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Cellular Respiration Chapter 9 Overview • Sunlight is the main source of all energy for an ecosystem • Photosynthesis converts sunlight to glucose (chemical energy) in chloroplasts Light energy ECOSYSTEM Photosynthesis in chloroplasts CO2 + H2O Cellular respiration in mitochondria – Autotrophs only • Glucose is then converted to ATP by the mitochondria through cellular respiration – Autotrophs and heterotrophs ATP powers most cellular work Heat energy Organic molecules + O2 ATP • Needed by all cells to do work – energy • Must be regenerated or recycled – 2nd law thermodynamics ATP Oxidation - Reduction (Redox) Reactions • Oxidation – loss of electrons from one substance – Glucose • Reduction – addition of electrons to another substance – Oxidizing agent accepts electrons – Oxygen – as electrons are transferred to oxygen energy is released • Oxygen is very electronegative which makes it a good oxidizing agent – electron acceptor Cellular Respiration: An overview C6H12O6 + 6O2 6CO2 + 6H2O + ATP Cell Respiration Overview The Mitochondria • Site of ATP production • Double Membrane • Critsae – infoldings of the inner membrane – Increases surface area • Mitochondrial Matrix – Inside of inner membrane containing many enzymes Cell Respiration Overview • C6H12O6 + 6O2 6CO2 + 6H2O + ATP – 3 step process • 1. Glycolysis – glucose lysis – breakdown of glucose to pyruvate – cytosol • 2. Citric Acid Cycle (Kreb’s Cycle)– pyruvate derivative (acetyl CoA) to CO2 – Mitochondrial matrix • 3. Electron Transport Chain and Oxidative Phosphorylation – electrons from glycolysis + CAC + O2 to H2O – Inner mitochondrial membrane What is substrate level phosphorylation? • A mode of ATP synthesis when an enzyme transfers a phosphate group from a substrate molecule to ADP. 1. Glycolysis – “sugar breakdown” • In the cytoplasm, the bonds in glucose are rearranged producing pyruvate and releasing a small amount of free energy (ATP and NADH). Pyruvate is transferred from the cytoplasm to the mitochondria • Pyruvate cannot enter the Citric Acid Cycle • 2 Pyruvate 2 Acetyl Coenzyme A (CoA) – 2 CO2 is released – 2 NADH formed 2. Citric Acid Cycle – Krebs Cycle • Occurs in the Mitochondrial Matrix • Substrate Level Phosphorylation – Small amounts of ATP are made • Electrons are extracted from compounds and captured and stored by coenzymes – NAD – FAD NAD+ NADH • NAD+ - nicotinamide adenine dinucleotide is a coenzyme that transports electrons from glucose to the electron transport chain to make ATP • NAD+ is reduced (electrons are added) to NADH + H+ using the enzyme dehydrogenase (2 electrons and 2 protons, but one proton is released) 3. Electron Transport Chain • Oxidative Phosphorylation – lots of ATP • Occurs in the inner mitochondrial membrane • Electrons stored in NADH and FADH2 from glycolysis and the CAC are transported to the ETC • Oxygen is the final electron acceptor! Chemiosmosis (Fig 9.15) Chemiosmosis • Proteins carry electrons through the ETC while proton pumps pump H+ out into the cristae • The H+’s create a gradient • As H+’s pass through the enzyme ATP synthase, ATP is made Oxidative Phosphorylation • Draw the ETC & Chemiosmosis • Summarize how chemiosmosis makes ATP. • Refer to figure 9.15 Electron shuttles span membrane CYTOSOL MITOCHONDRION 2 NADH or 2 FADH2 2 NADH 2 NADH Glycolysis Glucose 2 Acetyl CoA 2 Pyruvate Citric acid cycle + 2 ATP + 2 ATP by substrate-level phosphorylation by substrate-level phosphorylation Maximum per glucose: Figure 9.16 6 NADH About 36 or 38 ATP 2 FADH2 Oxidative phosphorylation: electron transport and chemiosmosis + about 32 or 34 ATP by oxidative phosphorylation, depending on which shuttle transports electrons from NADH in cytosol Complete the chart: Process Where? Phosphorylation 1. Glycolysis Cytosol Substrate Level 2. Pyruvate Acetyl CoA Mitochondrial Matrix N/A 3. Citric Acid Cycle (Kreb’s) Mitochondrial Matrix Substrate Level 4. Electron Transport Chain (ETC) Inner Mitochondrial Membrane Oxidative TOTAL Cytosol + Mitochondria N/A Input Output Making ATP – Energy • Catabolic Pathways • Aerobic Respiration – O2 available – Exergonic – lots of energy – Glucose energy – mitochondria • Anaerobic Respiration = Fermentation - No O2 available – Only partially degrades sugars – Not a lot of energy – cytosol Fermentation = anaerobic respiration Glucose CYTOSOL Pyruvate No O2 present Fermentation O2 present Cellular respiration MITOCHONDRION Ethanol or lactate Acetyl CoA Citric acid cycle Fermentation = anaerobic respiration • No O2 present (no electronegative pull exists from oxygen – NO ETC) • Glycolyis and NAD+ regeneration – If NAD+ is not regenerated ATP cannot be produced Alcoholic Fermentation • Glycolysis – glucose 2 pyruvates • 2 Pyruvate Ethanol + CO2 • Ethanol (Ethyl alcohol) accepts electrons from NADH therefore regenerating NAD+ • Used by bakers and brewers – yeast (fungal) cells ferment • Many bacteria ferment Lactic Acid Fermentation • Glycolysis – glucose 2 pyruvate • 2 pyruvate 2 Lactate • Lactate accepts the electrons from NADH regenerating NAD+ • Fungi and bacteria • Human muscle cells – Anaerobic exercise Respiration vs. Fermentation • Respiration – – – – O2 Mitochondria Electron Acceptor is O2 ~36-38 ATP • Fermentation (anaerobic) – No O2 – Cytosol – Electron Acceptors are Ethanol or Lactate – 2 ATP Heterotrophs don’t eat just glucose Proteins • Proteins, Lipids and Carbs may enter the process of respiration at various locations • Glucose provides the most direct ATP Amino acids Carbohydrates Sugars Glycolysis Glucose Glyceraldehyde-3- P NH3 Pyruvate Acetyl CoA Citric acid cycle Figure 9.19 Oxidative phosphorylation Fats Glycerol Fatty acids