Chapter 5. Microbial Metabolism

Transcription

1 Chapter 5 Microbial Metabolism

2 Metabolism Collection of controlled biochemical reactions that take place within a microbe Ultimate function of metabolism is to reproduce the organism

3 Metabolic Processes Guided by 8 Elementary Statements 1) Every cell acquires nutrients 2) Metabolism requires energy from light or catabolism of nutrients 3) Energy is stored in adenosine triphosphate (ATP) 4) Cells catabolize nutrients to form precursor metabolites 5) Precursor metabolites, energy from ATP, and enzymes are used in anabolic reactions 6) Enzymes plus ATP form macromolecules 7) Cells grow by assembling macromolecules 8) Cells reproduce once they have doubled in size

4 The metabolism of microbes Metabolism sum of all chemical reactions that help cells function Two types of chemical reactions Catabolism -degradative breaks the bonds of larger molecules forming smaller molecules; releases energy, Anabolism biosynthesis forms larger macromolecules from smaller molecules requires energy input end products: proteins etc. end products: CO 2, H 2 O

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6 Types of energy Energy: the capacity to do work or to cause change Forms of energy include Thermal Radiant/ Light Electrical Mechanical Atomic Chemical Only photosynthetic autotrophs can utilize light energy directly Photosynthesis converts light into chemical energy Provides nutritional and energy basis for all heterotrophs

7 Cell energetics Cells manage energy in the form of chemical reactions that make or break bonds and transfer electrons Reactions Exergonic Enzyme A + B C + Energy Release energy Energy released is temporarily stored in ATP Energy+ Endergonic Enzyme A + B C Consume energy The energy in ATP is used in endergonic cell reactions

8 Cell energetics Reactions Synthesis/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 water to break bonds may releases ATP

9 Metabolism is composed of catabolic and anabolic reactions. Figure 5.1

10 Oxidation and Reduction Reactions Transfer of electrons from an electron donor to an electron acceptor Reactions always occur simultaneously Cells use electron carriers to carry electrons (often in H atoms) Three important electron carriers 1) Nicotinamide adenine dinucleotide (NAD + ) 2) Nicotinamide adenine dinucleotide phosphate (NADP + ) 3) Flavin adenine dinucleotide (FAD)

11 Oxidation-reduction, or redox, reactions. Loss of electron = oxidation Gain of electron = reduction Figure 5.2

12 Adenosine Triphosphate (ATP) Metabolic currency Three part molecule consisting of: Adenine nitrogenous base Ribose 5-carbon sugar 3 phosphate groups adenosine = no phosphates adenosine monophosphate (AMP) = adenosine + 1 phosphate adenosine diphosphate (ADP) = adenosine + 2 phosphates adenosine triphosphate (ATP) = adenosine + 3 phosphates Removal of the terminal phosphate releases energy

13 ATP Production and Energy Storage Phosphorylation inorganic phosphate is added to substrate Cells phosphorylate ADP to ATP in three ways: 1) Substrate-level phosphorylation 2) Oxidative phosphorylation 3) Photophosphorylation

14 You are expected to know What are enzymes Enzyme Structure Enzyme examples and their cofactors Location of enzyme Action Regulation of enzyme Action Sensitivity of enzymes to their environment Competitive & non competitive inhibition of enzymes

15 Bioenergetics pathways Bioenergetics studying mechanisms of cellular energy reserve management Includes catabolic and anabolic reactions Primary catabolism of fuels (glucose) proceeds through a series of three coupled pathways: 1. Glycolysis 2. Kreb s cycle 3. Respiratory chain, electron transport

16 Carbohydrate Catabolism Many organisms oxidize carbohydrates as primary energy source for anabolic reactions Glucose most common carbohydrate used Glucose catabolized by two processes: Cellular respiration Fermentation

17 Metabolic strategies Processing nutrients in many cases is based on three catabolic pathways that convert glucose to CO 2 and gives off energy Aerobic respiration glycolysis Kreb s cycle respiratory chain Anaerobic respiration glycolysis Kreb s cycle respiratory chain Fermentation glycolysis Final electron acceptor: Oxygen Not Oxygen but sulfate (SO 4 2- ), nitrate (NO 3- ) organic compounds

18 Summary of glucose catabolism. Respiration G LY Glucose Fermentation C O LY NADH ATP S I S 2 Pyruvic acid NADH ATP Pyruvic acid (or derivative) Acetyl-CoA Formation of fermentation end-products FADH 2 NADH KREBS CYCLE e ATP ADP Electrons ATP Final electron acceptor Figure 5.12

