Presentation on theme: "Catabolism : Energy Release and Conservation"— Presentation transcript:
1 Catabolism : Energy Release and Conservation Chapter 10Catabolism : Energy Release and ConservationCHAPTER GLOSSARYAerobic respirationAnaerobic respirationAnoxygenic photosynthesisATP synthaseBacteriochlorophyllBacteriorhodopsin紫紅質Chemiosmotic hypothesisChemolithotroph營Chlorophyll葉綠素Cyclic photophosphorylationDark reactionsEmbden-Meyerhof pathwayEntner-Doudoroff pathwayFermentationGlycolysisLight reactionsNoncyclic photophosphorylationOxidative phosphorylationOxygenic photosynthesisPentose phosphate pathwayPhotophosphorylationPhotosynthesisProton motive force (PMF)Substrate-level phosphorylationTricarboxylic acid (TCA) cycle
2 Chemoorganotrophic fueling processes also called chemoheterotrophsprocessesaerobic respirationanaerobic respirationfermentation
3 Chemoorganic fueling processes-respiration most respiration involves use of an electron transport chainas electrons pass through the electron transport chain to the final electron acceptor, a proton motive force (PMF) is generated and used to synthesize ATPaerobic respirationfinal electron acceptor is oxygenanaerobic respirationfinal electron acceptor is different exogenous acceptor such asNO3-, SO42-, CO2, Fe3+, or SeO42-organic acceptors may also be usedATP made primarily by oxidative phosphorylation
4 Chemoorganic fueling processes - fermentation uses an endogenous electron acceptorusually an intermediate of the pathway used to oxidize the organic energy source e.g., pyruvatedoes not involve the use of an electron transport chain nor the generation of a proton motive forceATP synthesized only by substrate-level phosphorylation
5 Energy Sourcesmany different energy sources are funneled into common degradative pathwaysmost pathways generate glucose or intermediates of the pathways used in glucose metabolismfew pathways greatly increase metabolic efficiency
6 Catabolic Pathways Amphibolic Pathways enzyme catalyzed reactions whereby the product of one reaction serves as the substrate for the nextpathways also provide materials for biosynthesisamphibolic有二義的pathwaysAmphibolic Pathwaysfunction both as catabolic and anabolic pathwaysimportant onesEmbden-Meyerhof pathwaypentose phosphate pathwaytricarboxylic acid (TCA) cycle
7 Aerobic Respirationprocess that can completely catabolize an organic energy source to CO2 usingglycolytic pathways (glycolysis)TCA cycleelectron transport chain with oxygen as the final electron acceptorproduces ATP, and high energy electron carriers
8 The Breakdown of Glucose to Pyruvate Three common routesEmbden-Meyerhof pathwayEntner-Doudoroff pathwaypentose phosphate pathwayThe Embden-Meyerhof Pathwayoccurs in cytoplasmic matrix of most microorganisms, plants, and animalsthe most common pathway for glucose degradation to pyruvate in stage two of aerobic respirationfunction in presence or absence of O2two phasesglucose + 2ADP + 2Pi + 2NAD+↓2 pyruvate + 2ATP + 2NADH + 2H+
9 The Embden-Meyerhof Pathway addition of phosphates“primes the pump”oxidation step – generates NADHhigh-energy molecules – used to synthesize ATP by substrate-level phosphorylation
10 The Entner-Doudoroff Pathway used by soil bacteria and a few gram-negative bacteriareplaces the first phase of the Embden-Meyerhof pathwayyield per glucose molecule:1 ATP1 NADPH1 NADHreactions ofEntner-Doudoroff Pathwayreactions ofEmbden-Meyerhof Pathway
11 The Pentose Phosphate Pathway also called hexose monophosphate pathwaycan operate at same time as glycolytic pathway or Entner-Doudoroff pathwaycan operate aerobically or anaerobicallyan amphibolic pathwaySummary of pentose phosphate pathwayglucose-6-P + 12NADP+ + 7H2O6CO2 + 12NADPH + 12H+ Pi
12 The Pentose Phosphate Pathway Produce NADPH, which is needed forbiosynthesissugartrans-formationreactionsOxidation stepsproducesugarsneededforbiosynthesissugars canalso befurtherdegraded
