What Is Chemiosmosis?: Structure, Functions & Types (2023)

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Chemiosmosis is the movement of ions down an electrochemical gradient through a semipermeable membrane. For instance, hydrogen ions (H+) move across a membrane during photosynthesis or in cellular respiration to form adenosine triphosphate (ATP). In a channel (red), the ions can pass through an ion gradient that has potential energy. In order to make ATP, a concentration gradient of hydrogen ions, or protons, across a membrane is exploited, which diffuses from areas of high proton concentration to areas of lower proton concentration. Because it involves the diffusion of water across a membrane, chemiosmosis is related to osmosis.

Chemiosmosis is the process by which ATP is made. By allowing protons to pass through the membrane, ATP is made by phosphorylating adenosine diphosphate (ADP). By using chemiosmosis to produce ATP, mitochondria, and chloroplasts, as well as bacteria and archaea, produce hydrogen ions (protons) via thylakoid membranes to the stroma (fluid). By reducing the free energy difference between the electron and proton, ATP synthase can allow proton to pass through them and in turn, make ATP by photophosphorylation of ADP.

What is Chemiosmosis?

An electrochemical gradient can be used to drive ATP synthesis in living cells when chemiosmosis occurs. Chemiosmosis refers to the process of moving ions (e.g. protons) across membranes. With the help of the proteins embedded in the membrane, the gradient also causes the ions to passively return to the plasma. In passive motion, the ions move from areas with higher concentrations of the atoms to areas with lower concentrations.

Water molecules passively move in this process, similar to osmosis. Chemiosmosis, however, involves the movement of ions across the membrane, whereas osmosis involves the movement of water molecules. In either case, a gradient is necessary. This is known as an osmotic gradient in osmosis.

In osmosis, pressure differences between opposing membrane sides produce the reaction. A proton gradient is an electrochemical gradient that drives chemiosmosis. Osmosis and chemiosmosis are not the only similarities. As well as paralleling passive transport, facilitated diffusion is another similar method. The principle is the same.

It is downhill for the ions. Membrane proteins are also responsible for carrying molecules across the membrane. Basically, the bilipid structure of the membrane prevents ions from permeating it readily, so membrane proteins allow them to move across. Various membrane proteins serve as temporary shuttles, channels, or passageways for the movement of these particles. A membrane protein transports an ion during chemiosmosis.

Additionally, these mechanisms require no chemical energy (e.g. ATP), unlike active transport. A gradient of ions forms in chemiosmosis, which generates potential energy sufficient to drive the process. Chemiosmosis occurs where? During the respiration process as well as in chloroplasts, it occurs in eukaryotes during photosynthesis. Prokaryotes lack these organelles and therefore chemiosmosis will occur in their cell membrane.

Chemiosmosis Model

The process of chemiosmosis allows living things to produce energy by coupling energy with ATP. As part of cellular respiration, it is one of the major processes. The diagram below illustrates how chemiosmosis contributes to cellular respiration and further explains how it occurs.

An illustration of the mitochondrion is shown above. Because most ATPs are produced in this area, it is known as the cellular powerhouse. ATP synthesis is its primary function. There are two membranes on the organelle. Membranes on both sides of the mitochondrial ring make up the mitochondrial membrane. Both layers consist of lipid layers, which preventions from passing easily. The intermembrane space is situated between two membranes.

There are many infoldings in the membrane. In the inner membrane of the mitochondria, there is a space called the mitochondrial matrix. The matrix is home to the citric acid cycle, a cyclic metabolic reaction where food molecules churn to generate phosphate compounds with high energy. The pyruvate that is generated during glycolysis is converted to acetyl CoA, which is then oxidized and broken down into carbon dioxide in the mitochondrion.

Through substrate phosphorylation, the citric acid cycle produces one ATP for every pyruvate molecule. The electron transport chain (ETC) and ATP synthase are embedded in the mitochondrial membrane where most of the ATP comes from oxidative phosphorylation.

Most of the high-energy electrons are transferred to NAD+ and FAD to produce NADH (and H+) and FADH2, respectively, through redox reactions. By transporting electrons to the ETC for oxidative phosphorylation, these molecules shuttle electrons to the ETC.

