Types of Phosphorylation: Study with Video Lessons, Practice Problems & Examples

Aerobic cellular respiration generates ATP through two main types of phosphorylation: substrate-level phosphorylation and oxidative phosphorylation. Substrate-level phosphorylation directly transfers a phosphate group to ADP using an enzyme, producing a small amount of ATP during glycolysis and the Krebs cycle. In contrast, oxidative phosphorylation, occurring in the electron transport chain and chemiosmosis, utilizes energy from redox reactions to create a significant amount of ATP, representing the majority produced in aerobic respiration. Understanding these processes is crucial for grasping cellular energy production.

Types of Phosphorylation

So recall from our previous lesson videos that the whole point of aerobic cellular respiration is to make a lot of ATP or energy for the cell. But really during aerobic cellular respiration, the ATP that is being made can actually be made via 2 different types of phosphorylation. And so here in this video, we're introducing the types of phosphorylation that occur during aerobic cellular respiration. And those 2 different types of phosphorylation that create ATP during aerobic cellular respiration are number 1, substrate level phosphorylation, and number 2, oxidative phosphorylation. And so in our next lesson video, we'll introduce substrate level phosphorylation, and then later in another video, we'll introduce oxidative phosphorylation. So I'll see you all in our next lesson video where we introduce substrate level phosphorylation.

Substrate-Level Phosphorylation

In this video, we're going to introduce substrate level phosphorylation, which is one of the types of phosphorylation used to make ATP during aerobic cellular respiration. Substrate level phosphorylation uses an enzyme and a substrate in order to directly transfer a phosphate group to ADP, creating ATP or energy for the cell. If we take a look at our image over here on the left-hand side, we can get a better idea of substrate level phosphorylation. Notice here we have the enzyme and the substrate, and the substrate is phosphorylated. It has a phosphate group on the substrate, and the enzyme is going to catalyze the transfer of this phosphate group to ADP, the low energy form, and that's ultimately going to create ATP, the high energy form. This is substrate level phosphorylation, just an enzyme catalyzing the transfer of a phosphate group to ADP creating ATP.

Now, substrate level phosphorylation is specifically used to make a very small amount of ATP during glycolysis and the Krebs Cycle. Notice that, over here on the right-hand side, what we're showing you are the four stages of aerobic cellular respiration: glycolysis, pyruvate oxidation, the Krebs cycle, and the electron transport chain in chemiosmosis. Notice specifically that substrate level phosphorylation is going to occur during glycolysis and during the Krebs cycle, but it does not occur during pyruvate oxidation or during the electron transport chain. Ultimately, what we can see down below here is that glycolysis and the Krebs cycle both produce a very small amount of ATP via substrate level phosphorylation.

What we'll learn later in our course when we talk more about glycolysis and the Krebs cycle is that both glycolysis and the Krebs cycle only create 2 ATP each. That is not a lot of ATP in comparison to the next type of phosphorylation that we're going to talk about in our next lesson video. This here concludes our introduction to substrate level phosphorylation and how it only creates a small amount of ATP in the Krebs cycle. In our next lesson video, we'll get to talk about oxidative phosphorylation. So I'll see you all there.

Oxidative Phosphorylation

In this video, we're going to introduce oxidative phosphorylation, which is the second type of phosphorylation used to make ATP during aerobic cellular respiration. Now in this video of oxidative phosphorylation, what we're going to learn is that oxidative phosphorylation occurs in a 2-step process. The first step is going to be the electron transport chain or the ETC for short, and the second step is going to be Chemiosmosis. Now in this video, we're not going to talk a lot of details about the Electron Transport Chain a lot a lot more details about both the electron transport chain and chemiosmosis, so keep that in mind. And in this video, really there's only a few takeaways that you should get from this video. And so I'll make sure to make those few takeaways very clear by the end of the video.

