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Lecture 10

BLG 151 Lecture 10: Chapter 11 notes

13 Pages
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Department
Biology
Course Code
BLG 151
Professor
Martina Hausner

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Description
Microbiology Chapter 11: Catabolism Energy Release and Conservation (please review detailed information in textbook) 11.1 Metabolic Diversity and Nutritional Types Requirements for Carbon, Hydrogen, and Oxygen  Often satisfied together  Carbon source often provides H, O, and electrons  Heterotrophs:  use organic molecules as carbon sources which often also serve as energy source.  Can use a variety of carbon sources  Autotrophs:  Use carbon dioxide as their sole or principal carbon source  Must obtain energy from other sources Nutritional Types of Organisms  Based on energy source  Phototrophs: use light  Chemotrophs: obtain energy from oxidation of chemical compounds  Based on electron source  Lithotrophs: use reduced inorganic substances  Organotrophs: obtain electrons from organic compounds Classes of Major Nutritional Types  Majority of microorganisms known  Photolithoautotrophs (photoautotrophs)  Chemoorganoheterotrophs (chemoheterotrophs) - Majority of pathogens  Ecological importance  Photoorganoheterotrophs  Chemolithoautotrophs Fueling Reactions  Despite diversity of energy, electron, and carbon sources used by organisms, they all have the same basic needs  ATP as an energy currency  Reducing power to supply to supply electrons for chemical reactions  Precursor metabolites for biosynthesis Microorganisms May Change Nutritional Type  Some have great metabolic flexibility based on environmental requirements  Provides distinct advantage if environmental conditions change frequently Practice Question  When electrons flow from NAD+/NADH conjugate redox pair, does the reaction begin with NAD+ or with NADH? What is produced – O or H O? 2 2  Answer: i) NADH ii) H O2 o  In general terms, how is G related to E’o? o  Recall: G – standard free energy change at pH7: maximum amount of energy available for useful work under standard conditions  E’ - standard electron potential at pH7: measure of the tendency of the donor of a o half reaction to lose electrons; measure of potential energy  When electrons move from the donor to the acceptor, free energy is released and G of the reaction is directly related to the magnitude of the difference between the reduction potential of the two couples (o’ ): E’ois the E’oof the acceptor - E’oof the donor  The larger the E’othe greater the amount of free energy available 3+ 2+  What is the E’owhen electrons flow from NAD+/NADH redox pair to the Fe /Fe redox pair?  How does this compare to the E’ ohen electrons flow from Fe to Fe conjugate redox pair to the 1/22 / H2O pair?  Which will yield the largest amount of free energy to the cell? 11.2 There Are Three Chemo-organotrophic Fueling Processes Chemoorganotrophic Fueling Processes  Chemoorganotrophs are also called chemoheterotrophs  Processes  Aerobic respiration  Anaerobic respiration  Fermentation Chemoorganic Fueling Processes – Respiration  Respiration involves use of an electron transport chain  As electrons pass through the electron transport chain to the final electron acceptor, PMF is generated and used to synthesize most ATP by ox phos and a small amount by SLP Chemoorganic Fueling Processes – Respiration  Aerobic respiration  Final electron acceptor is oxygen  Anaerobic respiration  Final electron acceptor is different exogenous acceptor such as NO ,3SO , 4O , Fe2, or SeO 42-  Organic acceptors may also be used 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 the substrate-level phosphorylation (SLP) Energy Sources  Many different energy sources are funneled into common (but Few) degradative pathways  Having only few pathways that degrade many nutrients greatly increase metabolic efficiency  Most pathways generate glucose or intermediates of the pathways used in glucose metabolism and funnel metabolites into the glycolytic pathway or tricarboxylic acid cycle Catabolic Pathways  Enzyme catalyzed reactions whereby the product of one reaction serves as the substrate for the next  Pathways with enzymes that function both catabolically and anabolically also provide materials for biosynthesis – amphibolic pathways Amphibolic Pathways  Function both as catabolic and anabolic pathways  Important ones:  Embden-Meyerhof pathway (figure below)  Pentose phosphate pathway  Tricarboxylic acid (TCA) cycle Question  Is NAD+ reduced to NADH in the catabolic or anabolic direction of this pathway? 11.3 Aerobic Respiration Can Be Divided into Three Steps Aerobic Respiration  Process that can completely catabolize a reduced organic energy sour2e to CO using  Glycolytic pathways (glycolysis)  TCA cycle (Krebs)  Electron transport chain with oxygen as the final electron acceptor  Produces pyruvate, NADH, FADH 2r both  Partially oxidized carbon is fed into the TCA cycle and oxidized complet2ly to CO , some GTP or ATP, NADH and FADH wh2ch are oxidized in an electron transport chain to produce ATP 11.4 Glucose to Pyruvate: The First Step The Breakdown of Glucose to Pyruvate – The Bacterial Way!  Three common routes of catabolizing glucose to pyruvate – all glycolysis!  Embden-Meyerhof pathway  Pentose phosphate pathway  Entner-Duodoroff pathway The Embden-Meyerhof Pathway  Occurs in cytoplasmic matrix of most microorganisms, plants, and animals  The most common amphibolic pathway for glucose degradation to pyruvate  Provides precursor metabolites, NADH and ATP to the cell  Funtions in presence or absence of2O  Two phases:  Six carbon phase (6-C)  Three carbon phase (3-C) Six Carbon Phase:  ATP is used to phosphorylate glucose twice, adding phosphates to each end of the sugar  2 ATP is invested so that more ATP can be made later (‘priming the pump’) Three Carbon Phase:  Energy conserving phase, ATP and NADH are produced  ATP is made by SLP because ADP phosphorylation is coupled to exergonic hydrolysis of a high energy molecule, with a higher phosphate transfer potential than ATP (1,3- biphosphogylcerate) nd  A 2 ATP is made by SLP when phosphate on phosphoenolpyruvate is donated to ADP  Pyruvate is formed  4 ATP and 2 NADH per glucose are generated in this phase Summary of Glycolysis  Embden Meyerhoff  Most common  Important in anabolic pathways since it provides several precursor molecules  Occurs in cytoplasm  Produces 2 ATP (4 ATP from 3C phase minus 2 ATP from 6C phase), 2NADH (3C phase), 2H+ (3C phase), 2 pyruvate (3C phase) The Entner – Duodoroff Pathway  Used by some soil bacteria and a few other Gram – negative bacteria  Replaces the first phas
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