Each member of the ETC undergoes a redox reaction as electrons are passed along the chain. As electrons are passed from one electron acceptor to another, the molecular oxygen will receive all the electrons. Water is formed as a result of the reaction:

2 H+ + ½ O2 → H2O

ATP is not produced by ETC. Instead, H+ (protons) are pumped into the intermembrane space as electrons are passed along. (See the diagram above) While protons are being pumped across the membrane, they accumulate on one side. Gradients of proton-ion (H+) are created in this way. Proton-motive force is the name given to it by scientists. A proton (or electron) can be converted to energy by transferring it across a membrane transmitting energy.

Bypassing through the ATP synthase channel, protons will move into their gradient, which is between the intermembrane space and the matrix. ATP is synthesized by the movement of hydrogen ions across the ATP synthase, which releases the energy. The energy causes the rotor and the rod of the enzyme to rotate. The enzyme is, then, activated to harness this force so as to build the high-energy bond between the ADP molecule and the inorganic phosphate (Pi) to produce an ATP molecule. The reaction: ADP + Pi → ATP.

Function of Chemiosmosis

The process of chemiosmosis involves energy coupling. It is believed that chemiosmosis promotes ATP synthesis by generating a proton motive force. By oxidative phosphorylation, chemiosmosis drives cellular respiration by driving ATP synthesis. To shuttle electrons to the ETC, electrons from the citric acid cycle (where pyruvate-turned-acetyl coenzyme A is broken down to carbon dioxide) are transferred to electron carriers.

By building ATP from ADP and inorganic phosphate, the proton motive force that develops from the accumulation of protons on one side of the membrane will be used to transfer energy. Therefore, the ATP synthase cannot be driven by proton motion without chemiosmosis. As a result, fewer ATP end products will result without the need for chemiosmosis. A similar impact can be expected in photosynthesis, where chemiosmosis plays a crucial role in ATP synthesis.

Chemiosmosis Examples

  1. Chemiosmosis in chloroplasts

The process of chemiosmosis takes place in the mitochondria of eukaryotes. Photosynthesis occurs in eukaryotes, including plants, in addition to the mitochondria – the chloroplast.

Chloroplasts are organelles primarily responsible for photosynthesis. It harvests light through its thylakoid system. As such, it governs the reactions initiated by light (or processes triggered by light). The chloroplast matrix is known as the stroma. The dark reactions (or light-independent processes) are carried out in the thick liquid that contains enzymes, molecules, and other substrates.

Thylakoids in chloroplasts undergo chemiosmosis. ATP synthases and a transport chain are part of this membrane system. In chloroplasts chemiosmosis is energy-dependent; in mitochondria, it is not. Unlike mitochondria, chloroplasts capture photons directly from the light source, rather than obtaining electrons from food molecules (derived from redox reactions).

H+ ions accumulate in the thylakoid compartment (i.e., the space inside the thylakoid) to form the proton gradient (H+). A stromal H+ ion can be formed by (1) splitting water during the light reactions; (2) translocating protons via the transport chain; or (3) picking up H+ ions by NADP+ during the light reactions. ATP synthases embedded in the thylakoid membrane let the H+ ions across the membrane and diffuse to the stroma as they are greater in number inside this compartment (lumen).

  1. Chemiosmosis in prokaryotic cells

Chemiosmosis occurs in the cell membrane of prokaryotes like bacteria and archaea, which lack mitochondria and chloroplasts.

Diagram of chemistryosmosis in photosynthetic bacterium’s cell membrane. In the case of a proton gradient forming on the other side of the membrane, hydrogen ions (protons) are transported across the biological membrane by ATP synthase (a transport protein).

In electron transport and redox reactions, the hydrogen ions are forced to accumulate on the other side in order to form a proton gradient. ATP synthase allows the hydrogen ions to cross the membrane to get back into the cell as they move further away from it on the side where more hydrogen ions are. Through phosphorylation, energy is released to convert ADP to ATP.

Chemiosmosis vs Oxidative Phosphorylation

ATP is produced in the ETC by oxidative phosphorylation, a metabolic pathway that uses energy generated by redox reactions. In addition to electron transport-linked phosphorylation, this is also called phospholipid phosphatase. Due to the final electron acceptor being molecular oxygen, this is an aerobic process. This distinguishes it from the other form of phosphorylation, namely the substrate-level phosphorylation, where ATP is generated directly from an intermediate substrate. In contrast, oxidative phosphorylation is an indirect method of synthesizing ATP. Protons are moved across the membrane with the help of chemiosmosis.

