So what you see pictured here is a molecule of adenosine triphosphate, or ATP. Now, it should look somewhat familiar to you because it's very similar to a DNA nucleotide. And let's talk about the components. So first of all, we have right here what we would call a base, and when we talked about DNA nucleotides. So this happens to be an adenine base. We also have a sugar, or a ribose, and then our third component of a DNA nucleotide would be a phosphate group. So that portion there would make an adenine nucleotide. However, as you can see, we have two additional phosphate groups. Here's one, and here's the other. [A total of 3 phosphate groups are present] And so that's why we call this adenosine triphosphate. And one of the reasons that this molecule is so important that I want you to understand is because it is what we call the energy currency of cells.

Now, what do I mean by that? Well, let's say that you want to take a trip. You want to drive somewhere or you need food. You want to make a meal for your family, OK? It requires for any of those things, you're going to need currency or money to do that. You have to put money. You have to give money to the gas station to get gas or the grocery store to get groceries. Well, a cell has to spend currency to do cellular work. A cell may need to produce a protein or move a molecule. Any of those processes are going to require it to spend currency in the form of ATP. OK, so you can think of this as the energy currency of the cell. Now, what I want you to understand about the structure of ATP is it's this last phosphate group. [furthest from the ribose] So the bond here between the second and third phosphate is that is a very important, high

energy bond. Now, we know that energy can't be created or destroyed. So, if there is a great deal of energy in this bond, when the bond is broken, that means there will be a great deal of energy, or a certain amount of energy, released. That is what the cell uses to do cellular work. So, ATP, when we spend money, let's say we have one hundred dollar bill, that would be like our ATP, and we get change back. OK, that would be like cleaving this bond of the third phosphate of ATP. What are you left with when you leave that phosphate? Well, you're left with, or the cell is left with, a molecule of ADP, which means adenosine diphosphate, di standing for the two phosphates. Well, ADP is not nearly as high energy of a molecule. This, the cleavage of this last phosphate, is what allows the cell to use energy to do cellular work. Now, ATP, however, is not meant to be a long-term energy storage.

We store long-term energy storage in the form of fat or glycogen. But ATP is a short-term molecule that allows the cell to do work, and it is constantly being converted back and forth from ATP to ADP in the cell. Now, the cell has processes that it goes through that help to reenergize the ADP molecule back to ATP, and then ATP is used for the cells to do cellular work. So let's talk about how this works. This happens constantly. This is a process that's going on in all of your cells many, many times. So if we have our ATP high-energy molecule, this is the bond that we're talking about that gets broken. [the bond between the 2nd and 3rd phosphate groups] And when that bond is broken or when that phosphate is cleaved off, OK, then we get an individual phosphate released, and this is what allows the cell to do work. What we're left with then is ADP.

OK, where we only have two of the phosphate groups. And this is a low energy molecule, but what the cell does. OK, it takes the ADP and it reenergizes it to a high energy ATP molecule. And the way that it does that is based on the you have to eat food in order to give yourself the raw materials to do that. So, for example, you eat carbohydrates and proteins and fats. Your digestive system breaks those down into individual, individual small molecules. And then in the mitochondria of your cells, your mitochondria go through processes which break the bonds of those nutrient molecules. And the energy in those bonds is used to reenergize ATP. So the food you eat gives provides the energy to continually regenerate the ATP back to ATP in the cell.