ATP - Online Tutor, Practice Problems & Exam Prep

ATP

In this video, we're going to begin our lesson on ATP. Now, recall from our previous lesson videos that ATP is really just an abbreviation for a molecule called adenosine triphosphate, where the a in ATP is for the a in adenosine, the t in ATP is for the t in tri, and the p in ATP is for the p in phosphate. Adenosine Triphosphate or ATP is a high-energy molecule that's used to power cellular activities. If the cell has a lot of ATP, then the cell has a lot of energy. But if the cell has a little bit of ATP, then the cell only has a little bit of energy. There are only three primary components of an ATP molecule. As its name implies with the triphosphate part, tri meaning three, there are a chain of three phosphate groups in an ATP molecule. The adenosine part of ATP refers to a molecule that has two components: a pentose sugar and an adenine nitrogenous base. Let's take a look at our image down below on the left-hand side to get a better understanding of the three components of adenosine triphosphate or ATP. Again, the triphosphate part refers to a chain of three phosphate groups that you see here, 1, 2, and 3. We can go ahead and label these as phosphate groups, and there are indeed three phosphate groups on an ATP molecule. The adenosine portion of ATP refers to both this sugar and this nitrogenous base. You can see that there is a pentose sugar here, which is this portion, and also a nitrogenous base here, which is the nitrogenous base of adenine. Together the adenine nitrogenous base and the pentose sugar make up the adenosine portion of ATP. It's also important to note that ATP is a high-energy molecule, but the way that cells extract energy from ATP is through a process called ATP hydrolysis.

ATP hydrolysis is the process of breaking bonds between phosphate groups in an ATP molecule, generating chemical energy that can be used by the cell and producing adenosine diphosphate (ADP) where the d stands for di, meaning it has only two phosphate groups. In some scenarios, ADP can also be hydrolyzed to form AMP (adenosine monophosphate), and the m is referring to mono, meaning just one phosphate. Let's take a look at our image down below on the right-hand side to get a better understanding of ATP and ADP hydrolysis. You can notice that at the very top, we're starting with an ATP molecule. The nitrogenous base and the pentose sugar are represented in green, and the three phosphate groups are right here, 1, 2, and 3. ATP can be represented by this symbol right here, and we'll be doing that throughout the rest of our course. When we hydrolyze ATP using water to break the bonds between phosphate groups, one of the phosphate groups is released along with energy. This energy can be used to power other chemical reactions and cellular activities. The molecule that remains only has two phosphate groups, making it ADP since the d stands for diphosphate. Di is a root that means only two phosphates, one here and the other here. The third one is released or attached to some other molecule, and in the process, a lot of energy is released. In certain scenarios, ADP can be hydrolyzed, releasing a phosphate group and energy, forming an AMP molecule. The m in AMP stands for mono, meaning only one phosphate group. The hydrolysis leads to the release of energy, which is used to power chemical reactions. This concludes our brief introduction to ATP, and we'll be able to get some more practice applying these concepts and learning more about ATP as we move forward in our course. So I'll see you all in our next video.

Which of the following statements is true?

• A. ADP contains more potential energy than ATP.
• B. Following hydrolysis, ATP can give off one phosphate group and usable energy, whereas ADP cannot.
• C. The energy produced by ATP comes from the breaking of the bond between two phosphate groups.
• D. AMP and ADP contain the same amount of potential energy.

Which of the following is the most correct interpretation of the figure?

• A. Energy from food sources can be used directly for performing cellular work.
• B. ADP + Pi are a set of molecules that store energy.
• C. ATP is a molecule that acts as an intermediary to store energy for cellular work.
• D. Pi acts as a shuttle molecule to move energy from ATP to ADP.