So oxidative phosphorylation, as its name implies with oxidative here, is going to use energy from oxidation-reduction reactions or, in short, redox reactions. And these redox reactions are going to take place in the electron transport chain or the ETC, which once again we'll talk more details about the electron transport chain or the ETC later in our course in a different video. But ultimately, oxidative phosphorylation is going to use the energy from redox reactions that take place in the electron transport chain, and it's going to use that energy of the redox reactions to phosphorylate ADP and create a lot of ATP. And so what we'll learn later in our course is that the electron transport chain is going to build a hydrogen ion concentration gradient or an h plus concentration gradient. And the h⁺ concentration gradient is going to be used to make a large amount of ATP. And really, this is the biggest takeaway of this video. That oxidative phosphorylation is going to make a large amount of ATP and the vast majority of ATP that's associated with aerobic cellular respiration.

Now once again, the electron transport chain is just part of oxidative phosphorylation because oxidative phosphorylation consists of both the electron transport chain and this other process called chemiosmosis. And again, we're going to talk about more details about the electron transport chain and chemiosmosis later in our course in a different video. For now here, we're just briefly introducing these. And chemiosmosis is defined as the diffusion of ions, more specifically hydrogen ions, across a membrane down their concentration gradient from high to low concentration. And so technically, the electron transport chain and chemiosmosis combined allow for the process of oxidative phosphorylation, and we'll be able to see that down below in our image.

So over here on the left-hand side of the image, notice that we're showing you a very complicated image of the electron transport chain and chemiosmosis. So we're not going to explain this image here in this video. Again, we'll talk about the electron transport chain and chemiosmosis in more detail in a different video later in our course.

For now here, this is just a foreshadowing image, and together the electron transport chain, which builds a hydrogen ion concentration gradient, and chemiosmosis, which utilizes the concentration gradient to phosphorylate ADP and make a lot of ATP. These two processes combined, the ETC, and chemiosmosis allow for oxidative phosphorylation. And so this whole stage that you see here, this whole image that you see here, is going to take place in the last stage of the aerobic cellular respiration. And so here on the right-hand side, notice that we're showing you the 4 stages of aerobic cellular respiration. And notice that the first three stages, glycolysis, pyruvate oxidation, and the Krebs cycle are not involved directly with oxidative phosphorylation. And so the only stage that's directly involved with oxidative phosphorylation is this fourth and final stage, which actually consists of the electron transport chain and chemiosmosis. Two processes that we'll talk a lot more about later in our course.

But one of the most significant takeaways that you should get from this video is that together the electron transport chain and chemiosmosis allow for oxidative phosphorylation. And so ultimately, the electron transport chain in chemiosmosis, or in other words, oxidative phosphorylation, is what produces a large amount of ATP. And once again, this is probably the most substantial takeaway of this video. That oxidative phosphorylation is going to generate a large amount of ATP. And once again, what we have is another image down below to just clarify the idea that oxidative phosphorylation consists of both the electron transport chain or the ETC and chemiosmosis together. And so if you have the electron transport chain and chemiosmosis, then the cell is able to perform oxidative phosphorylation.

And once again, we're going to talk a lot more details about the electron transport chain and chemiosmosis later in our course, and we'll talk more details about oxidative phosphorylation later in our course as well. But for now, the most significant takeaway that you should get from this video is that oxidative phosphorylation is going to occur in the fourth and final stage of aerobic cellular respiration, and it's going to create a large amount of ATP, the vast majority of ATP that's associated with aerobic cellular respiration. And really those are the two most significant takeaways of this video. And so once again, this here concludes our brief introduction to oxidative phosphorylation, and we'll talk a lot more about this much later in our course. And we'll be able to get some practice applying the concepts that we've learned as we move forward. So I'll see you all in our next video.

Substrate-level phosphorylation is utilized to create ATP in which steps of aerobic cellular respiration?

a) Electron Transport Chain and Chemiosmosis.

b) Glycolysis and Pyruvate Oxidation.

c) Pyruvate Oxidation and Krebs cycle.

d) Glycolysis and Krebs cycle.

• A. Electron Transport Chain and Chemiosmosis.
• B. Glycolysis and Pyruvate Oxidation.
• C. Pyruvate Oxidation and Krebs cycle.
• D. Glycolysis and Krebs cycle.