13 The Tricarboxylic Acid Cycle also called citric acid cycle and Kreb’s cyclecommon in aerobic bacteria, free-living protozoa, most algae, and fungimajor role is as a source of carbon skeletons for use in biosynthesisfor each acetyl-CoA molecule oxidized, TCA cycle generates:2 molecules of CO23 molecules of NADHone FADH2one GTP
14 Electron Transport and Oxidative Phosphorylation only 4 ATP molecules synthesized directly from oxidation of glucose to CO2most ATP made when NADH and FADH2 (formed as glucose degraded) are oxidized in electron transport chain (ETC)Electron Transport Chainsthe mitochondrial electron transport chain (ETC) is composed of a series of electron carriers that operate together to transfer electrons from NADH and FADH2 to a terminal electron acceptor, O2electrons flow from carriers with more negative reduction potentials (E0) to carriers with more positive E0
15 The Electron Transport Chain each carrier is reduced and then reoxidizedcarriers are constantly recycledthe difference in reduction potentials electron carriers, NADH and O2 is large, resulting in release of great deal of energylarge difference in E0 of NADH and E0 of O2large amount ofenergy released
16 Mitochondrial ETCin eukaryotes the electron transport chain carriers are within the inner mitochondrial membrane and connected by coenzyme Q and cytochrome celectron transfer accompanied by proton movement across inner mitochondrial membraneProton release into the intermembrane space occurs when electrons are transferred from carriers (e.g., FMN and A) that carry both electrons and protons to components (e.g., FES proteins and Cyt) that transport only electrons.
17 Bacterial and Archaeal ETCs located in plasma membranesome resemble mitochondrial ETC, but many are differentdifferent electron carriersmay be branchedmay be shortermay have lower P/O ratioParacoccus denitrificansfacultative, soil bacteriumextremely versatile metabolicallyunder oxic conditions, uses aerobic respirationsimilar electron carriers and transport mechanism as mitochondriaprotons transported to periplasmic space rather than inner mitochondrial membranecan use one carbon molecules instead of glucose
18 Electron Transport Chain of E. coli Different array of cytochromes used than in mitochondrialbranched pathwayupper branch – stationary phase and low aerationlower branch – log phase and high aeration通風
19 Oxidative Phosphorylation Process by which ATP is synthesized as the result of electron transport driven by the oxidation of a chemical energy sourceChemiosmotic hypothesisthe most widely accepted hypothesis to explain oxidative phosphorylationelectron transport chain organized so protons move outward from the mitochondrial matrix as electrons are transported down the chainproton expulsion during electron transport results in the formation of a concentration gradient of protons and a charge gradientthe combined chemical and electrical potential difference make up the proton motive force (PMF)
21 PMF drives ATP synthesis diffusion of protons back across membrane (down gradient) drives formation of ATPATP synthaseenzyme that uses PMF down gradient to catalyze ATP synthesisfunctions like rotary engine with conformational changesImportance of PMF
22 ATP synthase structure and function The major structural features of ATP synthase deduced from X-ray crystallography and other studies. F1 is a spherical structure composed largely of alternating and subunits; the three active sites are on the subunits. The subunit extends upward through the center of the sphere and can rotate. The stalk ( and subunits) connects the sphere to F0, the membrane embedded complex that serves as a proton channel. F0 contains one a subunit, two b subunits, and 9-12 c subunits. The stator arm is composed of subunit a, two b subunits, and the subunit; it is embedded in the membrane and attached to F1. A ring of c subunits in F0 is connected to the stalk and may act as a rotor and move past the a subunit of the stator. As the c subunit ring turns, it rotates the shaft ( subunits).
