ATP - Online Tutor, Practice Problems & Exam Prep

Adenosine triphosphate (ATP) is a high-energy molecule essential for cellular activities, consisting of three phosphate groups, a pentose sugar, and an adenine base. Energy is released through ATP hydrolysis, converting ATP to adenosine diphosphate (ADP) and a phosphate group. This energy coupling drives endergonic reactions, such as muscle contractions. Phosphorylation, the transfer of a phosphate group from ATP, can activate or alter target molecules, influencing their reactivity and function. Understanding these processes is crucial for grasping cellular energy dynamics and metabolic pathways.

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. And so 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 is referring to a molecule that actually has two components: a pentose sugar and an adenine nitrogenous base. Let's take a look at our image down below over here on the left-hand side to get a better understanding of the three components of adenosine triphosphate or ATP. The triphosphate part is referring 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, in fact, three phosphate groups on an ATP molecule. The adenosine portion of ATP is actually referring to both this sugar as well as this nitrogenous base. You can see that there is a pentose sugar here, which is this portion right here, and there's also a nitrogenous base right here, which is actually the nitrogenous base of adenine. Together, the adenine nitrogenous base and the pentose sugar here make up the adenosine portion of ATP. ATP is a high-energy molecule, but the way that cells extract the 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 that ends up generating chemical energy that can be used by the cell as well as ADP, or adenosine diphosphate, where the 'd' here stands for 'di,' meaning that it only has two phosphate groups. In some scenarios, ADP can also be hydrolyzed to form AMP, and the 'm' here is referring to 'mono,' adenosine monophosphate, and 'mono' is a prefix that means just one phosphate. Let's take a look at our image down below over here on the right-hand side to get a better understanding of ATP and ADP hydrolysis. Notice that at the very top here, we're starting with an ATP molecule. This is another representation of the base and the nitrogenous base and the pentose sugar represented right here in green. Then the three phosphate groups are right here, 1, 2, and 3. We can also represent ATP by this symbol right here, and we'll be doing that a lot throughout the rest of our course, representing ATP as just this symbol right here. If we take ATP and hydrolyze it, 'hydro' is the prefix for water, 'lysis' is the prefix for breaking down. Using water to break down ATP, you can see that water can be used to break the bonds between phosphate groups, the process of breaking the bonds between phosphate groups. When we break off this bond right here between the phosphate group using water, ultimately, what we end up getting is one of the phosphate groups is released and also energy is released. That energy can be used to power other chemical reactions and used to power other cellular activities. The molecule that remains only has two phosphate groups here, and so this molecule is now ADP, since the 'd' here stands for diphosphate. 'Di' is a root that means only two phosphates, one right here and the other one right there. The third one is released or attached to some other molecule, and in the process, a lot of energy is released. Again, in some scenarios, ADP, this molecule here, can also be hydrolyzed, releasing, as you can see the water here coming in to break this bond and that will release the phosphate group and also release energy as well. The AMP molecule is going to be made here. Again, the 'M' in AMP is for mono, and mono means only one phosphate group. You can see how the hydrolysis here is going to lead to the release of energy, and the release of energy is really what's going to be used to power chemical reactions. This here 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.

• 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 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're showing 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're showing you the reaction for exergonic reactions. They start with large food molecules and they 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.

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. 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 and that exergonic reaction releases energy, and this energy is going to be used directly to provide the energy input that's needed for an endergonic reaction. Using smaller molecules to build larger ones when you're riding your bicycle, the energy that's being used is coming from ATP hydrolysis.

Now again, ATP hydrolysis is going to create ADP and a phosphate group, and these are really the reactants that are needed for ATP formation. You can see that ATP production energy that's going to be added into ADP is going to come directly from the energy in foods that we eat. Ultimately, with energy coupling, the movements that we have, the kinetic energy that we need to ride a bike is ultimately going to be 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. Exergonic reactions are used to power endergonic reactions, and this is the idea of energy coupling.

This here 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. 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.

• 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 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 left-hand image, we're showing a glucose molecule here as the 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 the transfer of a phosphate group from ATP to another molecule—notice that this phosphorylated form of glucose is the active form of glucose, which would be able to react. Now, phosphorylation does not always lead to the activation of a target molecule. This is just one example of what phosphorylation can lead to. Remember, phosphorylation can have a wide variety of effects. In some scenarios, phosphorylation will lead to activation, but in other scenarios, it could lead to inactivation as well.

On the right-hand side, we are focusing on a protein. This red circle represents a protein. Notice that after ATP hydrolysis and phosphorylation of the protein, the protein takes on a completely different conformation. It changes its shape, 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 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.

Here’s what students ask on this topic:

What is ATP and why is it important for cellular activities?

ATP, or adenosine triphosphate, is a high-energy molecule crucial for cellular activities. It consists of three phosphate groups, a pentose sugar, and an adenine base. ATP serves as the primary energy currency of the cell. When ATP is hydrolyzed to ADP (adenosine diphosphate) and a phosphate group, energy is released. This energy is used to power various cellular processes, such as muscle contractions, active transport, and biochemical reactions. Without ATP, cells would not have the energy required to maintain their functions, leading to cellular and organismal failure.

How does ATP hydrolysis release energy?

ATP hydrolysis releases energy through the breaking of the bond between the second and third phosphate groups. This process involves the addition of a water molecule (hydrolysis), which cleaves the bond, resulting in the formation of ADP (adenosine diphosphate) and an inorganic phosphate (Pi). The chemical equation for ATP hydrolysis is:

${\mathrm{ATP}}_{}+H_{2}O\to {\mathrm{ADP}}_{}+P_i+\mathrm{energy}$

The energy released is used to drive various cellular processes, making ATP hydrolysis a key reaction in cellular metabolism.

What is the role of ATP in energy coupling?

In energy coupling, ATP plays a crucial role by linking exergonic and endergonic reactions. Exergonic reactions release energy, while endergonic reactions require an energy input. ATP hydrolysis is an exergonic reaction that releases energy, which can then be used to drive endergonic reactions. For example, the energy released from ATP hydrolysis can be used to synthesize macromolecules, transport substances across cell membranes, and perform mechanical work like muscle contractions. This coupling ensures that energy released from catabolic processes is efficiently used for anabolic processes, maintaining cellular function and homeostasis.

What is phosphorylation and how does it affect target molecules?

Phosphorylation is the process of transferring a phosphate group from ATP to another molecule. This transfer can activate or deactivate the target molecule, alter its conformation, or change its function. For instance, phosphorylation can activate enzymes, making them capable of catalyzing reactions. It can also change the shape of proteins, affecting their activity and interactions. The versatility of phosphorylation allows it to regulate various cellular processes, including signal transduction, metabolism, and cell cycle progression. Thus, phosphorylation is a key mechanism for controlling cellular activities and responses.

What are the components of an ATP molecule?

An ATP molecule consists of three main components: three phosphate groups, a pentose sugar (ribose), and an adenine nitrogenous base. The three phosphate groups are linked in a chain, with high-energy bonds between them. The pentose sugar, ribose, forms the backbone of the molecule, and the adenine base is attached to the ribose. The structure of ATP allows it to store and release energy efficiently, making it an essential molecule for cellular energy transfer.