Video Transcript: Cellular Respiration and the Mighty Mitochondria

Cellular Respiration and the Mighty Mitochondria...

Are you a morning person? One of us is, and one of us is definitely not. Mainly because when I wake up in the morning, it takes a while for me to feel like I get my energy back; it takes a lot of time and coffee for that to happen for me.

Cells don't really have that luxury. They're busy performing cell processes all the time. And many of the processes that they do require energy, specifically ATP energy. ATP stands for adenosine triphosphate. It's a type of nucleic acid, actually. And it's action-packed with three phosphates. When the chemical bond that holds that third phosphate is broken, it releases a great amount of energy. It also is converted into ADP, adenosine diphosphate. And really, that's just a fancy way of saying that it has two phosphates after losing one.

So where am I going with this? Well, cells have to make ATP energy. It doesn't really matter what kind of cell you are. Prokaryotes or eukaryotes, you have to make ATP energy. The process for making that ATP energy can be different depending on the type of cell, but you have to make ATP energy.

One way that this can be done efficiently is called aerobic cellular respiration. We are going to focus on aerobic cellular respiration in eukaryotic cells. Remember that eukaryotes cells have many membrane-bound organelles, such as mitochondria, they're going to be kind of a big deal in this.

So, let's get started. Remember, we are trying to make ATP energy. Let's take a look at this formula. Remember that reactants, the inputs are on the left side of the arrow, and products, the outputs on the right side of the arrow. This formula, by the way, looks remarkably similar to photosynthesis. I mean, just look how the reactants and the products just seem to be on different sides. This isn't really a coincidence. See, in photosynthesis, organisms like plants and some types of protests, for example, they make glucose. Notice how glucose is a product. But in cellular respiration, we break the glucose. Notice how glucose is a reactant, in order to make ATP energy.

So photosynthesis makes glucose and cellular respiration, it breaks glucose, kind of cool. Now photosynthetic organisms, they have the best of both worlds, because really, they don't just get to do photosynthesis to make their glucose. They also get to do cellular respiration to break their glucose. I think it's pretty great because glucose is the starter molecule and cellular respiration. And it's needed in order to get all of this going. So if you aren't photosynthetic, like a human, or an amoeba, you have to find a food source to get your glucose.

Now cellular respiration involves three major steps, we are going to assume that we are starting with one glucose molecule so that you can see what is produced from this one glucose molecule. Now we're gonna start with the first thing: number one, glycolysis. This first step takes place in the cytoplasm. And this step does not require any oxygen. Glucose, which is the sugar from the formula, is converted into a more usable form called pyruvate. It's actually takes a little bit of ATP energy itself to get this process started. The net yield from the step is approximately two ATP molecules and two NADH molecules. What is NADH? Well, NADH is a coenzyme. And it has the ability to transfer electrons which will be very useful in making even more ATP later on, and we'll get to that in just a little bit.

Okay, number two is the Krebs cycle. This is also called the citric acid cycle. We are now involved in the mitochondria. And this step requires oxygen, the pyruvate that was made before it's now converted, and it will be oxidized carbon dioxide CO₂ is produced. And we produce two ATP, six NADH and two FADH. FADH is also a coenzyme, like the NADH and it will also assist in transferring electrons to make even more ATP. The third step is the electron transport chain. This is just a beautiful thing. We're still in the mitochondria and we do require oxygen for the step.

This is a very complicated process and we are greatly simplifying it and saying that electrons are transferred from the NADH and the FADH to several electron carriers, and they're used to create a proton gradient. The protons are used to power this amazing enzyme called ATP synthase. Really, if I could be any enzyme, I'd be ATP synthase. Because this enzyme takes phosphates and adds them to a DEP. And if you add one phosphate to ADP, you make ATP. So that's what ATP synthase does, it makes ATP. And it makes the ATP by adding those phosphates.

Now oxygen, it's the final acceptor of these electrons. And when you have an oxygen molecule combining with two protons, you get H₂O, which is water. So water is a product as well, the electron transport chain produces a lot of ATP compared to the other two steps. It's all because of that ATP synthase. There isn't an exact number on this, many textbooks will say that this step makes 34 ATP, meaning that the net amount of ATP when you add it, all three steps would be 38 ATP. But you need to understand that this is a perfect case scenario. And in general, you can't really expect that much ATP made each time.

Now if we look at our formula, again, we can see how the glucose and the oxygen on the reactant side were used to produce carbon dioxide, a waste product, water, which was a waste product, and ATP energy. ATP energy was our goal. Now this was just one way of creating ATP energy, a very efficient way of that. But like we said at the beginning, all cells have to make ATP energy. The way they do it, though, can differ if there is no oxygen available; some cells have the ability to perform a process known as fermentation. It's not nearly as efficient, but hey, it makes ATP when there's no oxygen.

Now, we really can't emphasize enough how important the process of making ATP energy is. If you don't help powerful does, consider cyanide. This toxin is found in some rat poisons. It is highly toxic, it works by blocking a step in the electron transport chain. And without being able to continue the electron transport chain cells can't produce their ATP. And this poison is deadly in a very short timeframe. There is also a demand for increased research on various mitochondrial disorders. Mitochondria are so essential for ATP production in humans that many mitochondrial disorders can be deadly. We are confident that the understanding of how to treat these disorders will continue to improve as more people like you ask questions. Well, that's it for the amoeba sisters and we remind you to stay curious