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How Cells Harvest Energy Chapter 9 We EAT sunlight energy trapped in arrangement of atoms CELLULAR RESPIRATION why do we need oxygen? energy Breathing by-product of photosynthesis? • Cellular Energy Harvest • Cellular Respiration – Glycolysis – Oxidation of Pyruvate – Krebs Cycle – Electron Transport Chain • Catabolism of Protein and Fat • Fermentation • Evolution of Metabolism burning fuel in the car •Organic compounds + O2 -> CO2 + H2O + Energy HEAT •Catabolic pathways release energy Autotrophs self feeders use photosynthesis (usually) to make their own food produce organic molecules from CO2 ALSO source for all nonautotrophic food! • Heterotrophs (us) consumers of biosphere – feed on • plants and others • dead organisms (feces, fallen leaves) – dependent on photoautotrophs for: – food – oxygen Cellular Respiration • Cells harvest energy • break chemical bonds and shift electrons OXIDATION OF GLUCOSE – GLUCOSE LOSES ELECTRONS (also protons ie hydrogen) – aerobic respiration - final electron acceptor is oxygen – anaerobic respiration - final electron acceptor is inorganic molecule (not oxygen) – fermentation - final electron acceptor is an organic molecule LIFE IS A LOT OF WORK! •Carbohydrates, fats, and proteins - all fuel •traditional - glucose •C6H12O 6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP + heat) •The catabolism of glucose is exergonic •delta G = 686 Kcal per mole of glucose. •positive or negative? •WASTE PRODUCTS HAVE LESS ENERGY • Remember Chemical reactions - exergonic or endergonic - based on free energy Do these products have more or less energy? • SPONTANEOUS (less energy, releases heat) Overall reaction: glucose + oxygen -> carbon dioxide + water + energy C6H12O6 + 6O2 6CO2 + 6H2O + energy how could this be measured in the lab? ATP • Adenosine Triphosphate • energy currency – drive movement – drive endergonic reactions • ATP Energy Currency : • adenosine triphosphate • nucleotide – nitrogenous base (adenine) – sugar (ribose) – three phosphate groups Figure 8.14a ATP •phosphate bonds –covalent, but weak - each has negative charge •repulsion contributes to instability – Negatives repel – Phosphates are negative – ATP (three phosphates), ADP (two phosphates) – Linking them requires overcoming repulsion Requires energy – ATP from ADP and a third phosphate requires energy (endergonic) – Releasing phosphate from ATP generates energy (exergonic) • bonds between phosphate groups broken by hydrolysis – Hydrolysis forms adenosine diphosphate – – [ATP -> ADP + Pi] – releases 7.3 Kcal of energy per mole of ATP – delta G is -13 kcal/mol Cell membrane •How IT WORKS IN muscle cells extracellular Enzyme Calcium ions –Calcium ions move to enzyme ATP binding site Ca++ Ca++ –ATP splits -ADP and phosphate –energy transfers phosphate onto protein ATP ADP Ca++ Cytosol intracellualr P P – –shape change drives calcium across membrane P P biochemical pathways Ca++ •ATP: Important Energy Storage Molecule energy stored as phosphate bond in ATP 3rd phosphate group added to ADP using energy from food energy IN p p p p energy released when phosphate bond broken ATP energy OUT energy hill p P+ p ADP p P+ p p ADP which is exergonic? enderogonic? but we only have about .5 - 3 min worth of ATP stored! Home runs and creatine? Creatine donates phosphate group! creatine – natural amino acid (not protein) C4H10N3 O5P (liver, kidney) Lots in muscle, cardiovascular tissues increases phosphocreatine -> ATP “reservoir” for ATP production 1 g diet; 1 g synthesized high intensity exercise (baseball) • transfer of phosphate group from ATP phosphorylation Substrate level phosphorylation – changes shape - work (transport, mechanical, or chemical) – returns to alternate shape MUSCLE-RECYCLES 10 MILLION ATP/SEC Also oxidative phosphyloration • Uses proton gradient to produce ATP • What are