Cellular Respiration Chapter 5 PDF

Chapter 5 Cellular Respiration Energy Flow But why?? ATP WORK LIVE Energy Flow The Sun – Ultimate source of ______ Photosynthesis – Captures energy of light – Converts it to chemical energy --> complex organic molecules WHY?...

Chapter 5 Cellular Respiration Energy Flow But why?? ATP WORK LIVE Energy Flow The Sun – Ultimate source of ______ Photosynthesis – Captures energy of light – Converts it to chemical energy --> complex organic molecules WHY????  Energy Flow Unstable Transfer Transfer of of Energy Energy Stable What do gasoline and glucose have in common? Abundance of carbon-hydrogen bonds  Good source of ______ WHY???  Energy Levels of Electrons of an Atom What kind of bond is a C-H bond?  Electrons are equidistant from nuclei. + When electrons move towards atomic nucleus, energy is ________  C-H bonds Electronegativities How do we get the energy that is stored in organic molecules? Oxidize it --> remove electrons Donor is oxidized - lose electrons Acceptor is reduced - gains electrons Reduction-oxidation reactions (REDOX) – Transfer electrons from donor to acceptor atoms  What is going to be able to remove the electrons (oxidization)? Oxidizing Agent Higher Electronegativity  Redox Reactions Equal Sharing Unequal Sharing High Energy Low Energy Unstable Stable Why?  Cellular Respiration Organisms obtain energy by oxidizing organic molecules produced by photosynthesis in a series of reactions Energy released in oxidations is captured in ATP___ Done in series of rxn’s C6H12O6 + 6 O2 + 32 ADP + 32 Pi→ 6 H2O + 6 CO2 + 32 ATP Cellular Respiration is Controlled Combustion YES EFFICIENT ! !!! NOT Same G EFFICIENT ! Different EA !!! Energy Transfer Electrons lose energy as they pass from donor to acceptor molecule Released energy is free energy that can do work In cellular respiration – End result is synthesis of _ATP____  What will carry the energy through this process? Electron Carriers  NAD+ Dehydrogenase Fig. 6-6, p. 118 Cellular Respiration: 3 Stages 1. Glycolysis 2. Citric acid cycle 3. Electron transport and chemiosmosis 1. Glycolysis Glucose is converted: – to 2 molecules of pyruvate by oxidizing and removing electrons – From NAD+ to NADH – Through series of enzyme-catalyzed reactions – ATP and NADH is synthesized 2. Citric Acid Cycle Oxidize pyruvate  Acetyl coenzyme A (acetyl-CoA) – Enters metabolic cycle – Oxidized completely to carbon dioxide – Synthesis of ATP, NADH and FADH2 3. Electron Transport and Chemiosmosis NADH synthesized by glycolysis and citric acid cycle is oxidized (also FADH2) – Liberated electrons pass along electron transport chain – Electrons transferred to O2 --> water – Free energy establishes proton gradient across membrane – Drives synthesis of _ATP____  Mitochondria Location for most cellular respiration But prokaryotes don’t have mitochondria !!! 1. Glycolysis 10 steps in the cytosol Glucose (6 carbons) is oxidized into two molecules of pyruvate (3 carbons each) Electrons removed are delivered to NAD+ producing NADH Each glucose molecule oxidized produces – 2 ATP – 2 NADH – 2 pyruvate Energy Inputs and Outputs in Glycolysis  Glycolysis – Steps 1-3 Energy Input - Consume 2 ATPs  Phosphorylation Phosphofructokinase – regulated enzyme Glycolysis – Steps 4-5 Energy Input Splitting - 1 sugar  2 G3P Glycolysis – Steps 6-7 Energy Output Production of 2 ATP by substrate-level phosphorylation Synthesis of 2 NADH by redox reaction Glycolysis – Steps 8-10 Energy Output Production of 2 ATP by substrate-level phosphorylation 2 pyruvates – less potential energy than glucose ATP ATP molecules – Produced in glycolysis – Result from substrate-level phosphorylation Substrate-level phosphorylation – Enzyme-catalyzed reaction – Transfers phosphate group from substrate to ADP ATP Synthesis by Substrate- Level Phosphorylation Same in Citric Acid Cycle Different in Oxidative Phosphorylation and Chemiosmosis ___ ATP Synthase  Pyruvate Oxidation DEHYDROGENATION DECARBOXYLATION High Energy Intermediate Pyruvate Oxidation Takes place in mitochondrial matrix Pyruvate oxidized to acetyl groups (2C) Electrons removed are accepted by NAD+ CO2 is produced Pyruvate Oxidation (cont’d) Each pyruvate molecule produces – 1 acetyl group – 1 