Oxidative Phosphorylation Making Cellular Energy Joanne Oellers March 9, 2012

Cells Make ATP by Two Fundamentally Different Mechanisms 1. Substrate-level phosphorylation in which a phosphate group is transferred directly to ADP as occurs in glycolysis and Krebs cycle 2. Oxidative phosphorylation in which ATP is synthesized using energy from a proton gradient with the help of the enzyme ATP synthase Organisms that metabolize food with the help of oxygen perform oxidative phosphorylation to produce ATP

Oxidative Phosphorylation Is the final step in the complete breakdown of glucose through aerobic respiration Is the process by which the majority of ATP is synthesized in organisms utilizing oxygen Operates through a mechanism proposed in 1961 by Peter D. Mitchell, the Chemiosmotic Theory of Energy Transfer Chemiosmotic Theory of Energy Transfer

Chemiosmosis Includes Two Steps 1. The flow of electrons through the protein complexes called electron-transfer chains driving protons across membranes in one direction 2. An electrochemical gradient derived from those same protons moving through the enzyme ATP synthase in the opposite direction

Location of a Mitochondrion MitPred. Accessed 3/2/12http://

Oxidative Phosphorylation: Employs the products of glycolysis, the preparatory reaction, and the Krebs cycle of aerobic respiration Brings oxygen into the equation Operates using concepts you already know

Oxidative Phosphorylation Diffusion happens A protein changes shape when it combines with another substance Oxygen is an electron hog

The Electron Transport Chain Embedded in the mitochondrial membrane cristae Consists of a series of proteins that accept and pass along electrons delivered by NADH and FADH 2 After passing through the chain, electrons ultimately connect with oxygen (the electron hog)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+ e–e– Electron transport chain Matrix NADH FADH 2 NAD + ATP synthesis ATP synthase complex Cytochrome c NADH dehydrogenase FAD Intermembrane space U bc1 cytochrome oxidase

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+ e–e– O2O2 2 1 – 2 Electron transport chain Matrix FADH 2 NAD + H2OH2O ATP synthesis ATP synthase complex Cytochrome c NADH dehydrogenase FAD Intermembrane space H+H+ H+H+ H+H+ NADH U

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+ e–e– O2O2 2 1 – 2 Electron transport chain Matrix FADH 2 NAD + H2OH2O ATP synthesis ATP synthase complex mobile carrier electron transport carriers in a molecular complex FAD Intermembrane space H+H+ H+H+ H+H+ NADH

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+ H+H+ e–e– O2O2 2 1 – 2 Electron transport chain Matrix FADH 2 NAD + H2OH2O ATP synthesis ATP synthase complex Cytochrome c NADH dehydrogenase FAD Intermembrane space NADH bc1 U

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+ H+H+ e–e– O2O2 2 1 – 2 Electron transport chain Matrix FADH 2 NAD + H2OH2O ATP synthesis ATP synthase complex ADP + P Cytochrome c NADH dehyrdrogenase FAD Intermembrane space NADH bc1 U

ATP Synthase is a Molecular Turbine Thomas Meier F0F0 F1F1

Theoretical ATP Yield for Eukaryotes The chemiosmotic model suggests that one ATP molecule is generated for each proton pump activated by the electron transport chain. We would expect each molecule of NADH and FADH2 to generate three and two ATP molecules respectively.

Actual Yield is Different 1. The inner mitochondrial membrane is somewhat leaky to protons, allowing some of them to reenter the matrix without passing through ATP synthase. 2. The mitochondria may employ the proton gradient generated by chemiosmosis for purposes other than ATP synthesis, such as transporting pyruvate into the matrix.

All Types of Cells Perform Phosphorylation Eukaryotic cells o Heterotrophic o Autotrophic Prokaryotic cells Photophosphorylation

Biology, Raven et al. 9 th edition. McGraw-Hill. Photophosphorylation in a Non-sulfur Bacterium

Why Should We Try to Understand This Process? The generation of a proton gradient across a membrane and chemiosmosis leading to oxidative phosphorylation is a fundamental way for cells to make a living The operation of cells is awesome and an example of the wonder of biology

References Biology. Raven P.H., et al. 9 th ed. McGraw-Hill Biology Junction. Accessed 3/4/12. Jung’s Biology Blog. Accessed 3/4/12. Hyperbaric Oxygen Info. Accessed 3/1/12. Accessed 3/1/12 Nobel Prize.org. Accessed 3/7/12. Photobucket. Accessed 3/6/12. Reference.com. Accessed 3/4/12. The Full Wiki. Accessed 3/5/12.