ourse o: BG00" redits:.00 " General Biology " " 6. ellular Respiration: arvesting hemical Energy verview: Life is Work Living cells require transfusions of energy from outside sources to perform their many tasks The giant panda obtains energy for its cells by eating plants rof. Dr. Klaus eese Energy flows into an ecosystem as sunlight and leaves it as heat Light energy atabolic pathways yield energy by oxidizing organic fuels atabolic athways and roduction of ESYSTEM hotosynthesis in chloroplasts rganic molecules ellular respiration in mitochondria powers most cellular work eat energy The breakdown of organic molecules is exergonic ne catabolic process, fermentation is a partial degradation of sugars that occurs without oxygen ellular respiration is the most prevalent and efficient catabolic pathway consumes oxygen and organic molecules such as glucose yields To keep working ells must regenerate Redox Reactions: xidation and Reduction atabolic pathways yield energy due to the transfer of electrons The rinciple of Redx Redx reactions Transfer electrons from one reactant to another by oxidation and reduction Examples of Redx reactions becomes oxidized (loses electron) a l a l becomes reduced (gains electron) In oxidation a substance loses electrons, or is oxidized In reduction a substance gains electrons, or is reduced 1
Some Redx reactions do not completely exchange electrons change the degree of electron sharing in covalent bonds xidation of rganic Fuel Molecules During ellular Respiration During cellular respiration is oxidized and oxygen is reduced Reactants becomes oxidized roducts 6 1 6 6 becomes oxidized 6 6 Energy 4 Energy becomes reduced becomes reduced Stepwise Energy arvest via AD and the Electron Transport hain ellular respiration Methane (reducing agent) xygen (oxidizing agent) arbon dioxide Water xidizes glucose in a series of steps Electrons from organic compounds are usually first transferred to AD, a coenzyme AD icotinamide (oxidized form) AD, the reduced form of AD Dehydrogenase [] Reduction of AD (from food) xidation of AD e e AD icotinamide (reduced form) passes the electrons to the electron transport chain If electron transfer is not stepwise a large release of energy occurs as in the reaction of hydrogen and oxygen to form water Free energy, G 1 / Explosive release of heat and light energy (a) Uncontrolled reaction oxyhydrogen (denotating/explosive) gas The electron transport chain passes electrons in a series of steps instead of in one explosive reaction uses the energy from the electron transfer to form Free energy, G 1 / (from food via AD) ontrolled e release of energy for synthesis of Electron transport chain e 1 / (b) ellular respiration The Stages of ellular Respiration: A review Respiration is a cumulative function of three metabolic stages The citric xidative Breaks down glucose into two molecules of pyruvate The citric ompletes the breakdown of glucose xidative is driven by the electron transport chain generates
An overview of cellular respiration the principle three metabolic stages Electrons carried via AD Electrons carried via AD and FAD Both glycolysis and the citric can generate by substrate-level Enzyme Enzyme ytosol Mitochondrion xidative : electron transport and chemiosmosis Substrate roduct Substrate-level Substrate-level xidative harvests energy by oxidizing glucose to pyruvate means splitting of sugar consists of two major phases Energy investment phase Energy payoff phase xidative breaks down glucose into pyruvate Energy investment phase occurs in the cytoplasm of the cell Energy payoff phase used 4 4 4 formed AD 4 e - 4 AD 4 formed used AD 4 e 4 AD A closer look at the energy investment phase 1 xidative A closer look at the energy payoff phase AD AD 6 Triose phosphate dehydrogenase i -6-phosphate exokinase 1, -Bisphosphoglycerate 7 hosphoglycerokinase Fructose-6-phosphate hosphoglucoisomerase -hosphoglycerate 8 hosphoglyceromutase hosphofructokinase -hosphoglycerate Fructose- 1, 6-bisphosphate Aldolase 4 9 Enolase hosphoenolpyruvate 10 kinase Dihydroxyacetone phosphate 5 Isomerase Glyceraldehyde- -phosphate
The citric completes the energy-yielding oxidation of organic molecules The citric takes place in the matrix of the mitochondrion Before the citric can begin must first be converted to acetyl oa, which links the to glycolysis YTSL Transport protein 1 AD AD oenzyme A MITDRI S oa Acetyle oa An overview of the citric (Krebs ycle) (from glycolysis, molecules per glucose) FAD FAD AD Acetyle oa oa oa oa i xidative AD AD xidative S oa During oxidative, chemiosmosis couples electron transport to synthesis A closer look at the citric Acetyl oa oa S AD 1 AD 8 xaloacetate Malate itrate Isocitrate Figure 9.1 7 AD AD Fumarate oa S α-ketoglutarate 4 6 oa S FAD 5 AD FAD Succinate oa i S AD GT GD Succinyl oa AD and FAD donate electrons to the electron transport chain, which powers synthesis via oxidative The athway of Electron Transport In the electron transport chain electrons from AD and FAD lose energy in several steps At the end of the chain electrons are passed to oxygen, forming water Free energy (G) relative to (kcl/mol) 50 40 0 0 10 0 AD FAD I Multiprotein FM FAD complexes Fe S Fe S II III yt b Fe S yt c 1 IV yt c yt a yt a 1 hemiosmosis and the electron transport chain Intermembrane space Inner mitochondrial membrane Mitochondrial matrix xidative. electron transport and chemiosmosis rotein complex of electron carners AD I II AD Q III yt c IV FAD FAD 1 / (arrying electrons from, food) Electron transport chain Electron transport and pumping of protons ( ), which create an gradient across the membrane xidative i Inner Mitochondrial membrane hemiosmosis synthesis powered by the flow f back across the membrane An Accounting of roduction by ellular Respiration synthase During respiration, most energy flows in this sequence glucose to AD to electron transport chain to proton-motive force to At certain steps along the electron transport chain Electron transfer causes protein complexes to pump from the mitochondrial matrix to the intermembrane space The resulting gradient stores energy drives chemiosmosis in synthase is referred to as a proton-motive force (pmf) hemiosmosis Is an energy-coupling mechanism that uses energy in the form of a gradient across a membrane to drive cellular work 4
hemiosmosis: The Energy-oupling Mechanism synthase is the enzyme that actually makes Aerobic oxidation of pyruvate and fatty s in mitochondria The proton motive force (pmf) ITERMEMBRAE SAE A rotor within the membrane spins clockwise when flows past it down the gradient. A stator anchored in the membrane holds the knob stationary. A rod (for stalk ) extending into the knob also spins, activating catalytic sites in the knob. i MITDRIAL MATRIX Three catalytic sites in the stationary knob join inorganic hosphate to to make. The outer membrane is freely permeable to all metabolites, but specific transport proteins (colored ovals) in the inner membrane are required to import pyruvate (yellow), (green), and i (purple) into the matrix and to export (green). AD generated in the cytosol is not transported directly to the matrix because the inner membrane is impermeable to AD and AD; instead, a shuttle system (red) transports electrons from cytosolic AD to AD in the matrix. diffuses into the matrix and diffuses out. Stage-1: fatty acyl groups are transferred from fatty acyl oa and transported across the inner membrane via a special carrier (blue oval) and then reattached to oa on the matrix side. is converted to acetyl oa with the formation of AD, and fatty s (attached to oa) are also converted to acetyl oa with formation of AD and FAD. xidation of acetyl oa in the citric generates AD and FAD. Stage-: electrons from these reduced coenzymes are transferred via electron transport complexes (blue boxes) to concomitant with transport of ions from the matrix to the intramembrane space, generating the proton-motive force. Electrons from AD flow directly from complex I to complex III, bypassing complex II. Stage : synthase, the F 0 F 1 complex (orange), harnesses the proton-motive force to synthesize. Blue arrows indicate electron flow; red arrows transmembrane movement of protons; and green arrows indicate transport of metabolites. The phosphate and / transport system in the inner mitochondrial membrane There are three main processes in this metabolic enterprise YTSL Electron shuttles span membrane AD or MITDRI FAD AD AD 6 AD FAD Acetyl oa xidative : electron transport and chemiosmosis about or 4 by substrate-level by substrate-level by oxidative, depending on which shuttle transports electrons from AD in cytosol Maximum per glucose: About 6 or 8 The coordinated action of two antiporters (purple and green) results in the uptake of one - and one 4 - in exchange for one during e - transport. The outer membrane is not shown here because it is permeable to molecules smaller than 5kDa. About 40% of the energy in a glucose molecule is transferred to during cellular respiration, making approximately 8 Fermentation enables some cells to produce without the use of oxygen ellular respiration relies on oxygen to produce In the absence of oxygen cells can still produce through fermentation can produce with or without oxygen, in aerobic or anaerobic conditions couples with fermentation to produce Types of Fermentation ( without the use of oxygen) Fermentation consists of - glycolysis plus reactions that regenerate AD, which can be reused by glyocolysis In alcohol fermentation pyruvate is converted to ethanol in two steps, one of which releases During lactic fermentation pyruvate is reduced directly to AD to form lactate as a waste product Ethanol 1 (a) Alcohol fermentation Lactate AD AD 1 AD AD (b) Lactic fermentation Acetaldehyde 5
Fermentation and ellular Respiration ompared Both fermentation and cellular respiration use glycolysis to oxidize glucose and other organic fuels to pyruvate Fermentation and cellular respiration differ in their final electron acceptor ellular respiration produces more pyruvate is a key juncture in catabolism YTSL o present Fermentation Ethanol or lactate present ellular respiration Acetyl oa MITDRI and the citric connect to many other metabolic pathways The Versatility of atabolism atabolic pathways Funnel electrons from many kinds of organic molecules into cellular respiration The catabolism of various molecules from food roteins Amino s arbohydrates Sugars Glycerol Fatty s Glyceraldehyde-- Acetyl oa xidative Fats Biosynthesis (Anabolic athways) The body uses small molecules to build other substances These small molecules may come directly from food or through glycolysis or the citric Inhibits Fructose-6-phosphate hosphofructokinase Fructose-1,6-bisphosphate AM Stimulates Inhibits Regulation of ellular Respiration via Feedback Mechanisms Acetyl oa itrate ellular respiration is controlled by allosteric enzymes at key points in glycolysis and the citric xidative 6