23 ATP Yield During Aerobic Respiration maximum ATP yield can be calculatedincludes P/O ratios of NADH and FADH2ATP produced by substrate level phosphorylationthe theoretical maximum total yield of ATP during aerobic respiration is 38the actual number closer to 30 than 38
24 Theoretical vs. Actual Yield of ATP amount of ATP produced during aerobic respiration varies depending on growth conditions and nature of ETCunder anaerobic conditions, glycolysis only yields 2 ATP moleculesFactors Affecting ATP Yieldbacterial ETCs are shorter and have lower P/O ratiosATP production may vary with environmental conditionsPMF in bacteria and archaea is used for other purposes than ATP production (flagella rotation)precursor metabolite may be used for biosynthesis
25 Anaerobic Respiration uses electron carriers other than O2generally yields less energy because E0 of electron acceptor is less positive than E0 of O2
26 An Example… dissimilatory異化 nitrate reduction use of nitrate as terminal electron acceptorthe anaerobic reduction of nitrate makes it unavailable to cell for assimilation (同化, 吸收) or uptakedenitrificationreduction of nitrate to nitrogen gasin soil, causes loss of soil fertilityETC of Paracoccus denitrificans - anaerobic
27 Fermentation oxidation of NADH produced by glycolysis pyruvate or derivative used as endogenous electron acceptorsubstrate only partially oxidizedoxygen not neededoxidative phosphorylation does not occurATP formed by substrate-level phosphorylation
28 homolacticfermentersalcoholicfermentationheterolacticfermentersalcoholicbeverages,bread, etc.foodspoilageyogurt,sauerkraut德國泡菜,pickles泡菜, etc.
30 Catabolism of Other Carbohydrates many different carbohydrates can serve as energy sourcecarbohydrates can be supplied externally or internally (from internal reserves)monosaccharidesconverted to other sugars that enter glycolytic pathwaydisaccharides and polysaccharidescleaved by hydrolases or phosphorylases
31 (glucose)n + Pi (glucose)n-1 + glucose-1-P Reserve Polymersused as energy sources in absence of external nutrientse.g., glycogen and starchcleaved by phosphorylases(glucose)n + Pi (glucose)n-1 + glucose-1-Pglucose-1-P enters glycolytic pathwaye.g., Poly-b-hydroxybutyrate (PHB)the soil bacterium AzotobacterPHB acetyl-CoAacetyl-CoA enters TCA cycle
32 Lipid Catabolism triglycerides common energy sources hydrolyzed to glycerol and fatty acids by lipasesglycerol degraded via glycolytic pathwayfatty acids often oxidized via β-oxidation pathway
34 Protein and Amino Acid Catabolism proteasehydrolyzes protein to amino acidsdeaminationremoval of amino group from amino acidresulting organic acids converted to pyruvate, acetyl-CoA, or TCA cycle intermediatecan be oxidized via TCA cyclecan be used for biosynthesiscan occur through transaminationtransfer of amino group from one amino acid to α-keto acid
35 Chemolithotrophy carried out by chemolithotrophs由氧化無機物得到能源的自養有機體 electrons released from energy source which is an inorganic moleculetransferred to terminal electron acceptor (usually O2 ) by ETCATP synthesized by oxidative phosphorylation
36 Energy Sourcesbacterial and archaeal species have specific electron donor and acceptor preferencesmuch less energy is available from oxidation of inorganic molecules than glucose oxidation due to more positive redox potentials
37 Three Major Groups of Chemolithotrophs have ecological importanceseveral bacteria and archaea oxidize hydrogensulfur-oxidizing microbeshydrogen sulfide (H2S), sulfur (S0), thiosulfate (S2O32-)nitrifying bacteria oxidize ammonia to nitrate
38 Sulfur-oxidizing bacteria ATP can be synthesized by both oxidative phosphorylation and substrate-level phosphorylation
39 Nitrifying Bacteria Example requires 2 different generaoxidize ammonia to nitrate NH4+ NO2- NO3-Top: Sulfite is oxidized directly to provide electrons for electron transport and oxidative phosphorylation.Middle: Oxidation of sulfite resulting in its conversion to APS; this reaction produces electrons for ETC and oxidative phosphorylation; in addition, APS can drive ATP synthesis by substrate-level phosphorylation.Bottom: structure of APS (adenosine 5‘ phosphosulfate)
