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Cellular Respiration Harvesting energy at the cellular level 1 2 Cellular Respiration vs. Breathing Breathing Cellular Respiration Moving air into and out of lungs…gas exchange Breaking down food (glucose) to release the potential energy. How are they related? 3 Types of Metabolism Aerobic metabolism Occurs when enough oxygen reaches cells to support energy needs. Anaerobic metabolism Occurs when the demand for oxygen is greater than the body’s ability to deliver it. 4 Main Types of Energy-Releasing Pathways Anaerobic pathways Evolved first Don’t require oxygen Start with glycolysis in cytoplasm Completed in cytoplasm Aerobic pathways Evolved later Require oxygen Start with glycolysis in cytoplasm Completed in mitochondria 5 Chemical Cycling between Photosynthesis and Cellular Respiration Recall… The ingredients for photosynthesis are carbon dioxide and water. CO2 is obtained from the air by a plant’s leaves. H2O is obtained from the damp soil by a plant’s roots. Chloroplasts rearrange the atoms of these ingredients to produce sugars (glucose) and other organic molecules. Oxygen gas is a by-product of photosynthesis. 6 Remember… 7 ATP Is Universal Energy Source Photosynthesizers get energy from the sun Animals get energy second- or third-hand from plants or other organisms Regardless, the energy is converted to the chemical bond energy of ATP 8 Cellular Respiration Equation Function: Location: Convert energy stored in glucose into ATP Cytoplasm and mitochondria Its sort of looks like the photosynthesis reaction…only in reverse. 9 Cellular Respiration Overview Glycolysis Kreb’s Cycle Electron Transport Chain 10 The Role of Coenzymes NAD+ and FAD accept electrons and hydrogen Become NADH and FADH2 (When they are reduced) Deliver electrons and hydrogen to the electron transfer chains Think of them as “delivery molecules”…carrying their cargo of electrons and hydrogen ions They pick up their cargo in one part of the cell, and deliver it to another “drop off” site in the cell. Function during REDOX reactions – reactions that involve the movement of electrons between reactants. 11 A closer look at REDOX reactions: Comprised of two subreactions Reduction – when an electron is gained Oxidation – when an electron is lost “LEO the lion says GER” Carbon atoms in food molecules will be oxidized (stripped of their electrons), producing CO2. The electrons will eventually be gained by oxygen (in a reduction step) to produce METABOLIC H2O. 12 Glucose A simple sugar (C6H12O6) Atoms held together by covalent bonds Contains Potential energy 13 Cellular Respiration Overview Glycolysis Kreb’s Cycle Electron Transport Chain 14 Glycolysis is the first part of cellular respiration. It is an ancient pathway for metabolism OCCURS WHETHER OXYGEN IS PRESENT OR ABSENT! Nearly all life, both prokaryotic and eukaryotic, do glycolysis the same way The enzymes of glycolysis are located in a cellular space common to both prokaryotes and eukaryotes….which is….? 15 Glycolysis Occurs in Two parts Energy-requiring steps ATP energy activates glucose and its six-carbon derivatives Energy-releasing steps The products of the first part are split into three-carbon pyruvate molecules ATP and NADH form 16 Energy-Requiring Steps of Glycolysis Energy-Requiring 2 ATP invested Steps glucose ATP ADP P glucose-6-phosphate P fructose-6-phosphate ATP ADP P P fructose1,6-bisphosphate P PGAL P PGAL 17 P NAD+ Pi PGAL NADH P P 1,3-bisphosphoglycerate ADP ATP P 3-phosphoglycerate P 2-phosphoglycerate H2O P Energy-Releasing Steps Step #6 is crucial For ATP production! NAD+ is required And NADH is formed PEP ADP ATP pyruvate 18 Glycolysis: Net Energy Yield Energy requiring steps: 2 ATP invested Energy releasing steps: 2 NADH formed 4 ATP formed, 2 pyruvates Net yield is 2 ATP, 2 NADH and 2 pyruvate molecules This is NOT enough ATP energy to Support higher life…the process continues 19 Mitochondrial Anatomy 20 Cellular Respiration Overview Glycolysis Kreb’s Cycle Electron Transport Chain 21 Second Stage Reactions Preparatory reactions Pyruvate is oxidized into two-carbon acetyl units and carbon dioxide NAD+ is reduced to form NADH Krebs cycle (the citric acid cycle) The acetyl units are oxidized to carbon dioxide NAD+ and FAD are reduced to form NADH and FADH2 22 Preparatory Reactions pyruvate NAD+ coenzyme A (CoA) NADH O O carbon dioxide CoA acetyl-CoA PYRUVATE must be converted into Acetyl CoA before it can enter the Krebs cycle. 