Oxidative phosphorylation directly makes ATP through chemiosmosis. The ATP synthase, however, will not be able to do so without the proton motive force that results from the electron transfer chain that moves protons (H+) to the other side of the membrane as the electrons are passed along.

Important Points to Remember

  • Chemical reactions in the electron transport chain generate free energy that is used to pump hydrogen ions across the membrane during chemiosmosis, establishing an electrochemical gradient.
  • The inner mitochondrial membrane only allows ions of hydrogen to pass through it thanks to a membrane protein called ATP synthase.
  • ADP is turned into ATP by the ATP synthase while protons move through it.
  • In mitochondria, oxidative phosphorylation uses chemiosmosis to produce ATP.

Important Terms to Remember

  1. ATP synthase: An important enzyme that provides energy for the cell to use through the synthesis of adenosine triphosphate (ATP).
  2. Oxidative phosphorylation: A metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate (ATP).
  3. Chemiosmosis: The movement of ions across a selectively permeable membrane, down their electrochemical gradient.

Frequently Asked Questions About Chemiosmosis

How Does Chemiosmosis Produce ATP?

ATP Synthase Harnesses The Potential Energy Stored In The Hydrogen Ion Gradient To Add A Phosphate To ADP, Forming ATP, Using The Hydrogen Ion Gradient Form by the Electron Transport Chain.

What Is The Role Of Chemiosmosis?

Chemiosmosis Is One Of The Major Steps In Cellular Respiration. It Is One Of A Set Of Energy-coupling Mechanisms Used By Living Organisms.

What Is An Example Of Chemiosmosis?

An Example Of Chemiosmosis In The Cell Is The Hydrogen Ion Gradient Used By ATP Synthase To Create Cellular Energy Or ATP. Hydrogen Ions Flow From Outside The Cell To Inside, And The Energy Released Is Harnessed By ATP Synthase To Make ATP.

What Are The Products Of Chemiosmosis?

As Ions Pass-Through Semipermeable Membrane-Bounded Structures, they progress along their electrochemical gradient. In Cellular Respiration Or Photosynthesis, Hydrogen Ions (H+) Travel Across A Membrane To Produce Adenosine Triphosphate (ATP).

Does Chemiosmosis Require Oxygen?

Chemiosmosis Is Used To Produce ATP By Oxidative Phosphorylation In The Electron Transport Chain. Oxygen Acts As A Final Electron Acceptor In The Electron Transport Chain, So In The Absence Of Oxygen The Ets Will Stop Working And There Will Be No ATP Production By Chemiosmosis.

What Is Not Required For Chemiosmosis?

Closed Membrane System Is Not Required. Only A Membrane Is Required For The Development Of A Proton Gradient Across The Membrane Of The Thyllakoid And The Proton Accumulation Is Towards The Inside Of The Membrane. So, The Correct Answer Is a ‘closed Membrane System’.


What is the function of chemiosmosis? ›

Chemiosmosis is an energy-coupling mechanism employed by living organisms to produce ATP. In respiring cells, it is one of the major steps of cellular respiration.

What is chemiosmosis short answer? ›

Chemiosmosis is the movement of ions across a semipermeable membrane bound structure, down their electrochemical gradient. An important example is the formation of adenosine triphosphate (ATP) by the movement of hydrogen ions (H+) across a membrane during cellular respiration or photosynthesis.

What is the most important structure in chemiosmosis? ›

Mitochondria are membrane-enclosed organelles regarded as 'cell power plants. ' Mitochondria generate most of the ATP in cells via ATPase rotation driven by the proton flow across the inner membrane by a process called chemiosmosis.

What is the definition of chemiosmosis in biology? ›

Chemiosmosis is the process of diffusion of ions (usually H+ ions, also known as protons) across a selectively permeable membrane. As in osmosis, chemiosmosis leads to a concentration gradient of the diffusing ion across the membrane. A concentration gradient is a form of potential energy that can do work.

What is chemiosmosis and where does it occur? ›

Cellular respiration is the mechanism through which sugar (glucose) is converted into energy within cells. Chemiosmosis occurs in the chloroplasts during photosynthesis, and in the mitochondria during respiration. Chemiosmosis is the method through which ATP is produced during cellular respiration.

