Chemiosmosis - Online Tutor, Practice Problems & Exam Prep

Chemiosmosis is the diffusion of hydrogen ions across a semipermeable membrane, driven by a concentration gradient established by the electron transport chain. This process is facilitated by the enzyme ATP synthase, which synthesizes adenosine triphosphate (ATP) through oxidative phosphorylation. The movement of hydrogen ions from the intermembrane space to the mitochondrial matrix powers the phosphorylation of adenosine diphosphate (ADP) into ATP, generating energy crucial for aerobic cellular respiration.

Chemiosmosis

In this video, we're going to discuss chemiosmosis. Recall from our previous lesson videos that the electron transport chain builds a hydrogen ion concentration gradient. That hydrogen ion concentration gradient, built by the electron transport chain, actually has tremendous potential energy. This potential energy can be captured via the process called chemiosmosis. In the word chemiosmosis, you'll find embedded within it the word osmosis, which recall from our previous lesson videos is just referring to the diffusion of water across a semipermeable membrane. When we add the word or the prefix "chemi" in front of it, it's referring to chemicals undergoing osmosis, essentially. Chemiosmosis is the diffusion of chemicals or ions across a semipermeable membrane down their concentration gradient from an area of high concentration to an area of low concentration. Chemiosmosis is facilitated by an enzyme called ATP synthase. When you see ATP synthase, notice that it ends in the letters "ase," and because it ends in "ase," we know that it is an enzyme. It actually synthesizes or builds ATP. ATP Synthase is an enzyme that facilitates chemiosmosis and synthesizes ATP, or energy, for the cell. ATP synthase is ultimately carrying out the process of oxidative phosphorylation, which once again utilizes the electron transport chain, redox reactions to build a hydrogen ion concentration gradient, and chemiosmosis, which takes advantage of that hydrogen ion concentration gradient to power phosphorylation and make lots of ATP.

If we take a look at our example below, we can get a better understanding of chemiosmosis. Notice on the left-hand side what we're showing you is the same image from our previous lesson video of the Electron Transport Chain. The Electron Transport Chain is going to receive electrons from the electron carriers NADH and FADH₂, and these electrons are going to undergo many redox reactions in the electron transport chain, and ultimately end up on oxygen gas which reacts to form water. As these electrons make their way through the electron transport chain they power the movement of hydrogen ions into the intermembrane space. The electron transport chain ultimately builds a hydrogen ion concentration gradient. Here in this video, we're focusing on the process of chemiosmosis, which is really this process over here on the right-hand side. Now that the electron transport chain has built this hydrogen ion concentration gradient that has high hydrogen ion concentration in the intermembrane space and lower hydrogen ion concentration in the mitochondrial matrix, notice that this enzyme embedded in the inner mitochondrial membrane is called an ATP synthase. This blue enzyme, ATP synthase, is going to allow for hydrogen ions to diffuse down their concentration gradient in this direction, and that diffusion of the ions down their concentration gradient is ultimately going to power the phosphorylation of ADP into ATP. Ultimately, this ATP is going to be created by the process of oxidative phosphorylation. Notice that this ATP being made is created by oxidative phosphorylation, and recall that oxidative phosphorylation is going to create the vast majority of the ATP associated with aerobic cellular respiration. Ultimately, oxidative phosphorylation is the cumulative sum of the electron transport chain building the hydrogen ion concentration gradient, and chemiosmosis, which utilizes hydrogen ions diffusing across the membrane, and that ultimately is going to power oxidative phosphorylation. This here concludes our introduction to chemiosmosis, and we'll be able to get some practice applying the concepts that we've learned here as we move forward in our course. So, I'll see you all in our next video.

Chemiosmotic creation of ATP is driven by:

a) Phosphate transfer through the plasma membrane.

b) Potential energy of the H⁺ concentration gradient created by the electron transport chain.

c) Substrate-level phosphorylation in the mitochondrial matrix.

d) Large quantities of ADP in the mitochondrial matrix.

• A. Phosphate transfer through the plasma membrane.
• B. Potential energy of the H+ concentration gradient created by the electron transport chain.
• C. Substrate-level phosphorylation in the mitochondrial matrix.
• D. Large quantities of ADP in the mitochondrial matrix.

The electron transport chain pumps H⁺ ions into which location of the mitochondria?

a) Mitochondrial intermembrane space. 

b) Mitochondrial matrix.

c)  Mitochondrial inner membrane.

d) The H⁺ ions are pumped out of the mitochondria.

• A. Mitochondrial intermembrane space.
• B. Mitochondrial inner membrane.
• C. Mitochondrial matrix.
• D. The H⁺ ions are pumped out of the mitochondria.

Here’s what students ask on this topic:

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

Chemiosmosis is the diffusion of hydrogen ions (H⁺) across a semipermeable membrane, driven by a concentration gradient established by the electron transport chain. This process is facilitated by the enzyme ATP synthase, which synthesizes adenosine triphosphate (ATP) through oxidative phosphorylation. The movement of H⁺ from high to low concentration powers the phosphorylation of adenosine diphosphate (ADP) into ATP. This is crucial for aerobic cellular respiration, as it generates the majority of the cell's ATP, providing the energy necessary for various cellular functions.

How does the electron transport chain create a hydrogen ion gradient?

The electron transport chain (ETC) creates a hydrogen ion (H⁺) gradient by transferring electrons through a series of protein complexes embedded in the inner mitochondrial membrane. As electrons move through these complexes, energy is released and used to pump H⁺ from the mitochondrial matrix into the intermembrane space. This creates a high concentration of H⁺ in the intermembrane space and a low concentration in the matrix, establishing a gradient. This gradient is essential for chemiosmosis, as the flow of H⁺ back into the matrix through ATP synthase drives ATP production.

What role does ATP synthase play in chemiosmosis?

ATP synthase is a crucial enzyme in chemiosmosis that facilitates the production of ATP. It is embedded in the inner mitochondrial membrane and allows hydrogen ions (H⁺) to diffuse down their concentration gradient from the intermembrane space into the mitochondrial matrix. The flow of H⁺ through ATP synthase provides the energy needed to phosphorylate adenosine diphosphate (ADP) into adenosine triphosphate (ATP). This process, known as oxidative phosphorylation, generates the majority of ATP during aerobic cellular respiration.

Why is chemiosmosis important for cellular respiration?

Chemiosmosis is vital for cellular respiration because it is the primary mechanism by which ATP is produced in aerobic organisms. During cellular respiration, the electron transport chain creates a hydrogen ion (H⁺) gradient across the inner mitochondrial membrane. Chemiosmosis utilizes this gradient to drive the synthesis of ATP via ATP synthase. The ATP produced is essential for various cellular processes, including muscle contraction, protein synthesis, and cell division. Without chemiosmosis, cells would not be able to efficiently generate the energy required for survival and function.

How does oxidative phosphorylation differ from substrate-level phosphorylation?

Oxidative phosphorylation and substrate-level phosphorylation are two methods of ATP production. Oxidative phosphorylation occurs in the mitochondria and involves the electron transport chain and chemiosmosis. It relies on a hydrogen ion (H⁺) gradient and ATP synthase to produce ATP. In contrast, substrate-level phosphorylation occurs directly in the cytoplasm or mitochondrial matrix during glycolysis and the Krebs cycle. It involves the direct transfer of a phosphate group from a substrate molecule to adenosine diphosphate (ADP) to form ATP. Oxidative phosphorylation generates more ATP compared to substrate-level phosphorylation.