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Harvesting stored energy • Energy is stored in organic molecules • carbohydrates, fats, proteins • Heterotrophs eat these organic molecules food • digest organic molecules to get… • raw materials for synthesis • fuels for energy • controlled release of energy • “burning” fuels in a series of step-by-step enzyme-controlled reactions Figure 9.2 Light energy ECOSYSTEM Photosynthesis in chloroplasts CO2 H2O Cellular respiration in mitochondria ATP Heat energy Organic O2 molecules ATP powers most cellular work Living economy • Fueling the body’s economy • eat high energy organic molecules • food = carbohydrates, lipids, proteins, nucleic acids • break them down • digest = catabolism • capture released energy in a form the cell can use • Need an energy currency • a way to pass energy around • need a short term energy storage molecule Whoa! Hot stuff! ATP ATP • Adenosine TriPhosphate • modified nucleotide • nucleotide = adenine + ribose + Pi AMP • AMP + Pi ADP • ADP + Pi ATP • adding phosphates is endergonic How efficient! Build once, use many ways high energy bonds How does ATP store energy? ADP AMP ATP I think he’s a bit unstable… don’t you? O– O– O– –O – –O – OP P –O OP OP O– O O O • Each negative PO4 more difficult to add • a lot of stored energy in each bond • most energy stored in 3rd Pi • 3rd Pi is hardest group to keep bonded to molecule • Bonding of negative Pi groups is unstable • spring-loaded • Pi groups “pop” off easily & release energy Instability of its P bonds makes ATP an excellent energy donor How does ATP transfer energy? O– O– O– –OP –O – –O – OP OP O– O O O ATP ADP O– –OP O– + O • ATP ADP • releases energy • ∆G = -7.3 kcal/mole • Fuel other reactions • Phosphorylation • released Pi can transfer to other molecules • destabilizing the other molecules • enzyme that phosphorylates = “kinase” 7.3 energy ATP / ADP cycle Can’t store ATP cellular good energy donor, not good energy storage respiration ATP 7.3 kcal/mole too reactive transfers Pi too easily only short term energy ADP + Pi storage carbohydrates & fats are A working muscle recycles over long term energy storage 10 million ATPs per second Whoa! Pass me the glucose (and O2)! How do we harvest energy from fuels? • Digest large molecules into smaller ones • break bonds & move electrons from one molecule to another • as electrons move they “carry energy” with them • that energy is stored in another bond, released as heat or harvested to make ATP loses e- gains e- + oxidized reduced + + eoxidation e- – ereduction redox Oxidation & reduction • Oxidation • Reduction • adding O • removing H • loss of electrons • releases energy • exergonic • removing O • adding H • gain of electrons • stores energy • endergonic oxidation C6H12O6 + 6O2 6CO2 + 6H2O + ATP reduction Moving electrons in respiration • Electron carriers move electrons by shuttling H atoms around • NAD+ NADH (reduced) • FAD+2 FADH2 (reduced) NAD+ nicotinamide Vitamin B3 niacin O– O–P –O O phosphates O– O–P –O O NADH O H C N+ + adenine ribose sugar H H NH2 C reduction O– – –O oxidation O P O O– O–P –O O carries electrons as H O a reduced molecule N+ NH2 How efficient! Build once, use many ways Overview of cellular respiration • 4 metabolic stages • Anaerobic respiration 1. Glycolysis • respiration without O2 • in cytosol • Aerobic respiration • respiration using O2 • in mitochondria 2. Pyruvate oxidation 3. Citric Acid (Krebs) cycle 4. Electron transport chain C6H12O6 + 6O2 ATP + 6H2O + 6CO2 (+ heat) • Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration (Energy stored in NADH and FADH2 is used to produce ATP) © 2011 Pearson Education, Inc. • A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation • For each molecule of glucose degraded to CO2 and water by respiration, the cell makes up to 32 molecules of ATP © 2011 Pearson Education, Inc. Concept 9.2: Glycolysis harvests chemical energy by oxidizing 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 • Glycolysis occurs whether or not O2 is present © 2011 Pearson Education, Inc. Glycolysis • Breaking down glucose • “glyco – lysis” (splitting sugar) glucose pyruvate 2x 3C 6C • ancient pathway which harvests energy • where energy transfer first evolved • transfer energy from organic molecules to ATP • still is starting point for ALL cellular respiration • but it’s inefficient • generate only 2 ATP for every 1 glucose • occurs in cytosol That’s not enough ATP for me! In the cytosol? Why does that make evolutionary sense? Evolutionary perspective • Prokaryotes • first cells had no organelles Enzymes of glycolysis are “well-conserved” • Anaerobic atmosphere • life on Earth first evolved without free oxygen (O2) in atmosphere • energy had to be captured from organic molecules in absence of O2 • Prokaryotes that evolved glycolysis are ancestors of all modern life • ALL cells still utilize glycolysis You mean we’re related? Do I have to invite them over for the holidays? endergonic invest some ATP exergonic harvest a little ATP & a little NADH net yield 2 ATP 2 NADH If you get bored……but you don’t need to know this!!! Concept 9.3: After pyruvate is oxidized, the citric acid cycle completes the energyyielding oxidation of organic molecules • In the presence of O2, pyruvate enters the mitochondrion (in eukaryotic cells) where the oxidation of glucose is completed © 2011 Pearson Education, Inc. The Citric Acid Cycle • The citric acid cycle, also called the Krebs cycle, completes the break down of pyruvate to CO2 • The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn © 2011 Pearson Education, Inc. Figure 9.12-8 Acetyl CoA CoA-SH NADH + H H2O 1 NAD 8 Oxaloacetate 2 Malate Citrate Isocitrate NAD Citric acid cycle 7 H2O Fumarate NADH 3 + H CO2 CoA-SH -Ketoglutarate 4 6 CoA-SH 5 FADH2 NAD FAD Succinate GTP GDP ADP ATP Pi Succinyl CoA NADH + H CO2