BIOL217 F24 Topic07 Cellular Respiration PDF

BIOL 217 Topic 07 Fall 2024 Learning Objectives – Topic 07 Cellular Respiration and Fermentation – Chapter 9 Understand cellular energy, and how catabolic processes release energy from food Understand how redox reactions work, including transfer of electrons and oxidation / reduction, an...

BIOL 217 Topic 07 Fall 2024 Learning Objectives – Topic 07 Cellular Respiration and Fermentation – Chapter 9 Understand cellular energy, and how catabolic processes release energy from food Understand how redox reactions work, including transfer of electrons and oxidation / reduction, and apply these to cellular metabolism Describe the major steps in cellular respiration: glycolysis, 2 Learning Objectives – Topic 07 Cellular Respiration and Fermentation – Chapter 9 Explain the importance of NAD+/NADH in cellular respiration and fermentation Explain how transport of electrons down the ETC is couple to the production of ATP by chemiosmosis Compare how fermentation (two types) differs from cellular respiration (aerobic and anaerobic respiration) 3  Obtaining cellular energy Cell requires energy from outside sources to do work Cellular work includes: Mechanical Chemical Transport Organisms obtain this energy by ingesting: Other animals Photosynthetic organisms 4 Figure 9.1  Energy flows and chemicals cycle Energy enters ecosystem as light Energy leaves as heat Chemical elements are recycled Ie) carbon and nitrogen cycles 5 Figure 1.9  Energy flows and chemicals cycle Photosynthesis generates O2 and organic molecules O2 and organic molecules are used in cellular respiration Cells use chemical energy stored in organic molecules to generate ATP, which powers work 6 Figure 9.2 Catabolic pathways yield energy by oxidizing organic fuels Catabolic pathways: release stored energy by breaking down complex molecules (fuel) Breaking down complex molecules releases electrons Processes are central to cellular respiration 7  Different catabolic pathways to produce ATP The breakdown of organic molecules is exergonic Releases potential energy in the bonds between atoms These molecules are known as fuels 1) Fermentation: A partial degradation of sugars that occurs without O2 Wine, cheese, beer, bread, etc 8 Tiburi (2016). https://cdn.pixabay.com/photo/2016/07/15/09/05/factory-1518504_1280.jpg  Different catabolic pathways to produce ATP 2) Aerobic respiration: Consumes organic molecules and O2, yielding ATP Performed by most eukaryotic cells and many prokaryotic cells Organic Compounds + Oxygen > Carbon dioxide + Water + Energy 9 Different catabolic pathways to produce ATP 3) Anaerobic respiration: Similar to aerobic respiration, but consumes compounds other than O2 (ie: NO3- or SO42-) Cellular respiration: Includes both aerobic and anaerobic respiration, but is often used to refer to aerobic respiration Carbohydrates, fats, and proteins are all consumed as fuel 10  In cellular respiration, electrons are transferred Transfer of electrons during chemical reactions releases energy stored in organic molecules This released energy is ultimately used to synthesize ATP Chemical reactions that transfer electrons between reactants are called oxidation- reduction reactions, or redox reactions 11 Victoria_rt (2020). https://cdn.pixabay.com/photo/2020/10/06/16/11/chemistry-5632654_1280.jpg  Redox Reactions The electron donor is called the reducing agent The electron receptor is called the oxidizing agent Some redox reactions do not transfer electrons, but change the electron sharing in covalent bonds 12 Figure 9.3  The Steps of Cellular Respiration Harvesting of energy from glucose has three stages 1. Glycolysis: Breaks down glucose into two molecules of pyruvate 2. The citric acid cycle: Completes the breakdown of glucose 3. Oxidative phosphorylation: Accounts for most of the ATP synthesis (~90% of ATP production) 13 Figure 9.UN05  Overview of Cellular Respiration 14 Figure 9.6  ATP production via phosphorylation Oxidative Phosphorylation: Powered by redox reactions of the electron transport chain ~90% of ATP production Substrate-Level Phosphorylation: Enzyme transfers phosphate group from substrate to ADP Fewer ATP produced, via glycolysis and the citric acid cycle For each glucose, cell makes up to 32 ATP molecules Modified Figure 9.16 15 Figure 9.7  Glycolysis – oxidizes glucose to pyruvate Sugar splitting Splits 1 glucose (1x6C) into 2 pyruvate (2x3C) Occurs in cytosol Occurs whether O2 is present or not Occurs in prokaryotic and eukaryotic cells Figure 9.UN06 16 Modified Figure 9.9  2 Major phases of Glycolysis Energy investment phase Cell expends energy (2 ATP) Energy payoff phase Cell produces 4 ATP via substrate level phosphorylation Net Production from 1 glucose: 2 Pyruvate 2 ATP 2 H2O 2 NADH + 2H+ 17 Figure 9.8  Electron Transport Chain (ETC) in mitochondria ETC is in the inner membrane (cristae) of mitochondria Most components are multi protein complexes in inner mitochondrial membrane Intermembrane Space Figure 6.17 Matrix 18 Modified Figure 9.15  Electron Transport Chain (ETC) Electrons are transferred from NADH or FADH2 to the ETC Carriers come from Glycolysis or CAC Electrons are passed through numerous proteins, ending with O2 Free Energy Diagram (most electronegative) 19 Figure 9.13  Electron Transport Chain (ETC) Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O Breaks the large free-energy drop from food to O2 into smaller steps Free Energy Diagram Releases energy in manageable amounts 20 Figure 9.13  Electron Transport Chain Electron carriers alternate between reduced and oxidized states as they accept and donate electrons Terminal electron acceptor: Oxygen, which is strongly electronegative, then forms H2O The ETC generates no ATP directly 21 Figure 9.13  If the ETC generates no ATP directly, how is ATP produced? The energy released as electrons are Intermembrane passed down the ETC: Space Pumps H+ from the mitochondrial matrix to the intermembrane space The ETC creates a higher [H+] in intermembrane space H+ then moves down its concentration gradient back across the membrane Passes through the protein complex Matrix ATP synthase 22 Figure 9.16  Chemiosmosis: The energy-coupling mechanism Chemiosmosis: the use of energy in a H+ gradient to drive cellular work H+ moves into binding sites on the rotor of ATP synthase Causes it to spin and catalyze phosphorylation of ADP + inorganic Phosphate > ATP 23 Figure 9.15  Chemiosmosis: The energy-coupling mechanism 1. H+ ions flow down concentration gradient 2. H+ ions enter binding sites in rotor, changing shape of subunit so rotor spins within membrane 3. Each H+ ion makes one spin before exiting via a channel into mitochondrial matrix 4. Spinning of rotor causes internal rod to spin 5. Spinning rod causes catalytic sites in the catalytic knob to produce ATP from ADP and Pi 24 Figure 9.15 Cellular Respiration Bioflix http://www.youtube.com/watch?v=q-fKQuZ8dco (2:55 – 4:10)  Oxidative Phosphorylation 25 Figure 9.16  An audit of ATP production by Cellular Respiration During cellular respiration, most energy flows in this sequence: Glucose → NADH or FADH2 → ETC → proton- motive force → ATP About 34% of the energy in a glucose molecule is transferred to ATP, making about 32 ATP The rest of the energy is lost as heat 26 Figure 9.17  An audit of ATP production by Cellular Respiration About 32 ATP: Depends on the electron shuttle used to bring electrons from cytosolic NADH (glycolysis) across mitochondrial membrane 27 Figure 9.17  Anaerobic Respiration Some prokaryotic organisms Has an electron transport chain, but does not use oxygen (O2) as final electron acceptor Therefore, does not produce water at end Other final electron acceptors are less electronegative than oxygen, and are less efficient at producing energy SO42- NO3- Pixabay (2017). Brown Surface Beside Body of Water in a Distant of Mountains Under White Clouds during Daytime. https://images.pexels.com/photos/163992/pexels-photo- 28 163992.jpeg?auto=compress&cs=tinysrgb&dpr=2&h=650&w=940  Fermentation After glycolysis, in presence of O2, cells use aerobic respiration Electronegative oxygen pulls electrons down ETC In absence of O2, this ETC will not operate Instead, glycolysis couples with fermentation to produce ATP ATP produced by glycolysis NAD+ replenished in fermentation 29 Figure 9.19  Fermentation and types of Fermentation Fermentation: Uses substrate-level phosphorylation instead of an ETC to generate ATP Consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis Two types are: Alcohol fermentation Lactic acid fermentation 30 Pixabay (2017). Close-Up of Wine and Fruits. https://images.pexels.com/photos/248413/pexels-photo-248413.jpeg?auto=compress&cs=tinysrgb&dpr=2&h=650&w=940  Alcohol Fermentation Pyruvate is converted to ethanol in two steps The first step releases CO2 from pyruvate The second step produces NAD+ and ethanol Alcohol fermentation by yeast is used in brewing, winemaking, and baking 31 Figure 9.18  Lactic Acid Fermentation Pyruvate is reduced by NADH, forming NAD+ and lactate as end products No release of CO2 Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt Lactic acid fermentation in human muscle cells: Generates ATP during strenuous exercise when O2 is scarce Cells switch from aerobic respiration to lactic acid fermentation 32 Figure 9.18  Comparing Fermentation with Anaerobic and Aerobic Respiration All use glycolysis to oxidize glucose and harvest the chemical energy of food Net ATP = 2 NAD+ is the oxidizing agent that accepts electrons during glycolysis 33 Modified Figure 9.18  Comparing Fermentation with Anaerobic and Aerobic Respiration Different mechanisms for oxidizing NADH to NAD+: In fermentation, an organic molecule (such as pyruvate or acetaldehyde) acts as a final electron acceptor In cellular respiration, electrons are transferred to the ETC Fermentation produces 2 ATP per glucose molecule Cellular respiration produces up to 32 ATP per glucose molecule Up to 2 ATP / glucose 34 Figure 9.19 32 ATP / glucose  Glycolysis during evolution Glycolysis is shared by prokaryotic and eukaryotic cells, regardless of oxygen presence This pathway occurs in the cytosol Does not require the membrane-bound organelles of eukaryotic cells Early prokaryotes likely used glycolysis to produce ATP before O2 accumulated in the atmosphere 35 Figure 9.6  Energy from multiple sources Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration Carbohydrates Proteins Fats 36 Figure 9.19