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Water behind a dam represents _____ energy. A) Kinetic B) Electrical C) Potential D) Heat E) Electromagnetic The “powerhouse of the cell” is the_________. A) Nucleus. B) Mitochondrion. C) Golgi complex. D) Ribosome. E) None of these Mitochondrial structure review Cellular respiration provides us with the energy we use Slow-twitch muscles have more mitochondria than fast-twitch Cellular Respiration All Living Things Require and Consume Energy • Ultimate source of energy for all life on earth is the sun • We get our energy from food Aerobic respiration of glucose is the most basic means for cells to acquire energy C6H12O6(s) + 6O2(g) 6CO2(g)+ 6H2O(l) This is a combustion reaction Combustion is a kind of redox reaction Respiration interacts with photosynthesis in the recycling of carbon Respiration at the cellular level necessitates our breathing The more our cells respire, the more oxygen we need Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with glucose: C6H12O6(s) + 6O2(g) 6CO2(g)+ 6H2O(l) + Energy (ATP + heat) Respiration is a REDOX reaction Oxidation-Reduction Reactions • • • • Cellular respiration is a redox reaction Involves the exchange of electrons Oxidation- the loss of electrons Reduction- the gain of electrons (reduction of charge • Na + Cl Na+ + Cl• Which is oxidized? Which is reduced? Redox does not require complete loss or gain of electrons Products Reactants becomes oxidized CH4 2 Oreduced +becomes 2 CO2 + Energy + 2 H2O becomes reduced becomes reduced Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxide Water During cellular respiration, glucose is oxidized and oxygen is reduced becomes oxidized C6H12O6 + 6O2 6CO2 + 6H2O + Energy becomes reduced Electrons bound to more electronegative atoms are lower in energy • The energy heirarchy of carbon bonds: CH4 CH3OH CH2O HCOOH CO2 Electrons in reduced molecules have higher energy than those in oxidized molecules Aerobic respiration of glucose is the most basic means for cells to acquire energy C6H12O6(s) + 6O2(g) 6CO2(g)+ 6H2O(l) The cell must control this reaction Oxidation is the ______, and reduction is the __________. A) gain of electrons . . . loss of electrons B) loss of electrons . . . gain of electrons C) loss of oxygen . . . gain of oxygen D) gain of oxygen . . . loss of oxygen E) gain of protons . . . loss of protons The Stages of Cellular Respiration: A Preview • Cellular respiration has three stages: – Glycolysis – The citric acid cycle (a.k.a. the Krebs cycle) – Oxidative phosphorylation (using the electron transport chain) LE 9-6_1 Glycolysis Pyruvate Glucose Cytosol Mitochondrion ATP Substrate-level phosphorylation LE 9-6_2 Glycolysis Pyruvate Glucose Cytosol Citric acid cycle Mitochondrion ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation LE 9-6_3 Electrons carried via NADH and FADH2 Electrons carried via NADH Glycolysis Pyruvate Glucose Cytosol Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis Mitochondrion ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation ATP Oxidative phosphorylation Overview of respiration • Glycolysis: Glucose is split, 2 pyruvates are formed, a little ATP is gained (by substrate-level phosporylation) • The Citric Acid Cycle: Redox molecules NAD+ and FAD are charged up, a little ATP is gained • Oxidative phosphorylation: Lots of ATP is made by ATP synthase Processes important to respiration • Substrate-level phosphorylation to form ATP • Recycling of the Redox molecules NAD+ and FAD to carry electrons to the etransport chain • The electron transport chain, which helps generate much ATP Substrate-level phosphorylation Making ATP by taking a phosphate from something and sticking it onto an ADP Recycling of NAD+ e The transport chain generates a proton gradient Step 1: Glycolysis In: 