NADH – 1 CO 2 Acetyl groups attached to coenzyme A –  Acetyl-CoA – Delivered to citric acid cycle Summary: Pyruvate Oxidation pyruvate + CoA + NAD+ acetyl-CoA + NADH + H+ + CO2 Based on 1 pyruvate but need to double if based on 1 glucose Pyruvate Oxidation and Citric Acid Cycle Pyruvate Oxidation Citric Acid Cycle 2. Citric Acid Cycle 8 enzymatic reactions Acetyl groups completely oxidized to CO2 Electrons removed in oxidations – Accepted by NAD+ or FAD Citric Acid Cycle (cont’d) Substrate-level phosphorylation – Produces _ATP___ Each acetyl group oxidized produces – 2 CO 2 – 1 ATP – 3 NADH – 1 FADH2 Summary: Citric Acid Cycle 1 acetyl-CoA + 3 NAD+ + 1 FAD + 1 ADP + 1 Pi + 2 H2O 2 CO2 + 3 NADH + 1 FADH2 + 1 ATP + 3 H+ + 1 CoA Based on 1 pyruvate but need to double if based on 1 glucose Citric Acid Cycle High Energy Redox Rxn Isomerization Hydration H2O High CO2 loss Energy Redox Rxn Redox Rxn CO2 loss ATP Synthesis Redox Rxn Electron Transfer and Chemiosmosis Respiratory Electron Transport Chain Inner mitochondrial membrane In eukaryotes Includes – 4 major protein complexes (I, II, III and IV) – 2 smaller shuttle carriers Respiratory Electron Transport Chain (cont’d) Electrons passed from NADH and FADH2 to O2 through carriers in a stepwise manner Oxygen is the final electron acceptor Electrons are depleted of energy Some energy used by complexes I and IV – To pump protons (H+) across inner mitochondrial membrane – Electrochemical gradient Electron Transfer System and Oxidative Phosphorylation Electrochemical gradient Proton- motive force  Redox Components of Electron Transport Chain Prosthetic High energy state Groups transfer electrons _No___ ATP Low energy state Production Oxidative Phosphorylation and Chemiosmosis ATP synthase catalyzes ATP synthesis using energy from the H+ gradient across the membrane (chemiosmosis) ATP synthase – Embedded in inner mitochondrial membrane with electron transfer system ATP Synthase – A Molecular Motor Driven by proton- motive force Uncoupling of Electron Transport and ATP Synthesis Efficiency of Cellular Respiration More than 30% efficiency for utilization of energy released by glucose oxidation if the H+ gradient is used only for ATP____ production ATP Production Approximate 1 NADH  2.5 ATP 1 FADH2  1.5 ATP Optimal Amount  Energy Calculation ATP  ADP + Pi = 7.3 kcal/mol 32 ATP = 32 x 7.3 kcal/mol = 233.6 kcal/mol 1 glucose = 686 kcal/mol % efficiency = 233.6 kcal/mol = ___ % 686 kcal/mol What happened to the other ~ 66 %? Oxidation of Carbohydrates, Fats, and Proteins Control of Cellular Respiration Allosteric Activator Feedback Inhibition Oxygen and Cellular Respiration Fermentation Reaction pathways In the cytosol – NADH delivers electrons – From glycolysis to organic acceptor molecules – Converting NADH back to NAD+ – Pyruvate is reduced Fermentation (cont’d) NAD+ free to accept more electrons – Removed from sugars in glycolysis ATP production by glycolysis – Continues in absence of oxygen Fermentation Fermentation Anaerobic Respiration Prokaryotes - respiratory electron transport chains on internal membrane systems Possess anaerobic respiration Sulphate, nitrate, and ferric ion are common electron acceptors Still make ATP?? Lifestyles Dictated by Oxygen Strict anaerobes: Cannot grow in presence of oxygen Strict aerobes: can not survive without oxygen Require oxygen Facultative anaerobes: Can grow in presence of oxygen and can grow using fermentative pathways Paradox of Aerobic Life Although many organisms cannot exist without oxygen because it is required for electron transport, oxygen itself is inherently dangerous to all forms of life  Reduction of Oxygen to Water Reactive Oxygen Species Defence Against Reactive Oxygen Species Reactive oxygen species (ROS) – Include superoxide, hydrogen peroxide and hydroxyl radical – Strong oxidizing agents – Lead to Alzheimers, cancer, heart disease Antioxidant defence system – Enzymes – Superoxide dismutase and catalase – Nonenzymes – Antioxidants: Vitamin C and vitamin E Putting it into Perspective 1. Why do we eat? 2. What are three stages of energy transfer? 3. How do we store the energy? Through glycolysis 4. How efficient is the process? 30-35% efficient 5. What’s the alternative pathway when no