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1 Chapter 10 Catabolism : Energy Release and Conservation CHAPTER GLOSSARY Aerobic respiration Anaerobic respiration Anoxygenic photosynthesis ATP synthase.

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Presentation on theme: "1 Chapter 10 Catabolism : Energy Release and Conservation CHAPTER GLOSSARY Aerobic respiration Anaerobic respiration Anoxygenic photosynthesis ATP synthase."— Presentation transcript:

1 1 Chapter 10 Catabolism : Energy Release and Conservation CHAPTER GLOSSARY Aerobic respiration Anaerobic respiration Anoxygenic photosynthesis ATP synthase Bacteriochlorophyll Bacteriorhodopsin 紫紅質 Chemiosmotic hypothesis Chemolithotroph 營 Chlorophyll 葉綠素 Cyclic photophosphorylation Dark reactions Embden-Meyerhof pathway Entner-Doudoroff pathway Fermentation Glycolysis Light reactions Noncyclic photophosphorylation Oxidative phosphorylation Oxygenic photosynthesis Pentose phosphate pathway Photophosphorylation Photosynthesis Proton motive force (PMF) Substrate-level phosphorylation Tricarboxylic acid (TCA) cycle

2 2 Chemoorganotrophic fueling processes also called chemoheterotrophs processes  aerobic respiration  anaerobic respiration  fermentation

3 3 Chemoorganic fueling processes-respiration most respiration involves use of an electron transport chain as electrons pass through the electron transport chain to the final electron acceptor, a proton motive force (PMF) is generated and used to synthesize ATP aerobic respiration final electron acceptor is oxygen anaerobic respiration  final electron acceptor is different exogenous acceptor such as NO 3-, SO 4 2-, CO 2, Fe 3+, or SeO 4 2-  organic acceptors may also be used ATP made primarily by oxidative phosphorylation

4 4 Chemoorganic fueling processes - fermentation uses an endogenous electron acceptor  usually an intermediate of the pathway used to oxidize the organic energy source e.g., pyruvate does not involve the use of an electron transport chain nor the generation of a proton motive force ATP synthesized only by substrate-level phosphorylation

5 5 Energy Sources many different energy sources are funneled into common degradative pathways most pathways generate glucose or intermediates of the pathways used in glucose metabolism few pathways greatly increase metabolic efficiency

6 6 Amphibolic Pathways function both as catabolic and anabolic pathways important ones  Embden-Meyerhof pathway  pentose phosphate pathway  tricarboxylic acid (TCA) cycle Catabolic Pathways enzyme catalyzed reactions whereby the product of one reaction serves as the substrate for the next pathways also provide materials for biosynthesis amphibolic 有二義的 pathways

7 7 Aerobic Respiration process that can completely catabolize an organic energy source to CO 2 using  glycolytic pathways (glycolysis)  TCA cycle  electron transport chain with oxygen as the final electron acceptor produces ATP, and high energy electron carriers

8 8 The Breakdown of Glucose to Pyruvate Three common routes  Embden-Meyerhof pathway  Entner-Doudoroff pathway  pentose phosphate pathway The Embden-Meyerhof Pathway glucose + 2ADP + 2P i + 2NAD + ↓ 2 pyruvate + 2ATP + 2NADH + 2H + occurs in cytoplasmic matrix of most microorganisms, plants, and animals the most common pathway for glucose degradation to pyruvate in stage two of aerobic respiration function in presence or absence of O 2 two phases

9 9 addition of phosphates “primes the pump” oxidation step – generates NADH high-energy molecules – used to synthesize ATP by substrate-level phosphorylation The Embden-Meyerhof Pathway

10 10 The Entner-Doudoroff Pathway yield per glucose molecule:  1 ATP  1 NADPH  1 NADH reactions of Embden- Meyerhof Pathway reactions of Entner- Doudoroff Pathway used by soil bacteria and a few gram-negative bacteria replaces the first phase of the Embden-Meyerhof pathway

11 11 The Pentose Phosphate Pathway also called hexose monophosphate pathway can operate at same time as glycolytic pathway or Entner-Doudoroff pathway can operate aerobically or anaerobically an amphibolic pathway glucose-6-P + 12NADP + + 7H 2 O  6CO NADPH + 12H + P i Summary of pentose phosphate pathway

12 12 Oxidation steps Produce NADPH, which is needed for biosynthesis sugar trans- formation reactions produce sugars needed for biosynthesis sugars can also be further degraded The Pentose Phosphate Pathway

13 13 The Tricarboxylic Acid Cycle also called citric acid cycle and Kreb’s cycle common in aerobic bacteria, free-living protozoa, most algae, and fungi major role is as a source of carbon skeletons for use in biosynthesis for each acetyl-CoA molecule oxidized, TCA cycle generates:  2 molecules of CO 2  3 molecules of NADH  one FADH 2  one GTP