40 Reverse Electron Flow by Chemolithotrophs Calvin cycle requires NAD(P)H as electron source for fixing CO2many energy sources used by chemolithotrophs have E0 more positive than NAD+(P)/NAD(P)Huse reverse electron flow to generate NAD(P)HMetabolic Flexibility of Chemolithotrophsmany switch from chemolithotrophic metabolism to chemoorganotrophic metabolismmany switch from autotrophic metabolism (via Calvin cycle) to heterotrophic metabolism
41 Phototrophy photosynthesis energy from light trapped and converted to chemical energya two part processlight reactions in which light energy is trapped and converted to chemical energydark reactions in which the energy produced in the light reactions is used to reduce CO2 and synthesize cell constituentsoxygenic photosynthesis – eucaryotes and cyanobacteriaanoxygenic photosynthesis – all other bacteria
43 The Light Reaction in Oxygenic Photosynthesis photosynthetic eukaryotes and cyanobacteriaoxygen is generated and released into the environmentmost important pigments are chlorophylls
44 The Light Reaction in Oxygenic Photosynthesis chlorophylls葉綠素major light-absorbing pigmentsaccessory pigmentstransfer light energy to chlorophyllse.g., carotenoids類胡蘿蔔素and phycobiliproteins藻膽蛋白Chlorophyll structureDifferent chlorophylls have different absorption peaks
45 Accessory pigments absorb different wavelengths of light than chlorophylls Beta-carotene is a carotenoid found in algae and higher plants.Fucoxanthin is a carotenoid accessory pigment in several division s of algae (the dot in the structure represents a carbon atom).Phycocyanobilin is an example of a linear tetrapyrrole that is attached to a protein to form a phycobiliprotein.
46 Organization of pigments antennashighly organized arrays of chlorophylls and accessory pigmentscaptured light transferred to special reaction-center chlorophylldirectly involved in photosynthetic electron transportphotosystemsantenna and its associated reaction-center chlorophyllelectron flow PMF ATP
47 Oxygenic Photosynthesis noncyclicelectron flow –ATP + NADPHmade (noncyclicphotophos-phorylation)cyclic electronflow – ATPmade (cyclicphotophos-phorylation)Fd=ferredoxin; PQ=plastoquinone; PC=plastocyanin; Pheo. a=pheophytin a; PS I=photosystem I; PS II=photosystem II; OEC=oxygen evolving complex, extracts electrons from water and contains manganese ions and the substance Z, which transfers electrons to the PS II reaction center.
48 The Mechanism of Photosynthesis electron flow PMF ATPIllustration of chloroplast thylakoid membrane showing photosynthetic electron transport chain function and noncyclic photophosphorylation. The chain is composed of 3 complexes: PS I, the cytochrome bf complex, and PS II.Two diffusible electron carriers connect the 3 complexes. Plastoquinone (PQ) connects PS I with the cytochrome bf complex, and plastocyanin (PC) connects the cytochrome bf complex with PS II.
49 Purple nonsulfur bacteria, Rhodobacter sphaeroides The Light Reaction in Anoxygenic PhotosynthesisH2O not used as an electron source; therefore O2 is not producedonly one photosystem involveduses different pigments and mechanisms to generate reducing powercarried out by phototrophic green bacteria, phototrophic purple bacteria and heliobacteriaPurple nonsulfur bacteria, Rhodobacter sphaeroideselectron source forgeneration of NADHby reverse electron flowPhotosynthetic electron transport system of Rhodobacter sphaeroides. This scheme is incomplete and tentative. Ubiquinone (Q) is very similar to coenzyme Q. BPh=bacteriophytin.(similar to PSII)
50 Green sulfur bacteriaPhotosynthetic electron transport system of Chlorobium limicola. MK is the quinone menaquinone.(similar to PSI)Photosynthetic electron transport system of Chlorobium limicola. MK is the quinone menaquinone.
51 Bacteriorhodopsin-Based Phototrophy Some archaea use a type of phototrophy that involves bacteriorhodopsin, a membrane protein which functions as a light-driven proton pumpa proton motive force is generatedan electron transport chain is not involved