What is the process of chemiosmosis quizlet? ›

What is the process of chemiosmosis? Chemiosmosis is the process by which chemical ions move from an area of high concentration to an area of low concentration across a selectively permeable membrane. Chemiosmosis is the process by which ATP, or adenosine triphosphate, is synthesized (from ADP).

What is chemiosmosis Quizizz? ›

The process of using electrons to pump H+ to create an electrochemical gradient that must flow through a protein is called: Chemiosmosis.

Why is it called chemiosmosis? ›

Peter Mitchell proposed that an electrochemical concentration gradient of protons across a membrane could be harnessed to make ATP. He likened this process to osmosis, the diffusion of water across a membrane, which is why it is called chemiosmosis.

What does chemiosmosis require? ›

-For chemiosmosis to occur a proton gradient must be present, a membrane, a proton pump, and ATP synthase enzyme that is responsible for the synthesis of ATP which has to be used in the Calvin cycle.

How many ATP are made in chemiosmosis? ›

One ATP molecule is produced per round of the Krebs cycle, and two cycles occur for every molecule of glucose, producing a net total of two ATP. Finally, 26 or 28 ATP are produced in the electron transport chain through oxidative phosphorylation, depending on whether NADH or FADH2 is used as the electron carrier.

What type of transport is chemiosmosis? ›

The chemiosmotic theory states that the transfer of electrons down an electron transport system through a series of oxidation-reduction reactions releases energy. This energy allows certain carriers in the chain to transport hydrogen ions (H+ or protons) across a membrane.

What are the main functions of the electron chain? ›

The primary function of the electron transport chain is to generate an electrochemical gradient. It drives the synthesis of ATP during cellular respiration and photosynthesis in mitochondria and chloroplasts, respectively. It is used in cellular respiration.

What are the four requirements for the chemiosmosis to occur? ›

The factors required are :
  • Electrochemical gradient.(proton gradient).
  • Membrane separating.
  • Proton pump .
  • ATP synthase for synthesising ATP.

Which of the following is the best definition of chemiosmosis? ›

Which of the following best describes the process referred to as "chemiosmosis"? A concentration gradient of protons across the inner mitochondrial membrane is utilized to produce ATP.

What happens to ATP in chemiosmosis? ›

After an ATP molecule has been used to do work (i.e. it has released its energy), it is converted into adenosine diphosphate (ADP).

Is chemiosmosis a reaction? ›

The chemiosmosis reaction takes place in the matrix of the chloroplast known as the stroma which has a high amount of protons (hydrogen ions).

What is the major feature of chemiosmosis? ›

Chemiosmosis involves the pumping of protons through special channels in the membranes of mitochondria from the inner to the outer compartment. The pumping establishes a proton (H+) gradient. After the gradient is established, protons diffuse down the gradient through a transport protein called ATP synthase.

Does chemiosmosis require oxygen? ›

Oxygen acts as the final electron acceptor in the electron transport chain. Without oxygen, the electron transport chain will stop and there will be no generation of ATP. So, oxygen is an important thing in the chemiosmosis process.

What does chemiosmosis not require? ›

So, the correct answer is 'Closed membrane system'.

What is the role of chemiosmosis quizlet? ›

Chemiosmosis generates 90 percent of the ATP made during glucose catabolism and is also the method used in the light reactions of photosynthesis to harness the energy of sunlight.

What is the role of chemiosmosis in mitochondria quizlet? ›

Chemiosmosis is the movement of ions across a semipermeable membrane. More specifically, it relates to the creation of ATP as hydrogen ions travel across the membranChemiosmosis involves the pumping of protons through specific passageways in the membranes of the mitochondria from the inner to the outer space.

What is the role of chemiosmosis in photosynthesis? ›

What is the role of chemiosmosis in photosynthesis? During light-dependent reactions of photosynthesis, chemiosmosis is the process by which light energy is converted to chemical energy in the form of ATP to be used in dark reactions.

What does chemiosmosis use to make ATP? ›

In the electron transport chain, electrons are passed from one molecule to another, and energy released in these electron transfers is used to form an electrochemical gradient. In chemiosmosis, the energy stored in the gradient is used to make ATP.

What is needed in chemiosmosis? ›

-For chemiosmosis to occur a proton gradient must be present, a membrane, a proton pump, and ATP synthase enzyme that is responsible for the synthesis of ATP which has to be used in the Calvin cycle.


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