14 14 Electron Transport and Oxidative Phosphorylation only 4 ATP molecules synthesized directly from oxidation of glucose to CO 2 most ATP made when NADH and FADH 2 (formed as glucose degraded) are oxidized in electron transport chain (ETC) Electron Transport Chains the mitochondrial electron transport chain (ETC) is composed of a series of electron carriers that operate together to transfer electrons from NADH and FADH 2 to a terminal electron acceptor, O 2 electrons flow from carriers with more negative reduction potentials (E 0 ) to carriers with more positive E 0

15 15 The Electron Transport Chain large difference in E 0 of NADH and E 0 of O 2 large amount of energy released each carrier is reduced and then reoxidized carriers are constantly recycled the difference in reduction potentials electron carriers, NADH and O 2 is large, resulting in release of great deal of energy

16 16 Mitochondrial ETC in eukaryotes the electron transport chain carriers are within the inner mitochondrial membrane and connected by coenzyme Q and cytochrome c electron transfer accompanied by proton movement across inner mitochondrial membrane

17 17 located in plasma membrane some resemble mitochondrial ETC, but many are different  different electron carriers  may be branched  may be shorter  may have lower P/O ratio Bacterial and Archaeal ETCs Paracoccus denitrificans facultative, soil bacterium extremely versatile metabolically under oxic conditions, uses aerobic respiration  similar electron carriers and transport mechanism as mitochondria  protons transported to periplasmic space rather than inner mitochondrial membrane  can use one carbon molecules instead of glucose

18 18 upper branch – stationary phase and low aeration lower branch – log phase and high aeration 通風 Electron Transport Chain of E. coli branched pathway Different array of cytochromes used than in mitochondrial

19 19 Oxidative Phosphorylation Process by which ATP is synthesized as the result of electron transport driven by the oxidation of a chemical energy source Chemiosmotic hypothesis the most widely accepted hypothesis to explain oxidative phosphorylation  electron transport chain organized so protons move outward from the mitochondrial matrix as electrons are transported down the chain  proton expulsion during electron transport results in the formation of a concentration gradient of protons and a charge gradient  the combined chemical and electrical potential difference make up the proton motive force (PMF)

20 20 The Q Cycle

21 21 PMF drives ATP synthesis Importance of PMF diffusion of protons back across membrane (down gradient) drives formation of ATP ATP synthase  enzyme that uses PMF down gradient to catalyze ATP synthesis  functions like rotary engine with conformational changes

22 22 ATP synthase structure and function

23 23 ATP Yield During Aerobic Respiration maximum ATP yield can be calculated  includes P/O ratios of NADH and FADH 2  ATP produced by substrate level phosphorylation the theoretical maximum total yield of ATP during aerobic respiration is 38  the actual number closer to 30 than 38

24 24 Theoretical vs. Actual Yield of ATP amount of ATP produced during aerobic respiration varies depending on growth conditions and nature of ETC under anaerobic conditions, glycolysis only yields 2 ATP molecules Factors Affecting ATP Yield bacterial ETCs are shorter and have lower P/O ratios ATP production may vary with environmental conditions PMF in bacteria and archaea is used for other purposes than ATP production (flagella rotation) precursor metabolite may be used for biosynthesis

25 25 Anaerobic Respiration uses electron carriers other than O 2 generally yields less energy because E 0 of electron acceptor is less positive than E 0 of O 2

26 26 An Example… dissimilatory 異化 nitrate reduction  use of nitrate as terminal electron acceptor  the anaerobic reduction of nitrate makes it unavailable to cell for assimilation ( 同化, 吸收 ) or uptake denitrification  reduction of nitrate to nitrogen gas  in soil, causes loss of soil fertility ETC of Paracoccus denitrificans - anaerobic

27 27 Fermentation oxidation of NADH produced by glycolysis pyruvate or derivative used as endogenous electron acceptor substrate only partially oxidized oxygen not needed oxidative phosphorylation does not occur  ATP formed by substrate-level phosphorylation

28 28 homolactic fermenters heterolactic fermenters food spoilage alcoholic fermentation alcoholic beverages, bread, etc. yogurt, sauerkraut 德國泡菜, pickles 泡菜, etc.

