Microbiology Miniworkshop - Aalborg 3.pdfآ  4 Microbial Metabolism Enzymes -> Catalysators Enzymesare

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    Microbiology Miniworkshop

    3rd lecture: Chapter 8

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    Microbial Metabolism

    The Metabolism of Microbes

     metabolism – all chemical reactions and physical workings of a cell

     Two types of chemical reactions:

    • anabolism – biosynthesis; process that forms larger macromolecules from smaller molecules; requires energy input

    • catabolism – degradative; breaks the bonds of larger

    molecules forming smaller molecules; releases energy

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    Microbial Metabolism

    The Metabolism of Microbes

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    Microbial Metabolism

    Enzymes -> Catalysators

     Enzymes are biological catalysts that increase the rate of a chemical reaction by lowering the energy of activation. (no not interfere with the equilibrium of reaction)

     The enzyme is not permanently altered in the reaction.

     Enzyme promotes a reaction by serving as a physical site for specific substrate molecules to position.

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    Microbial Metabolism

    Enzymes -> Catalysators

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    Microbial Metabolism

    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 (Acetyl-CoA) – vitamins

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    Microbial Metabolism

    Co-factors

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    Microbial Metabolism

    Enzymes: Specificity and the Active Site

     Exhibits primary, secondary, tertiary, and some, quaternary structure

     Site for substrate binding is active site, or catalytic site

     A temporary enzyme-substrate union occurs when substrate moves into active site – induced fit

     Appropriate reaction occurs; product is formed and released

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    Microbial Metabolism

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    Microbial Metabolism

    Enzymes: Enzyme – Substrate Reactions

    ES complex ->

    transition state

    Induced fit -> enzyme adapts slightly -> more precise binding

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    Microbial Metabolism

    Enzymes: Location and Regularity of Enzyme Action

     Exoenzymes – transported extracellularly, where they break down large food molecules or harmful chemicals

    • cellulase, amylase, penicillinase

     endoenzymes – retained intracellularly and function there

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    Microbial Metabolism

    Enzymes: Location and Regularity of Enzyme Action

     Constitutive enzymes – always present, always produced in equal amounts or at equal rates, regardless of amount of substrate

    • enzymes involved in glucose metabolism

     Regulated enzymes – not constantly present; production is turned on (induced) or turned off (repressed) in response to changes in concentration of the substrate

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    Microbial Metabolism Enzymes:

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    Microbial Metabolism Enzymes: Synthesis and Hydrolysis Reactions

     Synthesis or condensation reactions – anabolic reactions to form covalent bonds between smaller substrate molecules, require ATP, release one molecule of water for each bond formed

     Hydrolysis reactions– catabolic reactions that break down substrates into small molecules; requires the input of water to break bonds

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    Microbial Metabolism Enzymes: Transfer Reactions

     Oxidation-reduction reactions – transfer of electrons • compound that loses electrons – oxidized

    • compound that gains electrons – reduced

     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

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    Microbial Metabolism

    Enzymes: Sensitivity to their Environment

     Temperature

     pH

     Osmotic pressure

     Organism’s habitat

    -> Changes induce instability

    Denaturation: non-covalent bonds are broken

    -> loss of structure and function

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    Microbial Metabolism

    Metabolic Pathways

     Sequence of metabolic reactions that proceed in a systematic, highly regulated manner – metabolic pathways

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    Microbial Metabolism

    Control of Enzyme Activity

     Competitive inhibition – substance that resembles normal substrate competes with substrate for active site

     Noncompetitive inhibition – enzymes are regulated by the binding of molecules other than the substrate on the 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

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    Microbial Metabolism

    Control of Enzyme Activity

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    Microbial Metabolism

    Control of Enzyme Activity

    -> enzyme induction/repression – enzymes are made only when suitable substrates are present

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    Microbial Metabolism

    The Pursuit and Utilization of Energy

     Energy – the capacity to do work or to cause change

     The ultimate source of energy is the sun (with the exception of certain chemoautotrophs).

    -> in the cell : Energy = chemical Energy (ATP)

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    Microbial Metabolism The Pursuit and Utilization of Energy: Cell Energetics

     Cells manage energy in the form of chemical reactions that make or break bonds and transfer electrons.

     Endergonic reactions – consume energy

     Exergonic reactions – release energy

     Energy present in chemical bonds of nutrients are trapped by specialized enzyme systems as the bonds of the nutrients are broken.

     Energy released is temporarily stored in high energy phosphate molecules (ATP). The energy of these molecules is used in endergonic cell reactions.

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    Microbial Metabolism The Pursuit and Utilization of Energy: Cell’s Energy Machine

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    Microbial Metabolism

    The Pursuit and Utilization of Energy: -> Biological Oxidation and Reduction

     Redox reactions - always occur in pairs

     There is an electron donor (reduced) and electron acceptor (oxidized) which constitute a redox pair.

     Process salvages electrons and their energy

     Released energy can be captured to phosphorylate ADP (-> ATP) or another compound.

    Electron and Proton Carriers:

     Repeatedly accept and release electrons and hydrogen to facilitate the transfer of redox energy

     Most carriers are coenzymes:

    NAD, FAD, NADP, coenzyme A and compounds of the respiratory chain

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    Microbial Metabolism

    The Pursuit and Utilization of Energy: -> Biological Oxidation and Reduction

    Reduction of NAD+

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    Microbial Metabolism

    The Pursuit and Utilization of Energy: -> Adenosine Triphosphate: ATP

     Three part molecule consisting of:

    • adenine – a nitrogenous base

    • ribose – a 5-carbon sugar

    • 3 phosphate groups

     ATP utilization and replenishment is a constant cycle in active cells.

     Removal of the terminal phosphate

    releases energy.

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    Microbial Metabolism

    The Pursuit and Utilization of Energy: -> Formation of ATP

    ATP can be formed by three different mechanisms:

     Substrate-level phosphorylation – transfer of phosphate group from a phosphorylated compound (substrate) directly to ADP

     Oxidative phosphorylation – series of redox reactions occurring during respiratory pathway

     Photophosphorylation – ATP is formed utilizing the energy of sunlight

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    Microbial Metabolism

    Pathways of Bioenergetics

     Bioenergetics – study of the mechanisms of cellular energy release and use

     Includes catabolic and anabolic reactions

     Primary catabolism of fuels (glucose) proceeds through a series of three coupled pathways:

    • glycolysis

    • tricarboxylic acid cycle, Kreb’s cycle

    • respiratory chain, electron transport

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    Microbial Metabolism

    Pathways of Bioenergetics

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    Microbial Metabolism

    Metabolic Strategies

     Nutrient processing is varied, yet in many cases is based on three catabolic pathways that convert glucose to CO2 and gives off energy (ATP).

     Aerobic respiration – glycolysis, the TCA cycle, respiratory chain; O2 final electron acceptor

     Anaerobic respiration - glycolysis, the TCA cycle, respiratory chain; molecular oxygen is not final electron acceptor

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