Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 Chapter 9 Metabolism: Energy Release and Conservation

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2 Sources of energy most microorganisms use one of three energy sources the sun reduced organic compounds reduced inorganic compounds the chemical energy obtained can be used to do work Figure 9.1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3 Chemoorganotrophic fueling processess Figure 9.2

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4 Chemoorganic fueling processes-respiration most respiration involves use of an electron transport chain 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 –organic acceptors may also be used 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6 Overview of aerobic catabolism three-stage process –large molecules (polymers)  small molecules (monomers) –initial oxidation and degradation to pyruvate –oxidation and degradation of pyruvate by the tricarboxylic acid cycle (TCA cycle)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7 many different energy sources are funneled into common degradative pathways ATP made primarily by oxidative phosphory- lation Figure 9.3

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8 Amphibolic Pathways function both as catabolic and anabolic pathways important ones –Embden-Meyerhof pathway –pentose phosphate pathway –tricarboxylic acid (TCA) cycle Figure 9.4

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9 The Breakdown of Glucose to Pyruvate Three common routes –Embden-Meyerhof pathway –pentose phosphate pathway –Entner-Doudoroff pathway

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 10 The Embden-Meyerhof Pathway occurs in cytoplasmic matrix of both procaryotes and eucaryotes the most common pathway for glucose degradation to pyruvate in stage two of aerobic respiration

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 11 Figure 9.5 addition of phosphates “primes the pump” oxidation step – generates NADH high-energy molecules – used to synthesize ATP by substrate-level phosphorylation

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 12 Summary of glycolysis glucose + 2ADP + 2P i + 2NAD +  2 pyruvate + 2ATP + 2NADH + 2H +

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14 oxidation steps produce NADPH, which is needed for biosynthesis sugar trans- formation reactions produce sugars needed for biosynthesis sugars can also be further degraded Figure 9.6

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 15 Figure 9.7

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16 Summary of pentose phosphate pathway glucose-6-P + 12NADP + + 7H 2 O  6CO NADPH + 12H + P i

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17 The Entner-Doudoroff Pathway yield per glucose molecule: –1 ATP –1 NADPH –1 NADH reactions of glycolytic pathway reactions of pentose phosphate pathway Figure 9.8

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 19 Figure 9.9

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20 Summary for each acetyl-CoA molecule oxidized, TCA cycle generates: –2 molecules of CO 2 –3 molecules of NADH –one FADH 2 –one GTP

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21 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)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22 The Electron Transport Chain series of electron carriers that operate together to transfer electrons from NADH and FADH 2 to a terminal electron acceptor electrons flow from carriers with more negative E 0 to carriers with more positive E 0

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 23 Electron transport chain… as electrons transferred, energy released in eucaryotes the electron transport chain carriers are within the inner mitochrondrial membrane

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24 Mitochondrial ETC electron transfer accompanied by proton movement across inner mitochondrial membrane Figure 9.11

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 25 Procaryotic ETCs 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26 Electron Transport Chain of E. coli branched pathway upper branch – stationary phase and low aeration lower branch – log phase and high aeration Figure 9.12

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 27 Oxidative Phosphorylation Process by which ATP is synthesized as the result of electron transport driven by the oxidation of a chemical energy source

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 28 Chemiosmotic hypothesis is 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)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 29 PMF drives ATP synthesis diffusion of protons back across membrane (down gradient) drives formation of ATP ATP synthase –enzyme that uses PMF down gradient to catalyze ATP synthesis

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 30 Inhibitors of ATP synthesis blockers –inhibit flow of electrons through ETC uncouplers –allow electron flow, but disconnect it from oxidative phosphorylation –many allow movement of ions, including protons, across membrane without activating ATP synthase destroys pH and ion gradients –some may bind ATP synthase and inhibit its activity directly

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 31 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 32 Maximum Theoretic ATP Yield from Aerobic Respiration Figure 9.15

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 33 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 34 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 Table 9.1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 35 Microbial Fermentations 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 36 Fermentations Figure 9.17

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 37 homolactic fermenters heterolactic fermenters food spoilage yogurt, sauerkraut, pickles, etc. alcoholic fermentation alcoholic beverages, bread, etc. Figure 9.18

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 38 Table 9.2

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 39 Fermentations of amino acids Stickland reaction –oxidation of one amino acid with use of second amino acid as electron acceptor –carried out by some Clostridium spp. Figure 9.19

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 40 Catabolism of Carbohydrates and Intracellular Reserves many different carbohydrates can serve as energy source carbohydrates can be supplied externally or internally (from internal reserves)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 41 Carbohydrates monosaccharides –converted to other sugars that enter glycolytic pathway disaccharides and polysaccharides –cleaved by hydrolases or phosphorylases Figure 9.20

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 42 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., PHB PHB    acetyl-CoA acetyl-CoA enters TCA cycle

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 43 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 Figure 9.21

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 44 β-oxidation pathway Figure 9.22

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 45 Protein and Amino Acid Catabolism 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 46 deamination often occurs by transamination transfer of amino group from one amino acid to α-keto acid Figure 9.23

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 47 Chemolithotrophy carried out by chemolithotrophs 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 48 Figure 9.24

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 49 Table 9.3

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 50 Table 9.4

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 51 Nitrifying bacteria oxidize ammonia to nitrate NH 3  NO 2  NO 3 requires 2 different genera Figure 9.25

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 52 Sulfur-oxidizing bacteria ATP can be synthesized by both oxidative phosphorylation and substrate- level phosphorylation Figure 9.26

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 53 Autotrophic growth by chemolithotrophs Calvin cycle requires NADH as electron source for fixing CO 2 –many energy sources used by chemolithotrophs have E 0 more positive than NAD/NADH use reverse electron flow to generate NADH

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 54 Metabolic flexibility of chemolithotrophs many switch from chemolithotrophic metabolism to chemoorganotrophic metabolism many switch from autotrophic metabolism (via Calvin cycle) to heterotrophic metabolism

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 55 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 56 oxygenic photosynthesis – eucaryotes and cyanobacteria anoxygenic photosynthesis – all other bacteria Table 9.5

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 57 Figure 9.27

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 58 The Light Reaction in Oxygenic Photosynthesis chlorophylls –major light-absorbing pigments accessory pigments –transfer light energy to chlorophylls –e.g., carotenoids and phycobiliproteins

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 59 different chlorophylls have different absorption peaks Figure 9.28

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 60 Accessory pigments absorb different wavelengths of light than chlorophylls Figure 9.29

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 61 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 62 Green plant photosynthesis noncyclic electron flow – ATP + NADPH made (noncyclic photophos- phorylation) cyclic electron flow – ATP made (cyclic photophos- phorylation) Figure 9.30

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 63 electron flow  PMF  ATP Figure 9.31

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 64 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 65 A Photosynthetic Reaction Chain Figure 9.32

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 66 Purple nonsulfur bacteria electron source for generation of NADH by reverse electron flow Figure 9.33

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 67 Green sulfur bacteria Figure 9.34

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 68 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