 Hi, today we're going to be talking about energy. All cells need energy to repair their membranes, to make new proteins, to reproduce. All of that requires energy. Now cells are kind of like little power plants. They're able to convert the energy from our food into something useful for the cell. In this particular case, the cells convert that energy into the form of ATP. But first let's talk about energy in general. So energy is defined as the capacity to cause change or the capacity to perform work. Now there's two kinds of energy, kinetic energy and potential energy. Kinetic energy is simply the energy of motion and potential energy is stored energy. So kinetic energy is where we have a moving object that can transfer its energy to another object performing some kind of work. So if you're playing baseball and you've got a moving bat, if you hit that baseball then you transfer that kinetic energy from the bat to the ball and then hopefully get a home run. Same kind of thing with moving water. Moving water coming down can spin a turbine, kind of like a pinwheel spinning. And that spinning motion of the turbine can then create electricity. So all of these things that are in motion can then transfer their energy to something else doing work. Now you might not think about it, but heat is also kinetic energy. Heat is where you have random movement of atoms or molecules. So if you have very little heat, these atoms and molecules are moving around very slowly. But if you have a lot of heat, these guys are moving around very quickly bumping into each other. So again, in that way as well, heat is also kinetic energy. So if you think about it, if you have a stove that you're warming up or heating up, that stove can transfer its thermal energy, the bumping of those molecules and atoms together to heat up our food or to cook our food. Now potential energy is different. Again, this is energy possessed as the result of a location or as the result of a structure. So you can think of potential energy taking the form of a battery. So your battery has a bunch of energy that's stored within it and then if you plug in your MP3 player or you plug it into your camera, then you can use that energy. Same kind of thing with water behind a dam. So water can build up and build up and build up behind a dam, but if that dam were to break or that wall to be removed, that water would flood out with a lot of energy causing a lot of devastation, knocking boy houses, trees and things like that. Or you can also think of potential energy as a person standing on the top of a diving board. So they have a lot of energy because of their height or their physical location above the ground. Now another type of potential energy occurs in the form of chemical energy. So we have a lot of energy that's stored in between the bonds of atoms. So you can see over here we've got a hydrogen bonded to a carbon. And so if you were to break that bond or karate chop between those two atoms, then you would be able to release energy. Same kind of thing here between the carbon and the hydroxyl group. If we were to karate chop that bond or break that bond apart, we'd release a lot of energy. So chemical molecules because of their structure also have potential energy. So let's talk about our two laws of thermodynamics. The first law is that energy cannot be created or destroyed. Now energy can't be created or destroyed, but it can be transferred or transformed into another form. So one way to think about this is dinosaurs used to be roaming the earth. They had a lot of energy in their muscles and their cells. And then when they passed on, they were able to transform that energy into oil. And then we can take that energy and we can convert that oil energy into electricity. We can take that electricity and transform it into energy to heat up our stove. And we can take the energy from that stove, that thermal energy, and use it to bake our food. So again, we aren't creating or destroying energy, but we're simply transforming it from one form to the next form to the next form. Now the second law of thermodynamics is that energy conversions increase the entropy in the universe. Now you guys might not be familiar with the term entropy, but entropy is simply a measure of disorder. So whenever you have random movement where atoms and molecules tend to spread out and spread out and spread out, you have more and more entropy. So it's kind of like if you have ten students and ten desks, the students usually will all sit at the desks. Now if you have ten students and a hundred desks, those students tend to spread out in the classroom in the exact same process with entropy. Molecules and atoms tend to spread out and have more disorder if they're allowed to. Now in most energy conversions, some energy is unusable. Some energy is lost in the form of heat. If you remember that heat is that thermal energy where you've got those atoms and molecules moving around. And when you heat something up, those molecules tend to bump into each other and get far apart. Bump into each other and get further apart so they spread out. So because most energy conversions generate heat, this also supports our law of thermodynamics that we're increasing the entropy in the universe overall. So here's two examples. One using a car and one using a cell. So when you're driving your car, you've got to have two things. You've got to have gasoline and you've got to have oxygen. So gasoline is an eight carbon molecule. You fuel up your car and then you turn on your engine. And what happens is your engine undergoes combustion and it creates carbon dioxide and water. Now carbon dioxide and water is not too useful for us, but in that process of combustion, we also create kinetic energy where we're able to move those wheels and move our car around. And then also, in addition to