protons? H + • Our cells do both redox reactions transfer electron(s) from one reactant to another oxidation-reduction reactions loss of electrons - oxidation (degrades, catabolic – ENERGY OUT) \addition of electrons – reduction (energy IN, anabolic) Hydrogen, electrons NAD is a Cofactor (co enzyme, organic) Na + Cl Na+ Cl- salt - redox reaction *Na is oxidized -the reducing agent *Cl is reduced – the oxidizing agent (Cl charge is reduced - drops from 0 to -1) electron donor (sodium) - reducing agent electron recipient (cloride) - oxidizing agent need both donor and acceptor Oxygen - potent oxidizing agent (it is reduced!) CH4 + 2O2 CO2 + 2H2O *CH4 is oxidized *O2 is reduced *oxidation often involves the loss of H Importance of electrons *key role in atom’s reactivity *CR - Transfer of e- through a series of steps releases energy the cell can use WHY SMALL STEPS? - HEAT cellular respiration – series of redox • glucose is oxidized, releasing energy (oxidation -loses electrons) C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy (including heat) • oxygen is reduced (gains electrons) Hypoxia Shock Altitude sickness Blood loss Sepsis Systemic inflammation Path of e- in cellular respiration: food NADH e- transport chain oxygen Oxidation C6H12O6 + 6O2 6CO2 + 6H2O + energy Reduction * happens over a series of steps that involve special molecules called electron transporters • Electron Carrier Molecules Shuttle Electrons – Most important electron carrier is NAD+. COFACTOR NAD+ - oxidizing agent, accepts a hydrogen atom and TWO electrons, becoming NADH – NADH can carry electrons down energy hill on to another acceptor (also FAD/FADH) – Enzymes coordinate these transfers. - - NAD+ empty NADH loaded + NAD + + H + - H H proton NAD+ empty NAD oxidized NAD - + - - H reduced + + H Electron loss accompanied by protons (hydrogen ion) “dehydrogenation” - - 4 stages of cellular respiration 1.Glycolysis 2.Pryuvate Oxidation 3.Krebs cycle 4.Electron transport chain *net result of the 4 stages is about 36 ATP per glucose molecule Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cytoplasm Glucose NADH Glycolysis ATP Pyruvate Pyruvate oxidation AcetylCoA NADH NADH Krebs cycle CO2 Intermembrane space Mitochondrial matrix CO2 ATP FADH2 H2 O eMitochondrion ATP NAD+ and FAD Electron transport chain Inner mitochondrial membrane •cellular respiration uses oxygen as a reactant to breakdown organic molecules •Most occurs in “matrix” of mitochondria •BUT 1st step (glycolysis) occurs in cytoplasm (before mitochondria) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. OVERVIEW OF GLYCOLYSIS 1 6-carbon glucose (Starting material) 2 ATP P P 6-carbon sugar diphosphate 2 3 P P ENERGY IN!!!!!! P 6-carbon sugar diphosphate SOME ENERGY OUT! P 3-carbon sugar 3-carbon sugar phosphate phosphate P NADH 2 ATP Priming reactions. Priming reactions. Glycolysis begins with the addition of energy. Two highenergy phosphates from two molecules of ATP are added to the six-carbon molecule glucose, producing a six-carbon molecule with two phosphates. 3-carbon pyruvate Cleavage reactions. Then, the six-carbon molecule with two phosphates is split in two, forming two three-carbon sugar phosphates. P 3-carbon sugar 3-carbon sugar phosphate phosphate NADH 2 ATP 3-carbon pyruvate Energy-harvesting reactions. Finally, in a series of reactions, each of the two three-carbon sugar phosphates is converted to pyruvate. In the process, an energyrich hydrogen is harvested as NADH, and two ATP molecules are formed. glycolysis - steps 1. glucose (6 carbon-sugar) split into two, 3carbon sugars 2. sugars are oxidized and rearranged to form 2 molecules of pyruvate. 