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 cellular functions. Understanding chemiosmosis is essential for grasping aerobic cellular respiration and energy production in cells.

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. The hydrogen ion concentration gradient that is 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 just referring to chemicals that are 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 going to be 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 the letters "ase", we know that it is an enzyme. It is an enzyme that synthesizes or builds ATP. ATP Synthase is an enzyme that facilitates chemiosmosis and synthesizes ATP or energy for the cell. The 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 once again lots of ATP.

If we take a look at our example down below we can get a better understanding of chemiosmosis. Notice over here 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 is going to build 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 with 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 the ATP being made is created by oxidative phosphorylation, and recall oxidative phosphorylation is going to create the vast majority of the ATP associated with aerobic cellular respiration. Ultimately, oxidative phosphorylation is going forward be 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 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⁺ ions from the intermembrane space to the mitochondrial matrix powers the phosphorylation of adenosine diphosphate (ADP) into ATP. This ATP is crucial for cellular functions, making chemiosmosis a key component of aerobic cellular respiration and energy production in cells.

What role does the electron transport chain play in chemiosmosis?

The electron transport chain (ETC) plays a crucial role in chemiosmosis by establishing a hydrogen ion (H⁺) concentration gradient across the inner mitochondrial membrane. As electrons are transferred through a series of redox reactions in the ETC, energy is released, which is used to pump H⁺ ions from the mitochondrial matrix into the intermembrane space. This creates a high concentration of H⁺ ions in the intermembrane space and a low concentration in the matrix. The resulting gradient has tremendous potential energy, which is harnessed by ATP synthase during chemiosmosis to produce ATP.

How does ATP synthase facilitate the process of chemiosmosis?

ATP synthase is an enzyme embedded in the inner mitochondrial membrane that facilitates chemiosmosis. It allows hydrogen ions (H⁺) to diffuse down their concentration gradient from the intermembrane space into the mitochondrial matrix. As H⁺ ions pass through ATP synthase, the enzyme harnesses the energy released from this movement to catalyze the phosphorylation of adenosine diphosphate (ADP) into adenosine triphosphate (ATP). This process is a key part of oxidative phosphorylation, which generates the majority of ATP during aerobic cellular respiration.

What is the significance of the hydrogen ion concentration gradient in chemiosmosis?

The hydrogen ion (H⁺) concentration gradient is essential for chemiosmosis because it represents a form of potential energy. This gradient is established by the electron transport chain, which pumps H⁺ ions from the mitochondrial matrix into the intermembrane space. The high concentration of H⁺ ions in the intermembrane space and the low concentration in the matrix create a strong electrochemical gradient. During chemiosmosis, H⁺ ions flow back into the matrix through ATP synthase, and the energy released from this movement is used to synthesize ATP from ADP and inorganic phosphate (P_i).

What is oxidative phosphorylation and how is it related to chemiosmosis?

Oxidative phosphorylation is the process by which ATP is produced as a result of the transfer of electrons from NADH and FADH₂ to oxygen via the electron transport chain (ETC). This process involves two main components: the ETC and chemiosmosis. The ETC creates a hydrogen ion (H⁺) concentration gradient across the inner mitochondrial membrane. Chemiosmosis then utilizes this gradient, allowing H⁺ ions to flow back into the mitochondrial matrix through ATP synthase. The energy released during this flow drives the phosphorylation of adenosine diphosphate (ADP) to adenosine triphosphate (ATP), making oxidative phosphorylation a critical step in cellular respiration.