Answer: (D)

Which type of phosphorylation synthesizes ATP using an enzyme that transfers a phosphate group to ADP?

a) Adaptive Phosphorylation. 

b) Oxidative Phosphorylation. 

c) Substrate-level Phosphorylation.

d) Product-level Phosphorylation.

• A. Adaptive Phosphorylation.
• B. Oxidative Phosphorylation.
• C. Substrate-level Phosphorylation.
• D. Product-level Phosphorylation.

Answer: (C)

The largest amount of ATP made by cellular respiration is created by the process of ______________, in the _____________ steps of aerobic cellular respiration.

a) Substrate-level phosphorylation; first.

b) Oxidative phosphorylation; first.

c) Oxidative phosphorylation; final.

d) Substrate-level phosphorylation; final.

• A. Substrate-level phosphorylation; first.
• B. Oxidative phosphorylation; first.
• C. Oxidative phosphorylation; final.
• D. Substrate-level phosphorylation; final.

Answer: (C)

Here’s what students ask on this topic:

What are the two main types of phosphorylation in aerobic cellular respiration?

The two main types of phosphorylation in aerobic cellular respiration are substrate-level phosphorylation and oxidative phosphorylation. Substrate-level phosphorylation involves the direct transfer of a phosphate group to ADP using an enzyme, producing a small amount of ATP during glycolysis and the Krebs cycle. On the other hand, oxidative phosphorylation occurs in the electron transport chain and chemiosmosis, utilizing energy from redox reactions to create a significant amount of ATP. This process represents the majority of ATP produced in aerobic respiration. Understanding these processes is crucial for grasping cellular energy production.

How does substrate-level phosphorylation differ from oxidative phosphorylation?

Substrate-level phosphorylation differs from oxidative phosphorylation in several ways. Substrate-level phosphorylation directly transfers a phosphate group to ADP using an enzyme and a phosphorylated substrate, producing a small amount of ATP during glycolysis and the Krebs cycle. In contrast, oxidative phosphorylation occurs in the electron transport chain and chemiosmosis, where energy from redox reactions is used to create a proton gradient. This gradient drives the synthesis of a large amount of ATP. Thus, while substrate-level phosphorylation produces ATP directly and in small quantities, oxidative phosphorylation generates the majority of ATP through a more complex, indirect process.

What role does the electron transport chain play in oxidative phosphorylation?

The electron transport chain (ETC) plays a crucial role in oxidative phosphorylation by facilitating redox reactions that transfer electrons through a series of protein complexes. As electrons move through the ETC, energy is released and used to pump hydrogen ions (H⁺) across the inner mitochondrial membrane, creating a concentration gradient. This gradient, known as the proton motive force, is essential for the second step of oxidative phosphorylation, chemiosmosis. During chemiosmosis, the flow of H⁺ back into the mitochondrial matrix through ATP synthase drives the phosphorylation of ADP to ATP, producing a large amount of ATP.

During which stages of aerobic cellular respiration does substrate-level phosphorylation occur?

Substrate-level phosphorylation occurs during two specific stages of aerobic cellular respiration: glycolysis and the Krebs cycle. In glycolysis, it produces a small amount of ATP by directly transferring a phosphate group from a phosphorylated substrate to ADP. Similarly, in the Krebs cycle, substrate-level phosphorylation generates ATP through a direct enzymatic transfer of a phosphate group. These processes collectively produce a relatively small amount of ATP compared to the large amount generated by oxidative phosphorylation in the electron transport chain and chemiosmosis.

What is chemiosmosis and how does it contribute to ATP production?

Chemiosmosis is the process by which ions, specifically hydrogen ions (H⁺), diffuse across a membrane down their concentration gradient. In the context of oxidative phosphorylation, chemiosmosis occurs in the inner mitochondrial membrane. The electron transport chain creates a high concentration of H⁺ in the intermembrane space. These ions then flow back into the mitochondrial matrix through ATP synthase, a protein complex that uses the energy from this flow to phosphorylate ADP, forming ATP. This process is crucial for producing the majority of ATP during aerobic cellular respiration.