3. Each step catalyzed by specific enzyme 4. steps divided into 2 phases: an energy investment phase and an energy payoff phase. *Most of the energy contained in glucose is still stored in pyruvate, which goes into the Krebs Cycle Glycolysis yields 2 ATP and 2 pyruvates, 2 NADH net yield of glycoloysis 2ATP, 2NADH, 2 pyruvates Can it end here? Copyright © The McGraw-Hill Companies, Inc. Permission equired for reproduction or display. With oxygen Pyruvate H20 NAD+ O2 NADH Acetyl-CoA Without oxygen CO2 NADH NADH NAD+ Lactate Krebs cycle yeast in absence of oxygen (bread and wine) dump electrons from NADH onto acetaldehyde (converted from pyruvic acid by spewing off CO2)) reducing it to ethanol, and regenerating NAD+. Acetaldehyde NAD+ Ethanol • alcohol fermentationpyruvate converted to ethanol in 2 steps. • lactic acid fermentation in animals in absence of oxygen (muscle fatigue), pyruvate accepts electrons from NADH and regenerates NAD+, but is converted into lactic acid (muscle burn) • Muscle cells switch from AR to fermentation to generate ATP when O2 is scarce. • waste product, lactate -muscle fatigue, but ultimately converted back to pyruvate in the liver • used to make cheese and yogurt 4 stages of cellular respiration 1.Glycolysis 2.Pryuvate Oxidation 3.Krebs cycle 4.Electron transport chain *Pryuvate is “Fork in the road” pyruvate must be converted to Acetyl CoA Bridge between glycolysis and Krebs Cycle pyruvate enters mitochondria using transport protein in mitochondrial membrane, converted to Acetyl CoA (cofactor) - also releases NADH • Transition between Glycolysis and Krebs Cycle –In the presence of oxygen, each of the two pyruvic acids travels into the mitochondria. – Combine with coenzyme A to make acetyl CoA, one NADH, and CO2 –Next - Krebs cycle inner compartment of mitochondria Mitochondria • outer and inner phospholipid bilayer membrane • outer is smooth, inner membrane is folded crista (s) cristae(p) -matrix –SOLUTION - high concentration of enzymes REMEMBER mitochondrion? For LAST stage -enzyme ATP synthase embedded in inner membrane channel through which protons cross membrane Protons move down concentration gradient • ATP synthesis - rotary motor driven by a gradient of protons 4 stages of cellular respiration 1.Glycolysis 2.Pryuvate Oxidation 3.Krebs cycle 4.Electron transport chain *Pryuvate is “Fork in the road” 4 stages of cellular respiration 3rd step - Krebs Cycle *occurs in mitochondrial matrix *gives off 2 CO2/turn (each) *Yields 1 ATP, 3 NADH, & 1 FADH2 (each) glycolysis mitochondrion pyruvic acid cytosol NAD+ coenzyme A NADH to electron transport chain CoA CO2 inner compartment acetyl coenzyme A Krebs cycle SUMMARY OF THE KREBS CYCLE 6 NADH GLYCOLYSIS 2 FADH2 CoA Krebs cycle acetyl coenzyme A CO2 2 ATP electron transport chain oxaloacetic acid NADH 1. citric acid NAD+ NAD+ 6. CO2 α-ketoglutaric acid malic acid FADH2 2. NADH 3. FAD+ 5. ADP NAD+ note 1st product citric acid cycle note CO2 CO2 NADH 4. α-ketoglutaric acid derivative succinic acid ATP Krebs Cycle *8 reactions, 8 enzymes in the matrix *3 NADHs made for every Acetyl CoA molecule *1FADH2 for every Acetyl CoA *1ATP for every Acetyl CoA •cycle (aka citric acid cycle) • Importance of Krebs Cycle – Acetyl CoA broken down into CO2 – Only 1 ATP made for each acetyl CoA that enters (total 2 ATP per glucose) – But, most electrons have been “captured” onto 6 NADH and 2 FADH2 (per glucose) for last stage (electron transport chain) 4 stages of cellular respiration 1.Glycolysis 2.Pryuvate Oxidation 3.Krebs cycle 4.Electron transport chain *Pryuvate is “Fork in the road” 4 stages of cellular respiration finally - Payoff Electron transport chain *in inner mitochondria membrane *yields CO2 and water *AND Yields about 38 ATP!! Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intermembrane + H + space H+ H+ H + + H H+ H H+ Rotor Rod Catalytic head ADP + Pi ATP Mitochondrial matrix H+ chemiosmosis • Coupling (linking) • A) the movement of protons (Hydrogen minus its electron) • across a membrane (mitochondria) • B) to the synthesis of ATP inner membrane outer membrane H+ + H H+ H+ + H electron transport chain Krebs cycle + H H+ H+ + H eO2 outer compartment H2O inner compartment Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intermembrane space H+ H+ H+ Inner H+ mitochondrial membrane H+ ADP + Pi NAD+ NADH ATP Proton pump Mitochondrial matrix H+ ATP synthase • Electron Transport Chain • NADH and FADH2 drop off electrons onto molecules in inner membrane. – Movement of electrons powers the movement of H+ ions against concentration gradient. – pumps H+ from matrix into intermembrane space. – now H+ move down gradient back into matrix – energy is used to transfer phosphate onto ADP to make ATP. – Greatest amount made in this stage (28- 30 ATP /glucose) – end of the chain O2 + 2 electrons + 2 H + = H 2O – why we must breathe Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intermembrane space H+ H+ H+ Inner H+ mitochondrial membrane H+ ADP + Pi NAD+ NADH ATP Proton pump H+ ATP synthase Mitochondrial matrix Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pyruvate from cytoplasm Inner + mitochondrial H membrane H+ Intermembrane space Q NADH e1. Electrons are harvested and carried to the Acetyl-CoA transport system. NADH eKrebs cycle FADH2 CO2 2 ATP Mitochondrial matrix 2. Electrons provide energy to pump protons across the membrane. H2O e 3. Oxygen joins 1 O with protons to 2 +2 form water. 2H+ H+ 32 ATP 4. Protons diffuse back in down their concentration gradient, driving the synthesis of ATP. Electron transport C system H+ e- O2 H+ ATP synthase electrochemical gradient 1) H+ ions pumped out of matrix during the ETC 2) H+ flows through ATP synthase 3) shape change allows ADP to be phosphorylated how do mitochondria use energy released? Chemiosmosis - coupling energy released in the ETC to synthesis of ATP ATP production ATP generation in ETC oxidative phosphorylation occurs as result of redox reactions REMEMBER? • transfer of phosphate group from ATP phosphorylation Substrate level phosphorylation transfer of phosphate group from ATP phosphorylation Substrate level phosphorylation uses enzymes oxidative phosphorylation Uses proton gradient to produce ATP GLYCOLYSIS ELECTRON TRANSPORT CHAIN 32 ATP inner membrane inner compartment H2 O O2 outer compartment H+ H+ outer compartment H+ H+ inner membrane mitochondrion KREBS CYCLE H+ H+ H+ H+ ATP SYNTHESIS H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ NADH H+ NAD+ 2 H+ + 1/2 O2 inner compartment ATP synthesis ADP + P H2 O ATP ELECTRON TRANSPORT CHAIN Duration of maximal exercise Minutes Seconds 10 30 60 2 4 10 30 60 120 Percent 90 anaerobic 80 70 50 35 15 5 2 1 Percent aerobic 20 30 50 65 85 95 98 99 10 ATP Generation during Exercise –What is greatest source of energy—aerobic or anaerobic –HOW fast would we go without mitrochondria? Feedback mechanisms control cellular respiration • Metabolic control of cellular respiration - supply and demand – If ATP levels drop, catabolism speeds up to produce more ATP – based on regulating activity of enzymes at strategic points in the catabolic pathway example: third step of glycolysis • catalyzed by phosphofructokinase (PKF) • Allosteric regulation of phosphofructokinase sets the pace of respiration Allosteric? remote site Without oxygen • Fermentation • ALSO carbon dioxide (Archaea) • ALSO sulfur (bacteria) • Carbohydrates, fats, and proteins all catabolized through the same pathways!!!! a gram of fat will generate twice as much ATP as a gram of carbohydrate How did we get here? Evolution • • • • • • Break down carbon (store in ATP) Glycolysis (series 2 billion years old) Photosynthesis - no oxygen Photosynthesis - forming oxygen Nitrogen “fixation” before oxygen Aerobic respiration which is faster enzyme activity lab Or NEXT TIME cellular respiration lab? •Recall cellular respiration •C6H12O6 + 6O2 -----> 6CO2 + 6H2O + Energy •compare to photosynthesis : 6CO2 + 6H2O + light energy -----> C6H12O6 + 6O2