Oxidative Phosphorylation: Study with Video Lessons, Practice Problems & Examples

Oxidative phosphorylation synthesizes ATP from ADP using the proton gradient created by the electron transport chain (ETC). This process involves chemiosmosis, where protons diffuse across the membrane, driving ATP synthesis via ATP synthase (complex 5). The ETC comprises complexes 1 to 4, where NADH and FADH₂ donate electrons, ultimately reducing oxygen to water. The theoretical yield of ATP from oxidative phosphorylation is 18 ATP molecules, calculated from 6 NADH (2.5 ATP each) and 2 FADH₂ (1.5 ATP each), though actual yields may vary.

Oxidative Phosphorylation Concept 1

Now, oxidative phosphorylation is the synthesis of ATP from ADP. Here it uses potential energy stored in the proton gradient built by the electron transport chain or ETC. Here we have chemiosmosis, this is just the diffusion of ions across a membrane down their concentration gradient. And here remember, osmosis is the movement from a higher concentration to a lower concentration in this sense. If we take a look here, we have our electron transport chain. Remember the electron transport chain uses complexes 1 to 4. NADH drops off electrons at complex 1. FADH₂ drops them off at complex 2. We're going to say here, Coenzyme Q helps to shuttle those electrons to complex 3. And then cytochrome c will help to shuttle those electrons to complex 4. We're going to have protons being pumped into the inter membrane space in complexes 1, 3, and 4. This is going to cause a gradient to be formed, this is going to help electrons to move down the line with the movement of these protons. O₂ would act as the final electron acceptor generating water. Now on the other side of this, we go to yet another complex, complex 5, also called ATP Synthase. What happens here is that protons then move back into the matrix, and we're going to say, as it does this we're going to phosphorate ADP. So ADP is going to gain an inorganic phosphate to become ATP. And this is where oxidative phosphorylation occurs. Now, here we're going to say that ATP synthase or complex 5, this is just your enzyme complex that facilitates haemostasis and synthesizes ATP. And we're going to say here that proton diffusion through ATP synthase releases energy that drives ADP phosphorylation. So all of this taking of electrons, shuttling them over to the electron transport chain, the whole payoff was getting us to complex 5. Where ATP Synthase comes into play and we start generating a lot of ATP. Now, how much ATP could we generate? We'll find out in the next video.

Oxidative Phosphorylation Concept 2

Now, the total amount of ATP produced by oxidative phosphorylation. Remember, we make 6 NADH's and 2 FADH₂ for 2 cycles of the TCA. And we're going to say here, NADH, we have 2.5 ATP per one NADH, and we have 1.5 ATP for 1 FADH₂. Now we're going to say 6 times 2.5 gives me 15. 2 times 1.5 gives me 3. This gives me a theoretical 18 ATP molecules. Theoretical because that's why we have this asterisk here. Our number may be a little bit higher or a bit lower based on situations. Okay. So here, we have to say 18 is the most realistic number in terms of the amount of ATP that we can generate through oxidative phosphorylation.

Oxidative Phosphorylation Example 1

The diffusion of H⁺ ions from higher concentration to lower concentration occurs at the ATP synthase complex. Note, here it's going on from complex 1 all the way to complex 5, and it's ATP synthase, not ADP synthase. This process requires energy supplied by the formation of ATP. Here, this diffusion is a natural thing, moving from an area of high concentration to an area of low concentration. We have electrons traveling along the way between the different complexes, kind of shuttling this whole thing along. So, no energy is required. It is driven by ATP synthesis. Now, we're going to use natural diffusion to harness that in order to pump H⁺ ions back into the matrix and thereby make ATP. Here, provides energy that facilitates oxidative phosphorylation of ADP. Yes. So H⁺ ions are building up in the intermembrane space, and as we're diffusing from complex 1 all the way to complex 5, they're eventually going to be pumped back into the matrix at complex 5, which is our ATP synthase. We're going to use this pumping of H⁺ back in, harness it in order to do phosphorylation of ADP. This will help to generate ATP. So, here, is the correct answer.

All of the following pump H⁺ ions across the inner membrane of mitochondria except:

• A. Complex I 
• B. Complex II 
• C. Complex III 
• D. Complex IV 
• E. Complex V

Chemiosmotic creation of ATP is driven by which?

• A. ATP Synthase complex.
• B. Oxidative phosphorylation of ADP.
• C. Large quantities of ADP in the mitochondrial matrix.
• D. Potential energy of H⁺ ion concentration gradient created by ETC.

Here’s what students ask on this topic:

What is oxidative phosphorylation and how does it work?

Oxidative phosphorylation is the process of synthesizing ATP from ADP using the proton gradient created by the electron transport chain (ETC). This involves chemiosmosis, where protons diffuse across the mitochondrial membrane, driving ATP synthesis via ATP synthase (complex 5). The ETC consists of complexes 1 to 4, where NADH and FADH₂ donate electrons, ultimately reducing oxygen to water. The energy released from electron transfer pumps protons into the intermembrane space, creating a gradient. Protons then flow back into the matrix through ATP synthase, releasing energy that phosphorylates ADP to ATP.

What is the role of the electron transport chain in oxidative phosphorylation?

The electron transport chain (ETC) plays a crucial role in oxidative phosphorylation by creating a proton gradient across the mitochondrial membrane. It consists of complexes 1 to 4, where NADH and FADH₂ donate electrons. These electrons are transferred through the complexes, releasing energy that pumps protons into the intermembrane space. This creates a proton gradient, which is essential for ATP synthesis. The final electron acceptor is oxygen, which combines with protons to form water. The proton gradient drives protons back into the matrix through ATP synthase, facilitating the phosphorylation of ADP to ATP.

How many ATP molecules are produced in oxidative phosphorylation?

The theoretical yield of ATP from oxidative phosphorylation is 18 ATP molecules. This is calculated from the 6 NADH molecules (each producing 2.5 ATP) and 2 FADH₂ molecules (each producing 1.5 ATP) generated during the TCA cycle. Therefore, 6 NADH × 2.5 ATP/NADH = 15 ATP and 2 FADH₂ × 1.5 ATP/FADH₂ = 3 ATP, giving a total of 18 ATP. However, actual yields may vary due to different cellular conditions.

What is the function of ATP synthase in oxidative phosphorylation?

ATP synthase, also known as complex 5, is an enzyme complex that facilitates the synthesis of ATP during oxidative phosphorylation. It uses the energy from the proton gradient created by the electron transport chain to drive the phosphorylation of ADP to ATP. Protons flow back into the mitochondrial matrix through ATP synthase, releasing energy that is used to add an inorganic phosphate to ADP, forming ATP. This process is essential for producing the majority of ATP in aerobic respiration.

What is chemiosmosis and how does it relate to oxidative phosphorylation?

Chemiosmosis is the movement of ions across a selectively permeable membrane, down their electrochemical gradient. In oxidative phosphorylation, chemiosmosis refers to the diffusion of protons (H⁺) across the mitochondrial membrane. The electron transport chain creates a proton gradient by pumping protons into the intermembrane space. Protons then flow back into the matrix through ATP synthase, releasing energy that drives the phosphorylation of ADP to ATP. Thus, chemiosmosis is a critical step in the production of ATP during oxidative phosphorylation.