Microbial Metabolism & Catabolism Lecture Notes PDF

Lecture 7 Metabolism and Catabolism Microbes transfer energy by moving electrons from: – Reduced food molecules (glucose) --> We will begin where we left off, so bring dif...

Lecture 7 Metabolism and Catabolism Microbes transfer energy by moving electrons from: – Reduced food molecules (glucose) --> We will begin where we left off, so bring diffusible carriers in cytoplasm --> outline from last time. membrane-bound carriers --> O2, metals or oxidized forms of N and S Reading: Chapter 11 Sects 1 - 6 – Energy yielding reactions are a part of metabolism called catabolism and are grouped into several nutritional classes. 1 2 Earth s Life Forms are Carbon Based - In addition, all organisms require sources Carbon Cycle Involves 2 Metabolic Groups of energy for growth Autotrophs – CO2 as C source (plants, many microbes) Phototrophs - light – synthesize organic compounds used by heterotrophs Chemotrophs - oxidize chemical compounds – also called primary producers (often same as their C source) Heterotrophs – reduced, preformed organic compounds as C source (animals, many microbes) – convert large amounts of C to CO2 3 4 As well as electrons Nutritional Types of Organisms Almost all Eukarya are either reu - Lithotrophs - inorganic molecules as electron donors photoautotrophs (plants and algae) or heterotrophs (animals, protozoa, fungi) Organotrophs - organic molecules as donors Lithotrophy unique to a few Bacteria and Archaea (prokaryotes) 5 6 1  0:00 Organotrophs: Organic Molecules as Energy Sources Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. You should be able to use Table 11.1 and information from lecture to describe the Many different energy nutritional needs of microbes. sources are funneled into common degradative pathways Most pathways generate glucose or Example: Photoorganoheterotroph intermediates of the pathways used in Energy? Light organic compound I glucose metabolism Electrons? Organic compound ATP by 2 means: Carbon? Carbon source Substrate Level Phosphorylation Oxidative 7 8 Phosphorylation Aerobic Respiration Embden-Meyerhof (glycolysis) Process that can completely catabolize an organic energy source to CO2 using: most common form of glucose breakdown Occur in cytoplasm Glycolytic pathways (Glycolysis) Function in presence or absence of O2 Ten reactions, in two stages Tricarboxylic Acid Cycle (also called Kreb’s Cycle or Citric Acid Cycle) Electron transport chain with oxygen as final electron acceptor Produces ATP (most indirectly, via electron transport) 9 10 08 : 30 Glycolysis What start ? w endw G Glycolysis is Glycolysis: NADH and ATP Generating Steps an Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2 amphibolic pathway 6 C Stage: glucose phosphorylated twice (requires ATP) generating fructose 1,6-bisphosphate ↳ Functions both and anabolically catabolically Reaction 1 Glyceraldehyde-3- phosphate oxidized and - phosphorylated - G3P 7 enzyme 3 C Stage: Fructose 1,6-bisphosphate XX generates high-energy P bond dehydrogenase S split into 2 glyceraldehyde NAD+ reduced to NADH 3-P then converted to pyruvate Key reactions Reaction 2 Phosphorylation of ADP 3PG Kinase oxidation -> NADH by high energy Substrate-level metabolic substrate Generates ATP by phosphorylation -> ATP substrate level Net yield: 2 ATP, 2 NADH, w phosphorylation 11 end t end 2 pyruvate 2  Glycolysis: NADH and ATP Generating Steps Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Tricarboxylic Acid (Citric Acid or Kreb s) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cycle Pyruvate completely oxidized to CO2 The last reaction of glycolysis is also a Substrate-Level In mitochondria of eukaryotes, cytoplasm Phosphorylation pyruvate prokaryotes Kinase Generate: What enzyme CO2 catalyzes this reaction? Numerous NADH and FADH2 (another diffusible e- carrier) kinase Precursors for biosynthesis Pyruvate 14 Pyruvate first oxidized The TCA Cycle a CO2 and Acetyl CoA Electron Transport and Oxidative More Phosphorylation oxidations (Acetyl CoA has high form NADH and energy thioester bond) FADH2 There is only a net yield of 2 ATP molecules synthesized directly from Acetyl CoA condensed oxidation of glucose with oxaloacetate Most ATP made when NADH and FADH2 Succinyl-CoA to Succinate Oxidation and decarboxylation rxns forming are oxidized in electron transport chains NADH and CO2 Generate high energy guanosine tri phosphate (GTP) Figure 11.8 16 via SLP 28:48 Electron Transport Chains Electron Transport Chains Electrons from NADH and FADH2 generated by Found in mitochondrial membrane in Eukarya, the oxidation of organic substrates (during plasma membrane in Bacteria and Archaea glycolysis and the TCA cycle) are transferred through a series of membrane bound electron Electron carriers: Cytochromes and Quinones carriers to a final terminal electron acceptor. Electrons flow from carriers with more negative E0 to more positive E0 - energy is released and nu memorize used to make ATP by oxidative phosphorylation. C 3 ATP can be generated per NADH using O2 as terminal electron acceptor 17 18 carrier with > - more positive more re receptor - 3 32:25 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Oxidative Phosphorylation PMF Drives ATP Synthesis Chemiosmotic Hypothesis e- flow causes protons to move outward across membrane, ATP – energy released during e- transport used to establish proton gradient made when they move back in and charge difference across membrane F1Fo ATP Synthase Proton Motive Force (PMF) –Multiprotein complex, uses proton movement to catalyze ATP synthesis 19 20 ETC Generates a PMF for ATP Synthesis Bacterial F1Fo ATP Synthase Proton channel Election Transport Chain - > H+ > f Fo - · · a subunit - proton channel Plasma C subunits rotates Membrane ring of - · subunit sub unit turn when H +. F more in rotates Is shaft · the Cytoplasm chanel Conformational changes · in ADP movement of ATP synthase sphere of G , B subunits use protor protons Figure 9.19a (t established flow down ATP ~ ATP synthesis gradient to OMF make ATP 40 35 : Microbes vary in terms of electron Anaerobic Respiration Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. acceptors they use no memorize I Less ATP than aerobic, why? See pg 236 Anaerobic Hood 23 24 because it uses alternative electron acceptors with lower redox potentials, resulting in a lower energy yield from the electron transport chain. This leads to fewer protons being pumped across the membrane, a weaker proton motive force, and consequently, fewer ATP molecules being synthesized. 4  Anaerobic Respiration Example Denitrification – Nitrate (NO 3-) as terminal electron acceptor – Reduced to nitrogen gas (N 2) – Paracoccus denitrificans – Facultative anaerobe in soil – Depletes soil N, lower crop yield Escherichia coli (Facultative anaerobe) can also use Nitrate as e- acceptor Nitrate first reduced to Nitrite Basis of Nitrite Strip Test - diagnostic for Urinary Tract Infections (UTI) 25 5