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 •C6H12O6 + 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 extracellular Enzyme muscle cells Calcium ions –Calcium ions move to enzyme ATP binding Ca++ site Ca++ ATP –ATP splits -ADP and P phosphate ADP Ca++ P Cytosol –energy transfers phosphate intracellualr onto protein Ca++ P – –shape change drives calcium across membrane P biochemical pathways •ATP: Important Energy Storage Molecule energy stored as phosphate bond in ATP 3rd phosphate group energy released added to ADP when phosphate bond broken using energy from food p p p ATP energy energy IN OUT energy hill p p p p p p P + ADP 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) C4H10N3O5P (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 Sepsis Altitude sickness Blood loss 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+ NADH NAD+ empty loaded empty + + H proton NAD + H oxidized - + - + NAD NAD H - - - + - 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 NADH Pyruvate CO Intermembrane oxidation 2 space Acetyl- CoA Mitochondrial matrix NADH CO2 Krebs cycle ATP FADH2 H2O ATP NAD+ and FAD - e Electron transport chain Inner mitochondrial membrane Mitochondrion •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 2 3 6-carbon glucose (Starting material) 2 ATP P P P P 6-carbon sugar diphosphate 6-carbon sugar diphosphate SOME ENERGY OUT! P P P P ENERGY IN!!!!!! 3-carbon sugar 3-carbon sugar 3-carbon sugar 3-carbon sugar phosphate phosphate phosphate phosphate NADH NADH 2 ATP 2 ATP 3-carbon 3-carbon pyruvate pyruvate Priming reactions. Priming Cleavage reactions. Then, the Energy-harvesting reactions. reactions. Glycolysis begins with six-carbon molecule with two Finally, in a series of reactions, each the addition of energy. Two high- phosphates is split in two, forming of the two three-carbon sugar energy phosphates from two two three-carbon sugar phosphates is converted to molecules of ATP are added to the pyruvate. In the process, an energy- six-carbon molecule glucose, phosphates. rich hydrogen is harvested as producing a six-carbon molecule NADH, and two ATP molecules are with two phosphates. formed. glycolysis - steps 1. glucose (6 carbon-sugar) split into two, 3- carbon 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 Without oxygen Pyruvate + H20 NAD CO2 NADH O2 NADH Acetaldehyde NADH Acetyl-CoA NAD+ + Lactate NAD Krebs cycle Ethanol • alcohol fermentation- pyruvate converted yeast to ethanol in 2 steps. 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+. • 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