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Lactic Acid Fermentation, Pyruvate Is Reduced Directly by NADH to Form Lactate Without the Release Of BIOLOGY 101 CHAPTER 9: Cellular Respiration - Fermentation: Life is Work An Introduction to Metabolism: Energy of Life 8.3 ATP powers cellular work by coupling exergonic reactions to endergonic reactions • Cells manage their energy resources to do this work by energy coupling, using an exergonic process to drive an endergonic one. • ATP is responsible for mediating most energy coupling in cells, and in most cases it acts as the immediate source of energy that powers cellular work • ATP is the energetic link between Exergonic and Endergonic reactions! An Introduction to Metabolism: Energy of Life 8.3 ATP powers cellular work by coupling exergonic reactions to endergonic reactions • Cells manage their energy resources to do this work by energy coupling, using an exergonic process to drive an endergonic one. • ATP is responsible for mediating most energy coupling in cells, and in most cases it acts as the immediate source of energy that powers cellular work • ATP is the energetic link between Exergonic and Endergonic reactions! An Introduction to Metabolism: Energy of Life 8.3 ATP powers cellular work by coupling exergonic reactions to endergonic reactions • How is most of a cell’s ATP generated? Cellular Respiration - Fermentation: Life is Work CONCEPTS: • 9.1 Catabolic pathways yield energy by oxidizing organic fuels o 9.2 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate o 9.3 After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules o 9.4 During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis • 9.5 Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen • 9.6 Glycolysis and the citric acid cycle connect to many other metabolic pathways What is important about each of these processes? Cellular Respiration - Fermentation: Life is Work 9.1 Catabolic pathways yield energy by oxidizing organic fuels • Catabolic metabolic pathways release energy stored in complex organic molecules. o Electron transfer plays a major role in these pathways. • Organic compounds possess potential energy as a result of the arrangement of electrons in the bonds between their atoms. o Enzymes regulate these pathways by catalyzing the systematic degradation of organic molecules that are rich in energy to simpler waste products that have less energy. o Some of the released energy is used to do work; the rest is dissipated as heat or lost to Entropy • One type of catabolic process, fermentation, leads to the partial degradation of sugars without the use of oxygen. o This is NOT an efficient transformation of energy Cellular Respiration - Fermentation: Life is Work 9.1 Catabolic pathways yield energy by oxidizing organic fuels • A more efficient and widespread catabolic process, aerobic respiration, consumes oxygen as a reactant to complete the breakdown of a variety of organic molecules. o Most eukaryotic and many prokaryotic organisms can carry out aerobic respiration. o Some prokaryotes use compounds other than oxygen as reactants in a similar process called anaerobic respiration. o Although cellular respiration technically includes both aerobic and anaerobic processes, the term is commonly used to refer only to the aerobic process. Cellular Respiration - Fermentation: Life is Work 9.1 Catabolic pathways yield energy by oxidizing organic fuels Tracking Electrons! • We will be tracing the flow of electrons through the process of generating ATP from Glucose o Molecules that ACCEPT electrons are said to be “Reduced” and the process is called reduction o Molecules that LOSE electrons are said to be “Oxidized” and the process is called oxidation. o As electrons flow between molecules in mitochondria, molecules will either be oxidized or reduced Cellular Respiration - Fermentation: Life is Work 9.1 Catabolic pathways yield energy by oxidizing organic fuels BACKGROUND: • It can be observed that a flow of particles can provide a source of energy • The electrons start out in simple sugars (glucose) and end up being dumped on to very important Electron Acceptor Molecules. The most important is O2, and that is why we breathe! • In our cells, electrons ‘travel’ inside Hydrogen atoms. They cannot ‘travel’ free (just as electrons) so this is the easiest way for them to move from molecule to molecule (in Hydrogen atoms) o An electron carrier molecule NAD+, is used to transport electrons in respiration ✓ It is represented as NAD+ in its oxidized (empty) form ✓ It is represented as NADH in its reduced (full) form Cellular Respiration - Fermentation: Life is Work O2 NAD+ Mitochondria H2O Glucose NADH Cellular Respiration - Fermentation: Life is Work Glucose is packed full of high energy electrons Glucose Cellular Respiration - Fermentation: Life is Work NAD+ can carry the high energy electrons away from glucose NAD+ Glucose Cellular Respiration - Fermentation: Life is Work When NAD+ is reduced, it becomes NADH, which can transport high energy electrons to locations in Mitochondria Glucose NADH Cellular Respiration - Fermentation: Life is Work When NAD+ is reduced, it becomes NADH, which can transport high energy electrons to locations in Mitochondria Mitochondria Glucose NADH Cellular Respiration - Fermentation: Life is Work Now the high energy electrons are located inside the mitochondria and NAD+ has been regenerated NAD+ Mitochondria Glucose Cellular Respiration - Fermentation: Life is Work As more glucose arrives, NAD+ is available to carry the electrons away from glucose NAD+ Mitochondria Glucose Glucose Cellular Respiration - Fermentation: Life is Work NAD+ is reduced and NADH now has the electrons Mitochondria Glucose NADH cannot release its electrons because Glucose NADH the mitochondria is already full of electrons Cellular Respiration - Fermentation: Life is Work More glucose arrives, but there is no NAD+ to remove the high energy electrons Mitochondria Glucose Glucose NADH cannot release its electrons because Glucose NADH the mitochondria is already full of electrons Cellular Respiration - Fermentation: Life is Work More glucose arrives, but there is no NAD+ to remove the high energy electrons Mitochondria Glucose Glucose Glucose NADH cannot release its electrons because Glucose NADH the mitochondria is already full of electrons Cellular Respiration - Fermentation: Life is Work More glucose arrives, but there is no NAD+ to remove the high energy electrons Mitochondria Glucose Glucose Glucose Glucose NADH cannot release its electrons because Glucose NADH the mitochondria is already full of electrons Cellular Respiration - Fermentation: Life is Work A MOLECULE IS NEEDED TO REMOVE ELECTRONS FROM THE SYSTEM Mitochondria Glucose Glucose Glucose Glucose Glucose NADH Cellular Respiration - Fermentation: Life is Work Oxygen will remove electrons from the system O2 Mitochondria Glucose Glucose Glucose Glucose Glucose NADH Cellular Respiration - Fermentation: Life is Work As this occurs, ADP is transformed to ATP O Oxygen will remove electrons from the system 2 ADP Mitochondria Glucose Glucose Glucose Glucose Glucose NADH Cellular Respiration - Fermentation: Life is Work As this occurs, ADP is transformed to ATP The flow of electrons drives the production of ATP ADP Mitochondria Glucose Glucose Glucose ATP Glucose H2O Glucose NADH Cellular Respiration - Fermentation: Life is Work Mitochondria Glucose Glucose Glucose ATP Glucose H2O Glucose NADH Energy is now trapped in ATP and low energy electrons are now in water Cellular Respiration - Fermentation: Life is Work NADH passes its electrons to structures inside O2 mitochondria and NAD+ is regenerated ADP NAD+ Mitochondria Glucose Glucose Glucose ATP Glucose H2O Glucose Cellular Respiration - Fermentation: Life is Work NOTE: OXYGEN IS NEEDED TO KEEP O ELECTRONS FLOWING 2 NAD+ Mitochondria Glucose Glucose Glucose ATP Glucose Glucose NADH Cellular Respiration - Fermentation: Life is Work 9.1 Catabolic pathways yield energy by oxidizing organic fuels • Aerobic respiration is similar in broad principle to the combustion of gasoline in an automobile engine after oxygen is mixed with hydrocarbon fuel. o Food provides the fuel for respiration. The exhaust is carbon dioxide and water. Cellular Respiration - Fermentation: Life is Work 9.1 Catabolic pathways yield energy by oxidizing organic fuels • The overall catabolic process is: organic compounds + O2 CO2 + H2O + energy (ATP + heat) • Carbohydrates, fats, and proteins can all be used as the fuel, but it is most useful to consider glucose: C6H12O6 + 6O2 6CO2 + 6H2O + energy (ATP + heat) Cellular Respiration - Fermentation: Catabolic pathways yield energy by oxidizing organic fuels 9.1 Redox reactions release energy when electrons move closer to electronegative atoms. • Catabolic pathways transfer the electrons stored in food molecules, releasing energy that is used to synthesize ATP. • Reactions that result in the transfer of one or more electrons (e−) from one reactant to another are oxidation-reduction reactions, or redox reactions. o The loss of electrons from a substance is called oxidation. o The addition of electrons to another substance is called reduction. ✓ Adding electrons is called reduction because negatively charged electrons added to an atom reduce the amount of positive charge of that atom. • The Oxidation and Reduction of molecules is a paired process. One cannot occur without the other Cellular Respiration - Fermentation: Catabolic pathways yield energy by oxidizing organic fuels 9.1 Organic fuel molecules are oxidized
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