1 glucose, 2 NAD+ Out: 2 ATP (net), 2NADH, 2 pyruvate Glycolysis converts glucose to pyruvate • Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate • Glycolysis occurs in the cytoplasm and has two major phases: – Energy investment phase – Energy payoff phase Animation: Glycolysis Overview of Glycolysis • • • • 10- step process Glucose (6C) 2 Pyruvate ( 3 C ea.) 2 ATPs net profit 2 NAD+’s are charged LE 9-9a_1 Glucose ATP Hexokinase ADP Glucose-6-phosphate Glycolysis Citric acid cycle ATP ATP Oxidation phosphorylation ATP LE 9-9a_2 Glucose ATP Hexokinase ADP Glucose-6-phosphate Phosphoglucoisomerase Fructose-6-phosphate ATP Phosphofructokinase ADP Fructose1, 6-bisphosphate Aldolase Isomerase Dihydroxyacetone phosphate Glyceraldehyde3-phosphate Glycolysis Citric acid cycle ATP ATP Oxidation phosphorylation ATP LE 9-9b_1 2 NAD+ Triose phosphate dehydrogenase 2 NADH + 2 H+ 1, 3-Bisphosphoglycerate 2 ADP Phosphoglycerokinase 2 ATP 3-Phosphoglycerate Phosphoglyceromutase 2-Phosphoglycerate LE 9-9b_2 2 NAD+ Triose phosphate dehydrogenase 2 NADH + 2 H+ 1, 3-Bisphosphoglycerate 2 ADP Phosphoglycerokinase 2 ATP 3-Phosphoglycerate Phosphoglyceromutase 2-Phosphoglycerate 2 H2O Enolase Phosphoenolpyruvate 2 ADP Pyruvate kinase 2 ATP Pyruvate Energetics of Glycolysis Concept 9.3: The citric acid cycle completes the energyyielding oxidation of organic molecules • Before the citric acid cycle can begin, pyruvate must be converted to acetyl CoA, which links the cycle to glycolysis Before the citric acid cycle, pyruvate is fastened to Co-Enzyme A Step 2: Citric Acid cycle In: Acetyl CoA, NAD+, FAD, ADP Out: CO2, NADH, FADH, some ATP • In the citric acid cycle, electrons are ripped from carbon onto the redox molecules NAD+ and FAD • All carbon is converted to CO2 • A little bit of ATP is generated • The citric acid cycle, also called the Krebs cycle, takes place within the mitochondrial matrix • The cycle oxidizes organic fuel derived from pyruvate, generating one ATP, 3 NADH, and 1 FADH2 per turn • The citric acid cycle has eight steps, each catalyzed by a specific enzyme LE 9-11 Pyruvate (from glycolysis, 2 molecules per glucose) CO2 NAD+ Glycolysis Citric acid cycle ATP ATP Oxidation phosphorylation CoA NADH + H+ Acetyl CoA CoA CoA Citric acid cycle FADH2 2 CO2 3 NAD+ 3 NADH + 3 H+ FAD ADP + P i ATP ATP LE 9-12_4 Glycolysis Citric acid cycle ATP ATP Oxidation phosphorylation ATP Acetyl CoA NADH + H+ H2O NAD+ Oxaloacetate Malate Citrate Isocitrate CO2 Citric acid cycle H2O NAD+ NADH + H+ Fumarate a-Ketoglutarate FADH2 NAD+ FAD Succinate GTP GDP ADP ATP Pi Succinyl CoA NADH + H+ CO2 Step 3: Oxidative Phosphorylation In which the electron transport chain generates a proton gradient, and ATP synthase makes tons of ATP Oxidative phosphorylation • Electron-carrying redox molecules (NADH and FADH2) transfer their electrons to the e- transport chain • The e- transport chain uses the electrons to create a proton gradient across the inner mitochondrial membrane • ATP synthase uses the potential energy in the proton gradient to convert much ADP into ATP LE 9-13 NADH 50 Free energy (G) relative to O2 (kcal/mol) FADH2 40 FMN I Multiprotein complexes FAD Fe•S II Fe•S Q III Cyt b 30 Fe•S Cyt c1 Glycolysis Citric acid cycle ATP ATP Oxidative phosphorylation: electron transport and chemiosmosis IV Cyt c Cyt a Cyt a3 20 10 0 2 H+ + 1/2 O2 H2O ATP The electron transport chain uses electrons to generate a proton gradient H+ H+ H+ Protein complex Intermembrane space H+ H+ H+ H+ Electron carrier H+ H+ ATP synthase Inner mitochondrial membrane FADH2 Electron flow NADH Mitochondrial matrix FAD NAD+ H+ 1 2 O2 + 2 H+ H+ H+ H2O Electron Transport Chain OXIDATIVE PHOSPHORYLATION ADP + P ATP H+ Chemiosmosis Some poisons can disrupt e- transport • The energy stored in a H+ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis • The H+ gradient is referred to as a protonmotive force, emphasizing its capacity to do work Animation: Fermentation Overview LE 9-14 INTERMEMBRANE SPACE H+ H+ H+ H+ H+ H+ A rotor within the membrane spins as shown when H+ flows past it down the H+ gradient. H+ A stator anchored in the membrane holds the knob stationary. A rod (or “stalk”) extending into the knob also spins, activating catalytic sites in the knob. H+ ADP + P ATP i MITOCHONDRAL MATRIX Three catalytic sites in the stationary knob join inorganic phosphate to ADP to make ATP. An Accounting of ATP Production by Cellular Respiration • During cellular respiration, most energy flows in this sequence: glucose NADH electron transport chain proton-motive force ATP • About 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 38 ATP LE 9-16 Electron shuttles span membrane CYTOSOL 2 NADH Glycolysis Glucose 2 Pyruvate MITOCHONDRION 2 NADH or 2 FADH2 2 NADH 2 Acetyl CoA 6 NADH Citric acid cycle + 2 ATP + 2 ATP by substrate-level phosphorylation by substrate-level phosphorylation Maximum per glucose: About 36 or 38 ATP 2 FADH2 Oxidative phosphorylation: electron transport and chemiosmosis + about 32 or 34 ATP by oxidation phosphorylation, depending on which shuttle transports electrons form NADH in cytosol During cellular respiration, NADH A) is converted to NAD+ by an enzyme called dehydrogenase. B) is chemically converted into ATP. C) is reduced to form NAD+. D) delivers its electron load to the electron transport chain. E) None of the choices are correct. Oxygen is the final e- resting place in the chain Human cells can do glycolysis faster than human lungs can take in oxygen Q: What happens if there is not enough oxygen? A: It depends on what kind of creature you are… Without O2, yeast make alcohol Humans make lactic acid instead of ethanol Lactic Acid in muscles creates a burning sensation • Overworked muscles can become anoxic • In low oxygen environments, pyruvate is converted to lactate to regenerate NAD+ • Lactic acid causes great suffering LE 9-17a 2 ADP + 2 P i Glucose 2 ATP Glycolysis 2 Pyruvate 2 NAD+ 2 Ethanol Alcohol fermentation 2 NADH + 2 H+ 2 CO2 2 Acetaldehyde LE 9-17b 2 ADP + 2 P i Glucose 2 ATP Glycolysis 2 NAD+ 2 NADH + 2 H+ 2 CO2 2 Pyruvate 2 Lactate Lactic acid fermentation Fermentation and Cellular Respiration Compared • Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate • The processes have different final electron acceptors: an organic molecule (such as pyruvate) in fermentation and O2 in cellular respiration • Cellular respiration produces much more ATP LE 9-18 Glucose CYTOSOL Pyruvate No O2 present Fermentation O2 present Cellular respiration MITOCHONDRION Ethanol or lactate Acetyl CoA Citric acid cycle The Evolutionary Significance of Glycolysis • Glycolysis occurs in nearly all organisms • Glycolysis probably evolved in ancient prokaryotes before there was oxygen in the atmosphere Glycolysis and the citric acid cycle connect to many other metabolic pathways • Gycolysis and the citric acid cycle are major intersections to various catabolic and anabolic pathways Metabolism can build up, or break down LE 6-15 ATP needed to drive biosynthesis ATP CITRIC ACID CYCLE GLUCOSE SYNTHESIS Acetyl CoA Pyruvate G3P Glucose Amino groups Amino acids Proteins Fatty acids Glycerol Fats Cells, tissues, organisms Sugars Carbohydrates The Versatility of Catabolism • Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration • Glucose- 4 calories/gram • Proteins- 4 calories/gram • Fats- 9 calories/gram • Which of the following processes produces the most ATP per molecule of glucose oxidized? A) aerobic respiration B) anaerobic respiration C) alcoholic fermentation D) lactic acid fermentation E) All produce approximately the same amount of ATP per molecule of glucose