 Now, we have these funky players that we haven't really been introduced to yet, and they are electron carriers. And electron carriers are really, really important. Now, you can think of an electron carrier as a car. And this car has a name. It's NAD. And right now, NAD is not carrying any electrons. But if we add two electrons into this mix, NAD becomes NADH, and I don't know, maybe I should try to give it a slightly different color to show that now it is a high-energy electron carrier, NADH. And these electrons are literally attached to it now. How cool is that? Okay, who cares? Except those high-energy electrons. Let's make a note of that. These guys, they're not normal electrons. They're like superpower electrons. They're high-energy electrons. And I'm happy to talk to you about why they're high-energy. Like, it really is a real thing. I think about them as just being like these little rock stars that bounce around really high. And they have a lot of kinetic energy, kind of like sort of the way that I think about it. But I can explain to you how it really is if you really want to know. But I'm cool with you just accepting that they're high-energy. And NAD, it's actually, NAD plus is empty. It's not carrying any high-energy electrons. If we add some high-energy electrons to it, now it's NADH and it can take those high-energy electrons and basically cash them in for ATP. Which, think about that for a second. We know ATP is an important molecule for living systems. We know it's basically the energy currency for our whole existence. And if the NADH, the high-energy electron carriers, can cash in those electrons for ATP, dude, that's magic. There are multiple high-energy electron carriers. There's another one called FAD. And FAD turns in, if it's carrying two high-energy electrons, it becomes FADH2. And again, we can totally, in fact, the actual breakdown of the molecule itself is not as important to me as you knowing that this molecule, two high-energy electrons can be carried by this molecule. And those will come in handy in our whole process. I think it's worth taking some time to talk about the fact, like to talk about ATP a little bit. ATP is an adenosine, adenosine, that's the A, triphosphate. And there's three phosphate molecules attached to the adenosine. And it doesn't take a whole lot of energy to break off that phosphate, the terminal end phosphate, and get a P plus ADP. Look at what I'm doing here. I'm just drawing it backwards, adenosine, and that's adenosine, diphosphate. Let's write that down, ADP, ATP. And I just drew it out for you so that you could see the chemical bonds that are important in this process. If you break the chemical bond between the third phosphate and the second phosphate, this little lonely phosphate now, the guy right here, is going to form a powerful, crazy powerful bond with water and release a doodoo load of energy. And that energy can be used to do work. That's actually the phosphate, the single phosphate forming a bond with water is actually where all the energy in ATP comes from. And then ATP breaks off that terminal phosphate and becomes ADP. This is important. We want to build ATP. In order to do that, we have to have ADP and P. And we have to, like, rip the phosphate off of the water molecule, you basically are water, and combine it with ADP. And this process, like, where are we going to get the energy to make this happen? How are we going to do this because it's going to require energy? Where are we going to get the energy to make it happen? I'm not even going to tell you. You have to watch the next lecture to find out the answer to that. But you know, just looking at the chemical equation for what are we even talking about? Cellular respiration. Totally figure it out where the energy comes from. I'll be right back.