Cellular Respiration Part IV: Oxidative Phosphorylation

Curriculum Framework 2A2 Organisms capture and store free energy for use in biological processes. g. The electron transport chain captures free energy from electrons in a series of coupled reactions that establish an electrochemical gradient across membranes.

Electrons carried via NADH Electrons carried via NADH and FADH2 Figure 9.6-3 Electrons carried via NADH Electrons carried via NADH and FADH2 Oxidative phosphorylation: electron transport and chemiosmosis Glycolysis Citric acid cycle Pyruvate oxidation Glucose Pyruvate Acetyl CoA CYTOSOL MITOCHONDRION Figure 9.6 An overview of cellular respiration. ATP ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation

Oxidative Phosphorylation: Electron Transport and Chemiosmosis Curriculum Framework 2A2g2. In cellular respiration, electrons delivered by NADH and FADH2 are passed to a series of electron acceptors as they move toward the terminal electron acceptor, oxygen. Oxidative Phosphorylation: Electron Transport and Chemiosmosis

Curriculum Framework t and Chemiosmosis 2A2g3. The passage of electrons is accompanied by the formation of a proton gradient across the inner mitochondrial membrane or the thylakoid membrane of chloroplasts, with the membrane separating a region of high proton concentration from a region of low proton concentration. In prokaryotes, the passage of electrons is accompanied by the outward movement of protons across the plasma membrane. t and Chemiosmosis

Electron transport chain Outer mitochondrial membrane Inner mitochondrial membrane ELECTRON TRANSPORT Electron carriers such as NADH deliver their electrons to an electron transport chain embedded in the inner membrane of the mitochondrion. The chain consists of a series of electron carriers, most of which are proteins that exist in large complexes. Electrons are transferred from one electron carrier to the next in the electron transport chain. Electron carrier (NADH) Electrons

Oxygen Electrons Hydrogen ions Let’s take a closer look at the path electrons take through the chain. As electrons move along each step of the chain, they give up a bit of energy. The oxygen you breathe pulls electrons from the transport chain … Hydrogen ions

… and water is formed as a by-product.

Hydrogen ions ATP ATP synthase Area of high hydrogen ion concentration Inner mitochondrial membrane The energy released by electrons is used to pump hydrogen ions (the blue balls) across the inner membrane of the mitochondrion, creating an area of high hydrogen ion concentration. Hydrogen ions flow back across the membrane through a turbine. Much like water through a dam, the flow of hydrogen ions spins the turbine, which activates the production of ATP. These spinning turbines in your cells produce most of the ATP that is generated from the food you eat. ATP ATP synthase

Outer mitochondrial membrane Inner mitochondrial membrane The process you’ve just observed, cellular respiration, generates 10 million ATPs per second in just one cell.

Chemiosmosis: The Energy-Coupling Mechanism Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space H+ then moves back across the membrane, passing through the enzyme, ATP synthase ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work

INTERMEMBRANE SPACE H Stator Rotor Internal rod Catalytic knob ADP + Figure 9.14 INTERMEMBRANE SPACE H Stator Rotor Internal rod Figure 9.14 ATP synthase, a molecular mill. Catalytic knob ADP + P i ATP MITOCHONDRIAL MATRIX

Protein complex of electron carriers Figure 9.15 H H H Protein complex of electron carriers H Cyt c IV Q III I ATP synth- ase II 2 H + 1/2O2 H2O FADH2 FAD Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis. NAD NADH ADP  P i ATP (carrying electrons from food) H 1 Electron transport chain 2 Chemiosmosis Oxidative phosphorylation

The energy stored in a H+ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis The H+ gradient is responsible for establishing a proton-motive force, emphasizing its capacity to do work Students are familiar with gravitational potential energy. Raise a heavy AP Biology textbook higher off the ground and you’ve increased it’s potential energy. The unfortunate part is that earlier grades have done such a good job of reinforcing GRAVIATIONAL potential energy, that students resist embracing “a separation of charge” as an electrical potential energy. We struggle with this in both this unit (separation of protons or H+ across a membrane) as well as within the nervous system. Reinforce that “potential” energy can also be a separation of CHARGED objects, molecules or subatomic particles such as protons or electrons.

Mitochondrial Membrane Name and describe three structural features that make the mitochondrial membrane effective at the process of energy transfer. Ask students to prepare a written response to this prompt.

ATP Production by Cellular Respiration Arrange these in order of energy transfer through chemiosmosis: electron transport chain Glucose proton-motive force NADH ATP

Oxidative phosphorylation: electron transport and chemiosmosis Figure 9.16 Electron shuttles span membrane MITOCHONDRION 2 NADH or 2 FADH2 2 NADH 2 NADH 6 NADH 2 FADH2 Oxidative phosphorylation: electron transport and chemiosmosis Glycolysis Pyruvate oxidation Citric acid cycle Glucose 2 Pyruvate 2 Acetyl CoA Figure 9.16 ATP yield per molecule of glucose at each stage of cellular respiration.  2 ATP  2 ATP  about 26 or 28 ATP About 30 or 32 ATP Maximum per glucose: CYTOSOL