 Hello. Let's learn a little bit more about cellular respiration. Glucose is a monomer. It's a monoseccharide that is extremely important for our functioning, not just for our functioning as human beings, but for a variety of organisms. This is the shape how glucose looks like. It's a hexose and a formula of it. Now, there are different things here. If you think about fibers, there's plenty of fibers in the spring onion, and those fibers are in the form of the cellulose, which is in the cell wall of the plants. Can we digest it? We cannot digest it. But that spring onion can be sometimes sweet, which comes from the sugar. And guess what? Glucose is part of it. Bread that we eat. Bread, the base for the bread is flour, which is, in most of the cases, starch sometimes with additional parts, sometimes just plain starch like in white bread. And that is also polymer of the glucose, but that is polymer that we are able to digest. Some of the glucose here in the fiber is in this piece of wood in the board. Can we digest it? Now we can't. When you have fireplace and you start the fire, that energy that is released, that is warming you, is actually, think about it, that's your own sunshine, that's your own sun, that has been transformed into chemical energy through the process of photosynthesis and building all the plants, in this case trees, tree branches, and now is with the help of the oxygen released, and we are utilizing that energy in the form of heat. So, photons are the ones that are carrying the energy. Who is doing the conversion of the energy on planet Earth? Green plants have in their cells organelles that are called chloroplasts. Chloroplasts have structures, their inner membrane is in the form of telequades, and that is where the pigments who are capturing the energy of the photons are converting that energy into chemical energy. They are utilizing carbon dioxide from the air, and the plants are taking water from the ground, and from these two molecules together with photons in the process that is called photosynthesis, glucose is formed. Further, glucose is either captured in the form of starch or built in the form of cellulose and transferred into other molecules. I need to emphasize here that during the process of photosynthesis, this is what is happening in the plants, but we often forget that plants are also organisms that need energy. So, part of that glucose that is built in the plants is utilized by the same cells, by the same energy, to build the energy that is needed for all the living processes that are happening, for growth, for building materials and so forth, and that energy is utilized from mitochondria. Mitochondria are organelles that we can think about that there are power plants. Now, photosynthesis and cellular respiration are processes that are opposite to each other. So, during the photosynthesis, plants are utilizing carbon dioxide and water in order to form glucose, and as the byproduct, oxygen is released. In the cellular respiration, we need glucose as the source of energy, that energy that is captured as a chemical energy, and with the help of the oxygen, we are retrieving the energy, utilizing that energy in a released water and carbon dioxide as a byproduct. So, energy is the key, right? Now, I need to say something here. What are similarities between chloroplasts and mitochondria? You have learned about the organelles, but I'm not sure how much you really know about who proposed the endosymbiotic theory. You've heard about Carl Sagan. His wife, Lynn Margulis, was the one who proposed that there is some extracellular DNA in the eukaryotic cells, which was blasphemy at the moment when she did it. However, it was proven that that extracellular DNA, the extra nuclear DNA that is within the cytoplasm, but outside of the nucleus, is actually coming from mitochondria, okay? Further analysis proved the DNA that is in mitochondria is not the same as the DNA that is in our nucleus. Mitochondria can divide by themselves in the same cell. You know, when you're building your muscles and then your muscles are growing, that is actually multiplying mitochondria that is happening inside. If we are becoming couch potato, then, hey, no need to maintain those power centrals. So the number of mitochondria is going down and our bulkiness of the muscles is going down, too. So, similar situation is with the chloroplasts. So both chloroplasts and mitochondria have the outside membrane, very important to remember and have inner membrane, which Lynn concluded that what happened is that long time ago when the life began, small prokaryote organisms made a symbiotic relationship with some of the eukaryotes and it turns out to be really good and productive combination. So, let's see what is happening during the process of the cellular respiration. Remember ATP, the nucleotide, AMP, ADP, ATP, these are the keys that you really need to have in mind. Let's say that this chemical energy that is captured by the plants and that we are intaking through our food, in order to be utilized, if we were to release all that energy that is packed in one molecule of glucose, it would probably burn, it would be too much. And it would be too much waste that we wouldn't be able to capture and utilize it for our own needs. So, who is that magic molecule that is capturing that energy and is helping us to utilize it? That is adenosine triphosphate, ATP. Please have this in mind. The one that has only two phosphate groups is ADP, so they're interchanging with the help of the enzymes. Now, how come that these are the ones that are capturing the energy? What it has to do? What is with AMP, ADP and ATP? Phosphate groups have the same negative charge. What happens when you try to put two of the magnets that have the same polarity if you try to put them together? It never happens that they can be next to each other successfully. I don't know how about you, but it never happened to me. So that means there was a tremendous amount of energy that was needed to put those together. There is an enzyme that is doing that job that has capacity to link them to make the bond. But that bond is really strong and they're just bursting with energy. So, obviously, there is more energy that is captured in the ATP molecule that has three phosphate groups next to each other than ADP that has two phosphate groups next to each other. And that is, again, more energy than compared to AMP. So, that is the process of... Kynase is the enzyme that is bringing the phosphate group to the molecule. What is happening and where? The process of cellular respiration, the first part of the process of cellular respiration is called glycolysis. And to make it a little bit easier, I have here illustration only of the mitochondria, even though other organelles and everything else is within the cell. But let's focus on mitochondria. Glycolysis is the first part of breaking down glucose. Glucose is broken first to pyruvate, which you will see soon, with use of the ATP molecules, which are bringing the phosphate group to the glucose, energizing it in order to proceed with breaking down glucose. Now, after that, the next step is Krebs cycle or citric acid cycle that is happening in mitochondrial matrix. So, this is the outside portion, outside membrane of the mitochondria. This is the inner membrane of the mitochondria, very important to remember. Inside of the inner membrane of the mitochondria, that part of the organelle is called matrix. And that is where Krebs cycle or tri acid cycle is happening. After that, the final portion of the cell respiration is electron transport chain or oxidative phosphorylation, which is happening embedded in the inner membrane of the mitochondria. That is also one of the leads for that endosymbiotic theory, because if you just imagine that this used to be a prokaryote that was on its own, today our prokaryotes that we know, like Escherichia coli or E. coli, have the proteins that are needed, enzymes that are needed for breaking down glucose that are embedded in their membrane. So, let's see, here are the parts. So, glycolysis is the first portion of breaking down the glucose Krebs cycle or citric acid cycle and electron transport chain or oxidative phosphorylation. That would be general about cell respiration.