29 29

30 30 Catabolism of Other Carbohydrates many different carbohydrates can serve as energy source carbohydrates can be supplied externally or internally (from internal reserves) monosaccharides  converted to other sugars that enter glycolytic pathway disaccharides and polysaccharides  cleaved by hydrolases or phosphorylases

31 31 Reserve Polymers used as energy sources in absence of external nutrients  e.g., glycogen and starch cleaved by phosphorylases (glucose) n + P i  (glucose) n-1 + glucose-1-P glucose-1-P enters glycolytic pathway  e.g., Poly-  -hydroxybutyrate (PHB) the soil bacterium Azotobacter PHB    acetyl-CoA acetyl-CoA enters TCA cycle

32 32 Lipid Catabolism triglycerides  common energy sources  hydrolyzed to glycerol and fatty acids by lipases glycerol degraded via glycolytic pathway fatty acids often oxidized via β-oxidation pathway

33 33 β-oxidation pathway

34 34 Protein and Amino Acid Catabolism transfer of amino group from one amino acid to α-keto acid protease  hydrolyzes protein to amino acids deamination  removal of amino group from amino acid  resulting organic acids converted to pyruvate, acetyl-CoA, or TCA cycle intermediate can be oxidized via TCA cycle can be used for biosynthesis  can occur through transamination

35 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 molecule  transferred to terminal electron acceptor (usually O 2 ) by ETC ATP synthesized by oxidative phosphorylation

36 36 Energy Sources bacterial and archaeal species have specific electron donor and acceptor preferences much less energy is available from oxidation of inorganic molecules than glucose oxidation due to more positive redox potentials

37 37 Three Major Groups of Chemolithotrophs have ecological importance several bacteria and archaea oxidize hydrogen sulfur-oxidizing microbes  hydrogen sulfide (H 2 S), sulfur (S 0 ), thiosulfate (S 2 O 3 2- ) nitrifying bacteria oxidize ammonia to nitrate

38 38 Sulfur-oxidizing bacteria ATP can be synthesized by both oxidative phosphorylation and substrate-level phosphorylation

39 39 Nitrifying Bacteria Example requires 2 different genera oxidize ammonia to nitrate NH 4 +  NO 2 -  NO 3 -

40 40 Reverse Electron Flow by Chemolithotrophs Calvin cycle requires NAD(P)H as electron source for fixing CO 2  many energy sources used by chemolithotrophs have E 0 more positive than NAD + (P)/NAD(P)H use reverse electron flow to generate NAD(P)H Metabolic Flexibility of Chemolithotrophs many switch from chemolithotrophic metabolism to chemoorganotrophic metabolism many switch from autotrophic metabolism (via Calvin cycle) to heterotrophic metabolism

41 41 Phototrophy photosynthesis  energy from light trapped and converted to chemical energy  a two part process light reactions in which light energy is trapped and converted to chemical energy dark reactions in which the energy produced in the light reactions is used to reduce CO 2 and synthesize cell constituents oxygenic photosynthesis – eucaryotes and cyanobacteria anoxygenic photosynthesis – all other bacteria

42 42 Phototrophic fueling reactions

43 43 photosynthetic eukaryotes and cyanobacteria oxygen is generated and released into the environment most important pigments are chlorophylls The Light Reaction in Oxygenic Photosynthesis

44 44 The Light Reaction in Oxygenic Photosynthesis chlorophylls 葉綠素  major light-absorbing pigments accessory pigments  transfer light energy to chlorophylls  e.g., carotenoids 類胡蘿蔔素 and phycobiliproteins 藻膽蛋白 Different chlorophylls have different absorption peaks Chlorophyll structure

45 45 Accessory pigments absorb different wavelengths of light than chlorophylls

46 46 Organization of pigments antennas  highly organized arrays of chlorophylls and accessory pigments  captured light transferred to special reaction-center chlorophyll directly involved in photosynthetic electron transport photosystems  antenna and its associated reaction-center chlorophyll electron flow  PMF  ATP

47 47 noncyclic electron flow – ATP + NADPH made (noncyclic photophos- phorylation) cyclic electron flow – ATP made (cyclic photophos- phorylation) Oxygenic Photosynthesis

48 48 electron flow  PMF  ATP The Mechanism of Photosynthesis

49 49 Purple nonsulfur bacteria, Rhodobacter sphaeroides The Light Reaction in Anoxygenic Photosynthesis H 2 O not used as an electron source; therefore O 2 is not produced only one photosystem involved uses different pigments and mechanisms to generate reducing power carried out by phototrophic green bacteria, phototrophic purple bacteria and heliobacteria (similar to PSII) electron source for generation of NADH by reverse electron flow

50 50 Green sulfur bacteria (similar to PSI) Photosynthetic electron transport system of Chlorobium limicola. MK is the quinone menaquinone.

51 51 Bacteriorhodopsin-Based Phototrophy Some archaea use a type of phototrophy that involves bacteriorhodopsin, a membrane protein which functions as a light-driven proton pump a proton motive force is generated an electron transport chain is not involved


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