that, we create heat. And remember heat is increasing the entropy of the universe overall. So about 25% of our gasoline, all that energy from our gasoline, is used to move our wheels. So that means about 75% of the energy that was found in the gasoline is simply lost in the form of something unusable in the form of heat. And if you guys aren't familiar with this, if you've been driving your car around and then you accidentally stick your hand on the trunk of the car, that front part, you'll notice that it's really, really hot. And so that's, again, an example of this combustion producing heat. Same kind of thing happens in your cell. Except to fuel our cell, we often use glucose, which is a sugar, a six carbon sugar, and oxygen. Now that cell undergoes cellular respiration and produces the same two things, carbon dioxide and water. And then instead of moving the wheels of our car, because the cell, of course, doesn't have wheels, the cell is able to produce ATP. Now this ATP has potential energy. It's kind of like a rechargeable battery. And then we're also, again, creating heat. Now the neat thing about a cell is that a cell is much more efficient than a car. So whereas we're only using 25% of the energy of the car to do something usable, something useful, we're able to use about 33 to 37% of the energy found in glucose or our food in order to create that ATP for our cell. And then, of course, the rest of that energy is, again, lost in the form of heat. Now in winter time, some of that heat might be useful in keeping it warm. But in the summertime, that's, again, just a waste product for this cell. Chemical reactions. Now all chemical reactions either store or release energy. So we've got two types of chemical reactions, exergonic and endergonic. Exergonic reactions release energy or give up energy. So you start off with reactants. You create products. And then you also give off or create in a manner of speaking energy. Endergonic reactions are the opposite. This is where we store energy. So we start off with reactants. And we have to add in energy to the system in order to create our products. So if we don't add in the energy, we're never going to be able to get this chemical reaction. And so you can see that these two reactions, the exergonic and endergonic reactions are kind of opposites of each other. And so in our body, we often have these chemical reactions paired up or coupled with each other. So we've got one that will release energy and then one that will use up that energy. Now when you pair all of these reactions up and look at all the chemical reactions that occur in the cell, you end up with metabolism. So metabolism is simply all of an organism's chemical reactions that occur. And within a cell, you can have thousands of exergonic reactions, thousands of endergonic reactions in order to create all the materials that our cell needs to function. Now the way that this occurs is that our cell produces ATP. ATP stands for adenosine triphosphate. And so you can see that this molecule down here is ATP. So it's called triphosphate because it has one, two, three phosphate groups. And it has an adenosine part attached to it. Now ATP or adenosine triphosphate powers nearly all cellular work. And ATP kind of acts like a rechargeable battery. ATP is able to store energy that we get from our food. And then it's able to break this bond in between that second and third phosphate group. And when it breaks that bond or karate chops that bond, we're able to release the energy between those two molecules and use it for whatever our cell needs to do. So ATP, again, is where we have stored up energy. The cell is ready to do work. And then when we've used it up, we end up with ADP and a phosphate. So ADP stands for dye phosphate, where you only have two phosphate groups. And then we're able to regenerate more ATP when we eat food. And then we're able to use it to do cellular work and regenerate ADP. So it's a constant cyclical process where we're making and using up, making and using up that ATP. Now one way that we're able to use that ATP is to do phosphorylation. So this is where the ATP molecule is able to energize other molecules by transferring that third phosphate group over. Now this energy can again help the cells perform work. Mechanical work, transport work or chemical work. So for mechanical work, we can take that phosphate group from the ATP and transfer it to a protein. And when we transfer that phosphate group over to the protein, it causes the protein to change shape, change its three dimensional shape. And so for example, in our muscles, that can cause our muscle to contract. We can also transfer that phosphate group to a membrane bound protein, like a protein channel, again same kind of principle. When we transfer that phosphate group over to that membrane channel, it causes the protein to change its three dimensional shape. And now it might let ions through and put together membrane. And then third, we can use phosphorylation to do chemical work. So instead of transferring it to a protein, we can transfer that phosphate group to another molecule or another compound. And that's going to energize the reactants. It's going to provide enough energy to allow it to react with another molecule. And so then we can form a more complex molecule. So again, phosphorylation from ATP can allow us to do mechanical work, transport work and chemical work in the cell. Now cells continually make and use up the ATP. In a muscle cell that's actively working, it can make 10 million ATP molecules and also use up 10 million ATP molecules every single second, every second, every second, every second, 10 million ATP molecules. But in addition to ATP, in addition to this energy, our metabolic pathways also need biological helpers that are called enzymes. And we'll talk about that another time.