BIO 101 1st Edition Lecture 13 Outline of Last Lecture I Enzymes a Catalysts b Free Energy of Activation II Factors Affecting Enzyme Activity III Control of Metabolism IV Feedback Inhibition V ATP and Cellular Work Outline of Current Lecture I Cellular Respiration II Redox Reactions a Oxidation b Reduction III Four Stages of Respiration a Glycolysis b Transition to Mitochondria c Krebs Cycle d Oxidative Phosphorylation Chapter 9 Cellular Respiration Cellular respiration aerobic requires O2 catabolism breakdown of organic carbon based nutrients food Nutrients have potential energy stored in chemical bonds Goal of cellular respiration is to convert to stable chemical energy in nutrients to a readily useable form ATP Strategy is to extract energy from nutrients in a stepwise manner a series of chemical reactions CATABOLIC PATHWAY Overall chemical equation for the whole pathway During this pathway the cell makes 36 ATPs glucose Each ATP made requires 7 3 kcal mole of energy Yield of respiration is therefore 263 686 38 60 of the energy of glucose is lost used to drive some endergonic reaction or lost as heat 405 is saved in form of ATP Redox Reactions The cell get energy from glucose during cellular respiration using a series of OXIDATION REDUCTION reaction Oxidation loss of electrons BIO 101 1st Edition Reduction gain of electrons Called redox because these 2 kinds of reactions are always coupled in the cell One molecule loses an electron becomes oxidized and the electron is gained by another molecule becomes oxidized and the electron is gained by another molecule becomes reduced The loss and gain of electrons can be easily thought of as loss and gain of whole H atoms because the electron is often accompanied by a proton Hatom Easy to monitor oxidation as loss of H atoms and reduction as gain of Hatoms Overview of Respiration During respiration glucose is broken down to CO2 and oxidized electrons stripped off Electrons usually H atoms are removed in a series of REDOX reactions catabolic pathway Electrons from glucose are eventually transferred to O2 which is the REDUCED to H2O Overall process is exergonic and releases energy in a stepwise manner Some of the energy is captured in the form of ATP Four Stages of Respiration 1 Glycolysis A catabolic pahway with 10 chemical reactions Occurs in all living cells ex of unity in life Although the overall respiration pathway requires O2 this first stage DOES NOT require oxygen Occurs in cytoplasm Overall pathway for glycolysis Glucose 6 carbon is split into 2 pyruvates 3 carbons Glucose is partially OXIDIZED some electrons are removed OXIDATION of glucose is catalyzed by enzymes called DEHYDROGENASES o Generally 2 H atoms are removed by dehydrogenases o Dehydrogenases require CO ENZYMES to work small organic non protein molecules o The coenzymes act as temporary carriers for the electrons that are removed during oxidation reactions o There are TWO important coenzymes that work with dehydrogenases during respiration BIO 101 1st Edition Two Coenzymes that are required for Dehydrogenases 1 Nicotinamide Adenine dinucleotide NAD vitamin B derivative exists is 2 forms 2 Flavin adenine dinucleotide FAD riboflavin derivative also exists in 2 forms these coenzymes are only ACTIVE in their OXIDIZED FORMS this is the form available to accept electrons glycolysis produces a NET GAIN of 2 ATPs per glucose molecule that enters the pathway these 2 ATPs arise by SUBSTRATE LEVEL PHOSPHORYLATION substrate level phosphorylation direct transfer of a phosphate from an intermediate substrate in the pathway to ADP making ATP glycolysis also produces 2 NADHs reduced coenzyme these will be important in the last stage of respiration in which ATP is generated by oxidative phosphorylation OVERALL FOR GLYCOLYSIS Reactant products 1 Glucose 2 pyruvates can be used later to 2 ATPs make ATP 2 NADH 2 Transition to Mitochondria glycoslysis occurs in the cytoplasm the rest of respiration occurs in the mitochondria Pyruvate from glycolysis enters the matrix of mitochnodria As it enters it is further OXIDIZED and broken down Pyruvate has 3 carbons as it enters the mitochondria one carbon is completely oxidized and pulled OFF of pyruvate producing CO2 BIO 101 1st Edition The remaining 2 carbon group called acetyl group is carried into the mitochondria by a molecule called COENZYME A CoA acetyl CoA acetyl CoA The electrons removed from pyruvate are transferred to NAD NADH the overall process is this What goes in 2 pyruvates can be used later to make ATP 3 Krebs Cycle Citric Acid Cycle Catabolic pathway Occurs in matrix of mitochondria Occurs only in presence of O2 2 carbon acetyl group is COMPLETELY broken down and OXIDIZED to give 2 CO2 electrons are transferred to NAD and FAD to produce NADH and FADH2 is called a cycle because oxaloacetate one of the beginning reactants is regenerated by the reactions What goes in Products 2 acetyl groups 4 CO2 2 ATP substrate level phos 6 NADH 2 FADH2 Oxidative Phosphorylation occurs on the inner mitochondrial membrane uses electrons that were transferred to NADH and FADH2 in stages 13 REDUCED COENZYMES 4 What are products 2 acetyl CoA 2 CO2 2 NADH BIO 101 1st Edition electrons carried by REDUCED COENZYMES are dropped at the ELECTRON TRANSPORT CHAIN ETC electron transport chain series of electron carrier molecules located on inner mitochondrial membrane electrons from the reduced coenzymes NADH and FADH2 are passed along the chain and eventually to O2 FINAL ELECTRON ACCEPTOR During some electron transfers along the electron transport chain protons H are pumped from the matrix into the inner membrane space creating a H gradient proton gradient Proton gradient potential energy PROTON MOTIVE FORCE Protons can re enter the matrix of mitochondria down their electrochemical gradient using a special transport protein called ATP synthase transport protein for protons but ALSO an ENZYME that catalyzes reaction ADP phosphate ATP As proton pass through ATP synthase energy of proton gradient is harnessed to drive the endergonic reaction CHEMIOSMOSIS using energy of proton gradient to make ATP for every NADH that drops electrons at electron transport chain enough energy is captured to make 3 ATPs NADH 3 ATPs every FADH2 can be used to make 2 ATPs FADH2 2 ATPs most of the ATP in the cell is produced by chemiosmosis 90 other important aspect is that NAD and FAD OXIDIZED forms of the coenzymes are regenerated when they drop off their electrons they are now