As protons move through ATP synthase, ADP is converted into ATP through the addition of an inorganic phosphate (Pi).Hydrogen ions in the matrix space can only pass through the inner mitochondrial membrane through a membrane protein called ATP synthase.During chemiosmosis, the free energy from the series of reactions that make up the electron transport chain is used to pump hydrogen ions across the membrane, establishing an electrochemical gradient.Practice Exam 1 B/B Section Passage 2 Question 10 Take a closer look at the simplified organization and function of the ATP synthase in the figure below. As ATP synthase turns, it catalyzes the addition of a phosphate to ADP and the formation of ATP. Instead of being turned by water, it’s turned by the flow of hydrogen ions moving down their electrochemical gradient. Conceptually, ATP synthase is similar to a turbine in a hydroelectric power plant. In the inner mitochondrial membrane, ions have just one channel available: a membrane-spanning protein known as ATP synthase. Instead, hydrogen ions can move down their concentration gradient only with the help of channel proteins that form hydrophilic tunnels across the membrane. However, like many other ions, protons can’t pass directly through the phospholipid bilayer of the membrane because its core is too hydrophobic. If the membrane were open to diffusion by the ions, the ions would tend to spontaneously diffuse back across into the matrix, driven by their electrochemical gradient. The gradient is sometimes called the proton-motive force, and you can think of it as a form of stored energy, kind of like a battery. This pumping forms concentration and electrical gradients (thus, an electrochemical gradient) across the inner mitochondrial membrane. As electrons move energetically downhill through electron transport chain complexes, the complexes use the released energy to pump hydrogen ions (H+, protons) from the matrix to the intermembrane space. These electron carriers deposit their electrons into the electron transport chain. glucose) in metabolic pathways such as glycolysis and citric acid cycle are stored in NADH and FADH2. Let’s remember that highly energetic electrons extracted from food molecules (e.g.
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