General Biology. Overview: Life is Work. 6. Cellular Respiration: Harvesting Chemical Energy. Energy

Transcription

1 ourse No: BNG003 redits: 3.00 General Biology 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 6. ellular Respiration: arvesting hemical Energy Prof. 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 Pathways and Production of ESYSTEM The breakdown of organic molecules is exergonic ne catabolic process, fermentation + Photosynthesis in chloroplasts ellular respiration in mitochondria rganic molecules + is a partial degradation of sugars that occurs without oxygen ellular respiration is the most prevalent and efficient catabolic pathway eat energy powers most cellular work consumes oxygen and organic molecules such as glucose yields

2 To keep working ells must regenerate Redox Reactions: xidation and Reduction atabolic pathways yield energy due to the transfer of electrons The Principle of Redx Redx reactions Examples of Redx reactions becomes oxidized (loses electron) Na + l Na + + l becomes reduced (gains electron) Transfer electrons from one reactant to another by oxidation and reduction In oxidation a substance loses electrons, or is oxidized In reduction a substance gains electrons, or is reduced 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 Products becomes oxidized Energy Energy + becomes reduced becomes reduced Stepwise Energy arvest via and the Electron Transport hain ellular respiration Methane (reducing agent) xygen (oxidizing agent) arbon dioxide Water xidizes glucose in a series of steps

3 Electrons from organic compounds are usually first transferred to, a coenzyme N + P P N N N Nicotinamide (oxidized form) N N N + [] (from food) e + + e + + NAD Dehydrogenase Reduction of xidation of NAD N N + Nicotinamide (reduced form) + 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 + / Explosive release of heat and light energy Uncontrolled reaction NAD, the reduced form of passes the electrons to the electron transport chain oxyhydrogen (detonating/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 + / (from food via NAD) ontrolled release of energy for synthesis of + + e e + ellular respiration / The Stages of ellular Respiration: A Preview 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 3

4 An overview of cellular respiration the principle three metabolic stages Electrons carried via NAD Electrons carried via NAD and FAD Both glycolysis and the citric can generate by substrate-level Enzyme Enzyme xidative : electron transport and chemiosmosis ytosol Mitochondrion Substrate P + Product Substrate-level Substrate-level xidative harvests energy by oxidizing glucose to pyruvate consists of two major phases Energy investment phase Energy payoff phase xidative means splitting of sugar Energy investment phase breaks down glucose into pyruvate occurs in the cytoplasm of the cell + P Energy payoff phase used P 4 formed + 4 e formed used e NAD 4

5 A closer look at the energy investment phase P -6-phosphate exokinase xidative A closer look at the energy payoff phase 6 Triose phosphate dehydrogenase NAD P i + + P P, 3-Bisphosphoglycerate 7 Phosphoglycerokinase P Fructose-6-phosphate Phosphoglucoisomerase P 3-Phosphoglycerate 8 Phosphoglyceromutase 3 Phosphofructokinase P -Phosphoglycerate P P Fructose-, 6-bisphosphate Aldolase 4 9 Enolase P Phosphoenolpyruvate 0 kinase P Dihydroxyacetone phosphate 5 Isomerase P Glyceraldehyde- 3-phosphate 3 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 3 Transport protein + oenzyme A MITNDRIN 3 S 3 oa Acetyle oa An overview of the citric (Krebs ycle) (from glycolysis, molecules per glucose) FAD FAD NAD Acetyle oa oa oa oa + P i xidative 3 NAD

6 xidative S oa During oxidative, chemiosmosis couples electron transport to synthesis A closer look at the citric 3 Acetyl oa oa S NAD Malate 7 FAD Fumarate xaloacetate Figure 9. FAD Succinate P i GTP GDP itrate oa S 6 4 oa S 5 S oa Succinyl + + oa Isocitrate 3 NAD + + a-ketoglutarate NAD NAD and FAD donate electrons to the electron transport chain, which powers synthesis via oxidative The Pathway of Electron Transport In the electron transport chain electrons from NAD 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) NAD I FMN Fe S FAD FAD Fe S II III yt b Fe S yt c Multiprotein complexes yt c yt a + + IV yt a3 hemiosmosis and the electron transport chain Intermembrane space Inner mitochondrial membrane Mitochondrial matrix xidative. electron transport and chemiosmosis Protein complex of electron carners I + + II Q III yt c FAD FAD + + / (arrying electrons from food) Electron transport chain Electron transport and pumping of protons ( + ), which create an + gradient across the membrane IV + xidative + P i + + Inner Mitochondrial membrane hemiosmosis synthesis powered by the flow f + back across the membrane An Accounting of Production by ellular Respiration synthase During respiration, most energy flows in this sequence glucose to NAD 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 6

7 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) + INTERMEMBRANE SPAE 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. + P i MITNDRIAL MATRIX Three catalytic sites in the stationary knob join inorganic Phosphate 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 Pi (purple) into the matrix and to export (green). NAD generated in the cytosol is not transported directly to the matrix because the inner membrane is impermeable to and NAD; instead, a shuttle system (red) transports electrons from cytosolic NAD to in the matrix. diffuses into the matrix and diffuses out. Stage-: 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 NAD, and fatty s (attached to oa) are also converted to acetyl oa with formation of NAD and FAD. xidation of acetyl oa in the citric generates NAD 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 NAD flow directly from complex I to complex III, bypassing complex II. Stage 3: synthase, the F0F 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 NAD or MITNDRIN FAD NAD NAD 6 NAD FAD Acetyl oa xidative : electron transport and chemiosmosis about 3 or 34 by substrate-level by substrate-level by oxidative, depending on which shuttle transports electrons from NAD in cytosol Maximum per glucose: About 36 or 38 The coordinated action of two antiporters (purple and green) results in the uptake of one 3- and one P 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 38 7

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, 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 NAD to form lactate as a waste product + P NAD 3 Ethanol (a) Alcohol fermentation + P NAD 3 Lactate (b) Lactic fermentation 3 3 Acetaldehyde 3 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 YTSL No present Fermentation present ellular respiration 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 N 3 Proteins Amino s arbohydrates Sugars Glycerol Fatty s Glyceraldehyde-3- P Fats differ in their final electron acceptor ellular respiration produces more Ethanol or lactate Acetyl oa MITNDRIN The catabolism of various molecules from food Acetyl oa pyruvate is a key juncture in catabolism xidative 8

9 Biosynthesis (Anabolic Pathways) 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 Phosphofructokinase Fructose-,6-bisphosphate AMP 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 9