Similarly, hydrogen ions in the matrix space can only pass through the inner mitochondrial membrane through a membrane protein called ATP synthase.
This protein acts as a tiny generator turned by the force of the hydrogen ions diffusing through it, down their electrochemical gradient. The turning of this molecular machine harnesses the potential energy stored in the hydrogen ion gradient to add a phosphate to ADP, forming ATP. Chemiosmosis is used to generate 90 percent of the ATP made during aerobic glucose catabolism. The production of ATP using the process of chemiosmosis in mitochondria is called oxidative phosphorylation.
It is also the method used in the light reactions of photosynthesis to harness the energy of sunlight in the process of photophosphorylation. The overall result of these reactions is the production of ATP from the energy of the electrons removed from hydrogen atoms. This provided the basis as to how oxidative phosphorylation led to ATP synthesis. 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.
To further explain the process of chemiosmosis and describe how it is a part of cellular respiration, see the diagram below. The figure above is a schematic diagram of the mitochondrion. It is regarded as the powerhouse of the cell because most ATPs are produced here.
It is specialized for ATP synthesis. Take note that the organelle is a double-membraned structure. The mitochondrial membrane is made up of an outer membrane and an inner membrane. Both layers consist of lipid layers that prohibit the easy passage of ions. In between the two membranes is the intermembrane space. The inner membrane forms many infoldings called cristae. The space within the inner membrane is called the mitochondrial matrix.
The matrix is the location of the citric acid cycle, a cyclic metabolic reaction where food molecules are churned to generate energy-rich phosphate compounds.
The pyruvate from glycolysis is converted into acetyl CoA that will enter the mitochondrion for complete oxidation and degradation into carbon dioxide. For every pyruvate molecule, the citric acid cycle will generate one ATP via substrate phosphorylation. Most of the ATP will come from oxidative phosphorylation, which will take place at the mitochondrial membrane where the electron transport chain ETC and the enzyme ATP synthase are embedded.
These electron-carrying molecules will shuttle the electrons to the ETC for oxidative phosphorylation. As the electrons are passed along the chain, every ETC member undergoes a redox reaction, accepting and donating electrons. The passing of electrons will reach the end — when the electrons are passed on to the final electron acceptor, the molecular oxygen. See the diagram above As protons are pumped across, protons thereby accumulate on one side of the membrane.
Researchers referred to it specifically as the proton-motive force. They define the term as the energy generated by the transfer of protons or electrons across an energy-transducing membrane.
The protons will move down to their gradient, i. The energy causes the rotor and the rod of the enzyme to rotate. Chemiosmosis is about energy coupling.
The relationship between chemiosmosis and ATP synthesis lies in the generation of a proton motive force. As explained earlier, cellular respiration employs chemiosmosis as the mechanism that drives ATP synthesis by oxidative phosphorylation. The electrons from the citric acid cycle where pyruvate-turned-acetyl coenzyme A is broken down to carbon dioxide are transferred to electron carriers to shuttle them to the ETC.
The proton motive force that will develop from the protons accumulating on one side of the membrane during the energy transfer via a series of redox reactions in the ETC will, in turn, be used to build ATP from ADP and inorganic phosphate. As a result, there will be fewer ATP end products without chemiosmosis to incur the process.
The same impact can be expected in photosynthesis where chemiosmosis is also a crucial step in ATP production. As described above, chemiosmosis takes place in the mitochondria of eukaryotes. But aside from the mitochondria, photosynthetic eukaryotes, such as plants, have another organelle where chemiosmosis takes place — the chloroplast.
The chloroplast is the organelle involved primarily in photosynthesis. It has a thylakoid system that harvests light. Thus, it serves as the location for the light reactions or light-dependent processes. The matrix of the chloroplast is referred to as the stroma. It is the thick fluid that contains enzymes, molecules, and other substrates involved in the dark reactions or light-independent processes.
In chloroplast, chemiosmosis occurs in the thylakoid. This membrane system has its own transport chain and ATP synthases. One of the major differences between chemiosmosis in mitochondria and in chloroplasts is the source of energy.
In mitochondria, the high-energy electrons are extracted from the food molecule from redox reaction whereas in chloroplast the source is from the photons captured from the light source. In prokaryotes such as bacteria and archaea, chemiosmosis occurs in the cell membrane since these organisms lack mitochondria and chloroplasts.
The hydrogen ions protons move across the biological membrane via the ATP synthase a transport protein when a proton gradient forms on the other side of the membrane. The proton gradient forms when the hydrogen ions accumulate as they are forcibly moved to the other side during the electron transport and redox reactions. As more hydrogen ions are on the other side they will move back to the cell move by crossing the membrane through the ATP synthase.
Oxidative phosphorylation is a metabolic pathway that generates ATP from the energy produced through a series of redox reactions in the ETC. Thus, it is also called electron transport-linked phosphorylation.
It is an aerobic process since molecular oxygen is the final electron acceptor.
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