Microbial Metabolism
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Microbial Metabolism






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    Microbial Metabolism Microbial Metabolism Presentation Transcript

    • Foundations in Microbiology Chapter 8 PowerPoint to accompany Fifth Edition Talaro Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
    • Microbial Metabolism: The Chemical Crossroads of Life Chapter 8
    • Metabolism The sum total of all chemical reactions & physical workings occurring in a cell
    • 2 types of metabolism
      • Anabolism - biosynthesis
        • building complex molecules from simple ones
        • requires energy (ATP)
      • Catabolism - degradation
        • breaking down complex molecules into simple ones
        • generates energy (ATP)
    • Enzyme structure
      • Simple enzymes – consist of protein alone
      • Conjugated enzymes or holoenzymes – contain protein and nonprotein molecules
        • apoenzyme –protein portion
        • cofactors – nonprotein portion
          • metallic cofactors – iron, copper, magnesium
          • coenzymes -organic molecules - vitamins
    • Enzyme-substrate interactions
      • Exoenzymes – transported extracellularly, where they break down large food molecules or harmful chemicals; cellulase, amylase, penicillinase
      • Endoenzymes – retained intracellularly & function there
      • Constitutive enzymes – always present, always produced in equal amounts or at equal rates, regardless of amount of substrate; enzymes involved in glucose metabolism
      • Induced enzymes – not constantly present, produced only when substrate is present, prevents cell from wasting resources
      • Synthesis or condensation reactions – anabolic reactions to form covalent bonds between smaller substrate molecules, require ATP, release one molecule of water for each bond
      • Hydrolysis reactions – catabolic reactions that break down substrates into small molecules, requires the input of water
    • Transfer reactions by enzymes
      • Oxidation-reduction reactions – transfer of electrons
      • Aminotransferases – convert one type of amino acid to another by transferring an amino group
      • Phosphotransferases – transfer phosphate groups, involved in energy transfer
      • Methyltransferases – move methyl groups from one molecule to another
      • Decarboxylases – remove carbon dioxide from organic acids
    • Metabolic pathways
    • Control of enzyme activity
      • Competitive inhibition – substance that resembles normal substrate competes with substrate for active site
      • Feedback inhibition – concentration of product at the end of a pathway blocks the action of a key enzyme
      • Feedback repression – inhibits at the genetic level by controlling synthesis of key enzymes
      • Enzyme induction – enzymes are made only when suitable substrates are present
    • Competitive inhibition
    • Energy –capacity to do work or cause change
      • Endergonic reactions – consume energy
      • Exergonic reactions – release energy
    • Redox reactions
      • always occur in pairs
      • There is an electron donor and electron acceptor which constitute a redox pair
      • The process salvages electrons & their energy.
      • released energy can be captured to phosphorylate ADP or another compound
    • Electron carriers
      • resemble shuttles that are loaded and unloaded with electrons and hydrogen
      • most carriers are coenzymes, NAD, FAD, NADP, coenzyme A & compounds of the respiratory chain
    • NAD reduction
    • Electron carriers
    • ATP
      • 3 part molecule consisting of
        • adenine – a nitrogenous base
        • ribose – a 5-carbon sugar
        • 3 phosphate groups
      • Removal of the terminal phosphate releases energy
    • ATP
    • Phosphorylation of glucose by ATP
    • Formation of ATP
      • substrate-level phosphorylation
      • oxidative phosphorylation
      • photophosphorylation
    • substrate-level phosphorylation
    • Catabolism of glucose
      • Glycolysis
      • Tricarboxylic acid cycle, Kreb’s cycle
      • Respiratory chain, electron transport
    • Metabolic strategies 2 Organic molecules Glycolysis Fermentation variable NO 3 - , So 4 -2 , CO 3 -3 Glycolysis, TCA, ET Anaerobic respiration 38 O 2 Glycolysis, TCA, ET Aerobic respiration ATP yield Final e- acceptor Pathways involved
    • Overview of aerobic respiration
    • Overview of aerobic respiration
      • Glycolysis – glucose (6C) is oxidized and split into 2 molecules of pyruvic acid (3C)
      • TCA – processes pyruvic acid and generates 3 CO 2 molecules
      • Electron transport chain – accepts electrons NADH & FADH, generates energy through sequential redox reactions called oxidative phosphorylation
    • Glycolysis
    • TCA cycle
    • Electron transport system
    • Chemiosmosis
    • Fermentation
      • Incomplete oxidation of glucose or other carbohydrates in the absence of oxygen
      • Uses organic compounds as terminal electron acceptors
      • Yields a small amount of ATP
      • Production of ethyl alcohol by yeasts acting on glucose
      • Formation of acid, gas & other products by the action of various bacteria on pyruvic acid
    • Fermentation
    • Products of fermentation
      • Many pathways of metabolism are bi-directional or amphibolic
      • Metabolites can serve as building blocks or sources of energy
        • Pyruvic acid can be converted into amino acids through amination
        • Amino acids can be converted into energy sources through deamination
        • Glyceraldehyde-3-phosphate can be converted into precursors for amino acids, carbohydrates and fats