23 =CoA acetyl-CoA Krebs Cycle CoA oxaloacetate citrate NADH H2O NAD+ H2O malate NAD+ H2O FADH2 isocitrate NADH fumarate O O α-ketoglutarate FAD NAD+ NADH CoA O O succinate succinyl-CoA ATP ADP + phosphate group 24 The Krebs Cycle (the citric acid cycle) Overall Reactants Acetyl-CoA 3 NAD+ FAD ADP and Pi Overall Products Coenzyme A 2 CO2 3 NADH FADH2 ATP 25 Results of the Krebs Cycle All of the carbon molecules in pyruvate end up in carbon dioxide gas. What does the cell do with the CO2 ? Coenzymes are reduced (they pick up electrons and hydrogen) One molecule of ATP is formed Four-carbon oxaloacetate is regenerated so that the “wheel” can turn once more! (assuming there is another acetyl CoA being delivered) 26 Coenzyme Reductions During First Two Stages Glycolysis Preparatory reactions Krebs cycle 2 NADH 2 FADH2 + 6 NADH Total 2 FADH2 + 10 NADH 2 NADH There is potential energy still left in these Molecules! 27 Cellular Respiration Overview Glycolysis Kreb’s Cycle Electron Transport Chain 28 Electron Transfer and Oxidative Phosphorylation Occurs in the mitochondria Coenzymes deliver electrons to electron transfer systems (electron cargo is delivered!) Oxidized coenzymes go back to glycolysis (step #6) and Krebs cycle to allow them to continue! Electron transfer through the chain sets up a H+ ion gradient Flow of H+ down gradient powers ATP formation 29 Creating an + H Gradient OUTER COMPARTMENT NADH e- ee- NAD+ (Back to Earlier Steps) ee- INNER COMPARTMENT H2O eO2 + e- e- Metabolic water (water made from metabolism) 1. As NADH is oxidized, the electrons leave NADH and enter the electron transport chain. The electrons flow towards and eventually combine with oxygen to form metabolic water 2. As the electrons flow through the chain, hydrogen ions are PUMPED across 30 the membrane! Importance of Oxygen Electron transport and oxidative phosphorylation requires the presence of oxygen Oxygen withdraws spent electrons from the electron transport system, then combines with H+ to form Metabolic water What is the difference between water you drink and metabolic water? 31 Making ATP in the mitochondria ATP INNER COMPARTMENT ATP synthase ADP + P 1. Hydrogen ion “flow” down their gradient back into the inner compartment through ATP Synthase. 2. As they flow through the enzyme, it rotates (like a generator), and combines ADP + P (a phosphate group) and forms ATP! 3. The SPEED of the flow, POWERS the “recharging” of the ATP “battery”! 32 Summary of Energy Harvest (per molecule of glucose) Glycolysis Krebs cycle and preparatory reactions 2 ATP formed by substrate-level phosphorylation Electron transport phosphorylation 2 ATP formed by substrate-level phosphorylation 28 - 30 ATP formed ADDING IT ALL TOGETHER GIVES YOU AROUND 32 ATP MOLECULES PER GLUCOSE! 33 Fermentation Pathways Begin with glycolysis Are anaerobic: don’t require oxygen Yield only the 2 ATP from glycolysis. Doesn’t use mitochondria. Occurs in the cytoplasm 2 ATP/glucose only supports “higher” life for a short time. Humans use this only transiently! Steps in fermentation serve only to regenerate NAD+ so that glycolysis can continue. 34 Lactate Fermentation HUMANS DO THIS GLYCOLYSIS C6H12O6 2 STEP #6 ATP energy input 2 NAD+ 2 ADP 2 4 NADH ATP energy output 2 pyruvate 2 ATP net LACTATE FORMATION LDH enzyme electrons, hydrogen from NADH 2 lactate 35 GLYCOLYSIS Alcoholic Fermentation C6H12O6 2 ATP energy input STEP #6 2 NAD+ 2 ADP 2 4 NADH ATP 2 pyruvate energy output 2 ATP net ETHANOL FORMATION 2 H2O 2 CO2 YEAST DO THIS ADH enzyme 2 acetaldehyde electrons, hydrogen from NADH 2 ethanol 36 Alternative Energy Sources FOOD fats fatty acids glycerol glycogen complex carbohydrates proteins simple sugars amino acids glucose-6-phosphate NH3 GLYCOLYSIS PGAL carbon backbones urea pyruvate acetyl-CoA KREBS CYCLE 37 Evolution of Metabolic Pathways When life originated, atmosphere had little oxygen Earliest organisms used anaerobic pathways Later, the evolution of photosynthesis increased atmospheric oxygen Cells arose that used oxygen as final acceptor in electron transport and energy harvesting became more efficient! 38