energy ready to use. You just need to convert it before you go. or you can spend it. Now let's talk about the bank. The electron transport chain bank, this is where the real ATP production is happening folks. Remember how glycolysis and the TCA cycle produce that NEDH and FADH2? Remember the analogy, they're not cash yet, but they're checks that I need to take to the bank here. NEDH2 and FADH2, they're gonna enter the electron transport chain. And they enter on side A. On side A, they end up donating these hydrogen ions, those H's that they have, and they drop them off in those hydrogens, move over to side B. Okay, so NEDH and FADH2 stop by, they drop their hydrogens off, and the hydrogens go over from side A to side B down on the bottom. Now what happens is you have this large gradient that occurs. A gradient is when you have a lot of one thing on one side and not a lot on the other side. As a result of that NEDH and that FADH2, dropping all those hydrogens off, we now on side B have a ton of hydrogens, like a ton. So what our body likes to do is reach an equilibrium. It says, hey, let's shift these hydrogens over to side A. Each time that our body decides to take that hydrogen ion and take it back over to side A, it runs it through a special channel. That special channel is known as ATP synthase. So think about that. Every time an eye, a hydrogen ion is passing through ATP synthase, it creates an ATP. So as the hydrogen flows, the ATP is created, and so on, and so on. Final tally at the end of this, from one glucose molecule going all the way through TCA, then through the electron transport chain, you produced in theory about 38 ATP, which is a lot. In reality, you probably net about 36 ATP because you did end up spending ATP in the beginning to get this process running. Hopefully you enjoyed that to kind of know about glycolysis and how we're going to use that energy. We've talked about how we can now use the glucose to make energy, but what if we want to do something else with it, folks? Let's start with a few key hormones to make sure you know here. We have insulin in glucose gone. Insulin is what's known as your fed hormone. It's very active after periods in which you've eaten and you have plenty of nutrients available. Insulin job is to help open up those cells so that the glucose can then enter the cells, and it can usually be stored, but it also can be used for energy. So insulin is the fed one that says, "Hey, let's pack on more glycogen. "Let's pack on more fat." It's also a little bit active during glycolysis too, because it's trying to open up your cells to let the glucose in. Insulin then kind of encourages the cell to start glucose if it needs ATP, because it allowed the glucose to then enter the cell. Do you see? Glucogone is the opposite. It's the fasted hormone. It gets activated in periods of a low-food intake, installation. Its job is to help your body take stored energy and convert it to usable fuel when you haven't eaten for a while. So what happens with glucose would you don't need it right away? Let's imagine a situation like post Thanksgiving dinner, you be in multiple servings and your body is full of glucose. What happens to that excess glucose? One spot it could be directed is to glyco genesis. Break down that word with me, glyco, glycogen, genesis creation. So glycogenesis is the creation of glycogen. Glycogen is this branch storage form of glucose and it's found throughout your body. The majority of it is gonna be stored in your liver in your muscle tissue. Smaller amounts can be stored in your kidneys, your heart, and other tissues too. The liver can store about 100 grams of glycogen and the muscle is because there's a lot more muscle in the body usually can store up to 500 grams, 'cause there's a lot more muscle in your body than there is a liver, for instance. So this process of forming glycogen from glucose is driven by insulin, your fed state hormone, which is typically released when there's plenty of nutrients and food. The glucose molecules are going to go into the liver, go into the muscle, and they're gonna be formed into branched molecules called glycogen. Again, then it's just gonna be held for storage in the liver and the muscle for when we need it. It's just stored glucose, so what are we gonna do? At some point, we're gonna break it down when we need it. That's why we have it. That breakdown process of accessing that store glycogen is known as glyco-geno-licis. Break it down with me. Glycogen, the molecule, lysis, breakdown of. This is when we're breaking it down to access that stored glucose. This process is primarily activated by glycogen, your fasting hormone. When glycogen is released, it's signaling the body to break down glycogen so we can use that glucose. Glyco-geno-licis occurs in both the liver and the muscle, but there is an important difference between the two. Liver glycogen is broken into glucose that can be used all throughout the bloodstream and even the brain. Muscle glycogen, however, is different. Muscle cells lack the enzyme needed to convert glycogen into this free glucose. This means that the glycogen that is broken down in the muscle can only be used within the muscle itself. It's not gonna be able to be sent to other areas of the body. Another area in which we can use glucose or create glucose is in glucose, neo-genesis, the process of making glucose from non-carbohydrate sources. Let's break it down. Glucose, glucose, neo-new, genesis, creation. Gluconeo-genesis. This process occurs only during periods of low carbohydrate intake when your blood glucose levels are low. When this happens, glucagon in other hormones, such as norepinephrine, napinephrine, start to create glucose from non-carbohydrate sources. And these non-carbohydrate sources or inputs are gonna include these things. Lactate, glycerol, in certain amino acids. These are gonna be the three major inputs towards making new glucose. The liver is the primary site of gluconeogenesis, which makes sense. The liver glucose that is created can then be used all throughout the body, the brain. We wouldn't wanna do this in the muscle, for instance, because then you're just using glucose in the muscle and that's no good. Interestingly, many of the steps of gluconeogenesis are actually just the reversal of glycolysis. Instead of breaking down glucose into pyruvate, the body uses ATP and donated hydrogen ions to make a pyruvate into a glyco- excuse me, a pyruvate into a glucose here. More on the inputs of gluconeogenesis, let's look at these inputs to make sure there's no confusion. Amino acids were one of those inputs that could be used after your proteins are broken down. You have these leftover amino acids, and specifically there's glucogenic amino acids that can make glucose. And those actually end up being converted into pyruvate, oxaloacetate, or other intermediates that feed into gluconeogenesis or the TCA cycle. So the way you can think of this is the amino acids are just being created into pyruvate, the pyruvate being made into new glucose. Lactate, remember that Cory cycle from earlier? Under anaerobic conditions, like intense exercise, pyruvate is converted into lactate, which travels to the liver. In that liver, the lactate is gonna be converted back into glucose through gluconeogenesis, and that glucose can be sent anywhere throughout the body, remember. The third one was glycerol. Think of your triglycerides, which is that stored form of fat. That triglycerides have one glycerol head in three fatty acid tails. When fat is broken down, that glycerol head is released, and that glycerol head is able to travel to the liver where it's then converted into glucose via gluconeogenesis. Now, you know all the major pathways your body uses to manage carbohydrates, whether it's using glucose for immediate energy, story for later, or making new glucose from other sources. These are going to be the key biochemical concepts for carbohydrate metabolism and what you need to know for your exam day. But don't stop there. Take what you've learned from this podcast and build on it. Use your textbooks, create diagrams, draw arrows, showing glucose, becoming pyruvate, moving through the TCA cycle, and so on. Keep the repetition up and use all different learning styles, visual, auditory, kinesthetic to try to go about learning this biochem. Stay tuned because in the future and other episodes we'll end up diving into other areas of metabolism and other macronutrients. But that wraps up today's lesson. Don't forget to like, subscribe and share the podcast if you're enjoying the RD exam ready podcast. I'm your host Zach Kaseberg and happy sending to you RD2B.