Cellular Respiration: 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 high to low concentration powers the phosphorylation of adenosine diphosphate (ADP) into ATP, generating energy crucial for aerobic cellular respiration. Understanding chemiosmosis is essential for grasping 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. That 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 refers to the diffusion of water across a semi-permeable membrane, as discussed in our previous lessons.

When we add the prefix chemi in front of osmosis, it refers 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," indicating that it is an enzyme. It is an enzyme that synthesizes or builds ATP.

ATP synthase facilitates chemiosmosis and synthesizes ATP or energy for the cell. ATP synthase is ultimately carrying out the process of Oxidative Phosphorylation, which again utilizes the electron transport chain and redox reactions to build a hydrogen ion concentration gradient. Chemiosmosis takes advantage of this hydrogen ion concentration gradient to power phosphorylation and make lots of ATP. If we look at our example below, we can get a better understanding of chemiosmosis. Notice over here on the left-hand side, we're showing you the same image from our previous lesson video of the Electron Transport Chain. The Electron Transport Chain receives electrons from the electron carriers NADH and FADH₂, and these electrons 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. In this video, we're focusing on the process of chemiosmosis which is the 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 ATP synthase. This blue enzyme, ATP synthase, allows for hydrogen ions to diffuse down their concentration gradients in this direction, and that diffusion of the ions down their concentration gradient ultimately powers 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 that oxidative phosphorylation is going to create the vast majority of the ATP associated with aerobic cellular respiration. 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 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.

The electron transport chain pumps H⁺ ions into which location 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 in cellular respiration?

Chemiosmosis in cellular respiration refers to the movement 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 an area of high concentration in the intermembrane space to an area of low concentration in the mitochondrial matrix powers the phosphorylation of adenosine diphosphate (ADP) into ATP, generating energy crucial for aerobic cellular respiration.

How does the electron transport chain contribute to chemiosmosis?

The electron transport chain (ETC) contributes to chemiosmosis by creating 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⁺ 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. The resulting electrochemical gradient, known as the proton motive force, drives H⁺ back into the matrix through ATP synthase, facilitating the production of ATP.

What role does ATP synthase play in chemiosmosis?

ATP synthase plays a crucial role in chemiosmosis by facilitating the diffusion of hydrogen ions (H⁺) across the inner mitochondrial membrane. As H⁺ ions flow down their concentration gradient from the intermembrane space into the mitochondrial matrix, they pass through ATP synthase. This flow of ions provides the energy needed for ATP synthase to catalyze the phosphorylation of adenosine diphosphate (ADP) into adenosine triphosphate (ATP). Thus, ATP synthase is essential for converting the potential energy of the H⁺ gradient into the chemical energy stored in ATP.

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

The hydrogen ion (H⁺) concentration gradient is significant in chemiosmosis because it represents a form of potential energy that can be harnessed to produce ATP. This gradient is established by the electron transport chain, which pumps H⁺ ions from the mitochondrial matrix into the intermembrane space, creating a high concentration of H⁺ outside the inner membrane and a low concentration inside. The resulting electrochemical gradient, also known as the proton motive force, drives H⁺ ions back into the matrix through ATP synthase. This movement powers the phosphorylation of ADP to ATP, providing the cell with essential energy for various functions.

How does oxidative phosphorylation relate to chemiosmosis?

Oxidative phosphorylation is closely related to chemiosmosis as it encompasses the entire process of ATP production in the mitochondria. It involves two main stages: the electron transport chain (ETC) and chemiosmosis. The ETC creates a hydrogen ion (H⁺) concentration gradient by transferring electrons through a series of redox reactions and pumping H⁺ ions into the intermembrane space. Chemiosmosis then utilizes this gradient, allowing H⁺ ions to flow back into the mitochondrial matrix through ATP synthase. This flow of ions powers the phosphorylation of adenosine diphosphate (ADP) into adenosine triphosphate (ATP), thus completing oxidative phosphorylation and generating the majority of ATP in aerobic cellular respiration.