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Transcript
Respiration • Cells - energy to do work - stored as organic molecules - broken down to get energy. • 2 ways - 1 in absence of oxygen (fermentation). • Other aerobic (presence of oxygen) - respiration. http://www.jracademy.com/~vinjama/2003pics/fermentation%5B1%5D.jpg • Formula for respiration: C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP + heat) • Glucose traditionally used - any organic molecule can be starting material. http://tidepool.st.usm.edu/pix/resp.gif • ATP (adenosine triphosphate) molecule used in energy. • When has phosphate group - like loaded spring; when loses phosphate group, energy released. • Energy comes from conversion of ATP to ADP and inorganic phosphate (Pi). • Animal cells can regenerate ATP back from Pi and ADP by breaking down organic molecules. http://www.med8th.com/nobel/winners/1992/1992-phosphorylation.jpg • Movement of end phosphorus group from one molecule to another phosphorylation. • Temporarily changes shape of molecule; changes back to original shape when phosphate leaves. • Redox reaction - electrons transferred from 1 reactant to another. • Loss of electrons - oxidation. • Addition of electrons - reduction. • Electron donor - reducing agent; electron recipient - oxidizing agent. http://www.emc.maricopa.edu/faculty/farabee/BIOBK/redox.gif • Respiration is a redox reaction. • Glucose oxidized, oxygen reduced, electrons lose potential energy. http://bioweb.wku.edu/courses/BIOL115/Wyatt/Metabolism/Respiration.gif • At key steps, hydrogen atoms stripped from glucose, passed 1st to coenzyme (i.e. NAD+) • Turns NAD+ into NADH. • NADH shuttles electrons from food to “top” of chain. • At “bottom,” oxygen captures electrons and H+ to form water. http://kvhs.nbed.nb.ca/gallant/biology/etc.jpg • 3 stages in respiration: glycolysis, Krebs cycle, electron transport chain and oxidative phosphorylation. • Glycolysis – cytoplasm; Krebs cycle - mitochondrial matrix. • Glycolysis and Krebs cycle electrons passed from substrates to NAD+, forming NADH. • NADH passes electrons to electron transport chain (ETC). • In ETC electrons move from molecule to molecule until they combine with O2 and H+ ions to form water. http://www.biology.lsu.edu/introbio/spring/Spring%202005/1001/SMP/Overall%20summary%20of%20Glycolysis%20and%20the%20Krebs%20Cycle.jpg • During ETC energy carried by electrons stored in mitochondrion in form used to synthesize ATP via oxidative phosphorylation. • ATP also generated in glycolysis and Krebs cycle by substrate-level phosphorylation. • Enzyme transfers phosphate group from organic molecule (substrate) to ADP, forming ATP. * • 38 ATP produced per mole of glucose - broken down to CO2 and H2O by respiration. • 34 ATP made through oxidative phosphorylation , 4 ATP from substrate-level phosphorylation giving 38 total ATP molecules. http://www.nismat.org/physcor/atp.gif • During glycolysis, glucose, 6-C sugar split into (2) 3-C sugars. • Net yield from glycolysis 2 ATP and 2 NADH per glucose. • Glycolysis occurs whether O2 present or not. • O2 present, pyruvate moves into Krebs cycle. • More than ¾ of original energy in glucose still present in 2 molecules of pyruvate. • Pyruvate first modified into acetyl CoA (actually enters Krebs cycle) • Each turn of Krebs cycle produces 1 ATP, 3 NADH, 1 FADH2 (electron carrier) for every molecule of acetyl CoA. • Most ATP generated during respiration comes from energy in electrons carried by NADH (and FADH2). • Energy in these electrons used in ETC to make ATP. http://www.stanford.edu/group/hopes/treatmts/ebuffer/f_j03nadhrole.gif • As electrons move down ETC they pass energy. • Transported by either NADH or FADH2.. • Purpose of ETC - break up energy into smaller amounts - released in smaller amounts. • ATP synthase makes ATP from ADP and Pi. • ATP synthesis generated through proton gradient produced by movement of electrons along ETC. • Gradient made when there is higher concentration in one area. • Several chain molecules use flow of electrons to pump H+ from matrix to intermembrane space. • Concentration of H+ - proton-motive force. • ATP synthase molecules only place that allow H+ to diffuse back to matrix of mitochondria. • Coupling ETC with ATP synthesis called chemiosmosis - helps generate ATP. http://fig.cox.miami.edu/~cmallery/150/makeatp/chemiosmosis.jpg • Glycolysis produces 2 ATP whether or not O2 present. • O2 present, additional ATP generated when NADH delivers electrons to ETC. • If no O2 present - process fermentation. http://www.mr-damon.com/experiments/2sp/projects/images/fermentation.jpg • If NAD+ present, electrons accepted whether or not O2 present. • During fermentation, ATP generated by glycolysis; NAD+ recycled by transferring electrons from NADH to pyruvate. • Aerobic conditions, NADH transfers electrons to ETC, recycling NAD+. http://www.botany.unibe.ch/deve/images/ethferm1.gif • Alcohol fermentation, pyruvate converted to ethanol in 2 steps. • 1st, pyruvate converted to 2-C compound (acetaldehyde) by removal of CO2. • 2nd, acetaldehyde reduced by NADH to ethanol (used in brewery). • Lactic acid fermentation, pyruvate reduced directly by NADH to form lactate (form of lactic acid). • Muscle cells switch from aerobic respiration to lactic acid fermentation to generate ATP when O2 is scarce. • Waste – lactate; buildup causes muscle soreness. • Aerobic respiration, 38 ATP generated (2 produced through anaerobic respiration for 1 molecule of glucose). • Some organisms (facultative anaerobes), including yeast, bacteria, survive using either fermentation or respiration. • Glycolysis can occur with many organic molecules. • If not carbohydrate - must be broken down 1st. • Fats give 2x as much ATP as carbohydrates. http://www.teachnet.ie/gmcweeney/images/fats.JPG • Respiration monitored through supply and demand. • Glycolysis - phosphofructokinase (enzyme) speeds up or slows down glycolysis. • If enzyme active - because ATP levels low - respiration speeds up. • http://www.teachersdomain.org/resources/t dc02/sci/life/cell/mitochondria/index.html