Energy Coupling

In this video, we're going to introduce energy coupling. Energy coupling is basically when energy released by an exergonic reaction is used to power or drive an endergonic reaction that requires an energy input. Recall from our last lesson video that ATP hydrolysis is a reaction that is an exergonic reaction, and so ATP hydrolysis releases energy into the environment. ATP hydrolysis is usually what's going to be coupled to endergonic reactions because the released energy from ATP hydrolysis is used to provide the energy input that those endergonic reactions need to proceed. Let's take a look at our image down below to get a better feel for energy coupling. Notice on the left-hand side over here, we show you this pizza, and that's because a lot of the energy that we get is from the foods that we end up eating. When we eat pizza, the pizza is going to have all different kinds of molecules in it. It's going to have carbohydrates, proteins, lipids, and more. Those molecules that are in the foods that we eat end up providing energy for our bodies. Our bodies are going to perform exergonic reactions to essentially break down the foods. You can see that here we are showing you the reaction for exergonic reactions. They start with large food molecules and break them down into smaller components, ultimately allowing for converting the energy that's in food into chemical energy in the form of ATP. This energy is going to be used to make ATP. Once ATP is made, the cell can perform ATP hydrolysis. Here in this box, you can see the reactants that are needed for ATP hydrolysis to occur. Of course, they're going to need ATP for ATP hydrolysis to occur and also it's going to need water. ATP hydrolysis is going to be an exergonic reaction, and when ATP is hydrolyzed, it is going to release a lot of energy as we can see here, being released, and also, it's going to end up creating a phosphate group as well as ADP. But this energy that is released is really important and this is where the energy coupling comes into play because ATP hydrolysis is an exergonic reaction that releases energy, and this energy is going to be used directly to provide the energy input that's needed for an endergonic reaction, like what you see here, using smaller molecules to build larger molecules. Using ATP, the energy released by ATP in order to create kinetic energy such as when you're riding your bicycle, the energy that's essentially being used is coming from ATP hydrolysis. Again, ATP hydrolysis is going to create ADP and a phosphate group, and these are the reactants that are needed for ATP formation or ATP production. You can see that ATP production, the energy that's going to be added into ADP, is going to come directly from the energy in the foods that we eat. Ultimately here, you can see that with energy coupling, the movements that we have, the kinetic energy that we need to ride a bike is ultimately derived directly by ATP hydrolysis, and ATP hydrolysis has ATP whose energy comes directly from the foods that we eat, breaking down the foods that we eat. It's the foods that we eat that ultimately can be traced to providing the energy for our movements and muscle contractions. Ultimately here, exergonic reactions are used, in order to power endergonic reactions and this is the idea of energy coupling. This concludes our introduction to energy coupling and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.

How does ATP participate in energy-coupling reactions?

• A. Hydrolysis of ATP fuels endergonic reactions.
• B. Hydrolysis of ADP fuels endergonic reactions.
• C. Synthesis of ATP fuels exergonic reactions.
• D. Synthesis of ADP fuels exergonic reactions.

Phosphorylation

In this video, we're going to introduce Phosphorylation. Phosphorylation refers to the transfer of a phosphate group from ATP to another molecule in order to provide energy. Phosphorylation by ATP hydrolysis can have a wide variety of effects, including activating a target molecule so that it's capable of reacting, as well as changing the conformation of a target protein. Notice in the image below on the left hand side, we're showing a glucose molecule here as a green hexagon. This glucose molecule is shown in its inactive form, meaning it's not able to react. However, after ATP hydrolysis and phosphorylation of the glucose molecule, where phosphorylation is just the transfer of a phosphate group from ATP to another molecule, the situation changes. Adenosine triphosphate (ATP) has three phosphates, whereas adenosine diphosphate (ADP) only has two phosphates. Thus, the third phosphate was transferred over to glucose. This phosphorylated form of glucose is the active form, able to go on to react.

Phosphorylation does not always lead to activation of a target molecule; this is just an example of what phosphorylation can lead to. Remember, phosphorylation leads to a wide variety of effects. In some scenarios, phosphorylation will lead to activation, but in other scenarios, phosphorylation could lead to inactivation as well. The idea here is that phosphorylation can have a wide variety of effects.

On the right hand side, we're focusing on a protein represented by a red circle. After ATP hydrolysis and phosphorylation of the protein, the protein takes on a completely different conformation. It changes its shape, its structure, and therefore, likely its function as well. You can see the phosphorylated protein here has an altered conformation. This concludes our introduction to phosphorylation and how ATP is usually going to be the source of the phosphate group in phosphorylation. Phosphorylation can lead to a wide variety of effects including activating a target to react and changing the conformation of a target protein.

This concludes our lesson and I'll see you guys in our next video.