19 Glycolysis Occurs in cytoplasm of most cells Involves splitting of a six-carbon glucose into two three-carbon sugar molecules Substrate-level phosphorylation direct transfer of phosphate between two substrates Net gain of two ATP molecules, two molecules of NADH, and precursor metabolite pyruvic acid

20 Cellular Respiration Resultant pyruvic acid completely oxidized to produce ATP by series of redox reactions Three stages of cellular respiration 1. Glycolysis 2. Krebs cycle (TCA Cycle) 3. Final series of redox reaction (electron transport chain)

21 The Nobel Prize in Physiology or Medicine 1953 Hans Krebs, Fritz Lipmann

22 The Krebs cycle Great amount of energy remains in bonds of acetyl-coa Transfers much of this energy to coenzymes NAD + and FAD Occurs in cytosol of prokaryotes and in matrix of mitochondria in eukaryotes

23 Figure 5.16 The Krebs cycle

24 The Krebs cycle Results in Two molecules of ATP Two molecules of FADH 2 Six molecules of NADH Four molecules of CO 2

25 Electron transport Most significant production of ATP occurs from series of redox reactions known as an electron transport chain (ETC) Series of carrier molecules that pass electrons from one to another to final electron acceptor Energy from electrons used to pump protons (H + ) across the membrane, establishing a proton gradient Located in cristae of eukaryotes and in cytoplasmic membrane of prokaryotes

26 Aerobic respiration Series or enzyme-catalyzed reactions in which electrons are transferred from fuel molecules (glucose) to oxygen as a final electron acceptor Glycolysis glucose (6C) is oxidized and split into 2 molecules of pyruvic acid (3C), NADH is generated TCA processes pyruvic acid and generates 3 CO 2 molecules, NADH and FADH 2 are generated Electron transport chain accepts electrons from NADH and FADH; generates energy through sequential redox reactions called oxidative phosphorylation

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28 Cellular Respiration: Electron transport Aerobic respiration: oxygen serves as final electron acceptor Anaerobic respiration: molecule other than oxygen serves as final electron acceptor These are Nitrates, Sulphates, Carbonates

29 Chemiosmosis Use of electrochemical gradients to generate ATP Cells use energy released in redox reactions of ETC to create proton gradient Protons flow down electrochemical gradient through ATP synthases that phosphorylate ADP to ATP Called oxidative phosphorylation because proton gradient is created by oxidation of components of ETC Total of ~34 ATP molecules formed from one molecule of glucose

30 An electron transport chain Respiration Fermentation e NAD + Path of electrons Reduced NADH FMN Oxidized ATP FADH 2 Oxidized FAD FeS Reduced ATP 2 H + Reduced CoQ Oxidized Oxidized Cyt Reduced 2 H + Reduced Cyt Oxidized Oxidized Cyt ATP e 2 H + Reduced 2 H + Final electron acceptor Figure 5.17

31 Sometimes cells cannot completely oxidize glucose by cellular respiration Fermentation Cells require constant source of NAD + Fermentation pathways provide cells with alternate source of NAD + Fermentation involves only Glycolysis and not Kreb s cycle Figure 5.21

32 Representative fermentation products and the organisms that produce them. Figure 5.22

33 Fermentation pathways Homolactic fermentation: Produces 2 molecules of lactic acid Ethanolic fermentation: Produces 2 molecules of ethanol and two CO 2 Heterolactic fermentation: Produces 1 molecule of lactic acid, 1 ethanol, and 1 CO 2 Mixed-acid fermentation: Produces acetate, formate, lactate, and succinate, as well as ethanol, H 2, and CO 2

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35 Other Catabolic Pathways Lipids and proteins contain energy in their chemical bonds Can be converted into precursor metabolites Serve as substrates in glycolysis and the Krebs cycle

36 Photosynthesis: Earth s lifeline Many organisms synthesize their own organic molecules from inorganic carbon dioxide Most of these organisms capture light energy and use it to synthesize carbohydrates from CO 2 and H 2 O by a process called photosynthesis light 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2

37 Chlorophylls Embedded in cellular membranes called thylakoids In prokaryotes invagination of cytoplasmic membrane In eukaryotes found in inner membrane of chloroplasts Stacks of thylakoids called grana Stroma is space between outer membrane of grana and thylakoid membrane

38 Occurs in 2 stages: Photosynthesis Light-dependent reactions depend on light energy Light-independent reactions synthesize glucose from carbon dioxide and water

39 Other Anabolic Pathways Anabolic reactions are synthesis reactions requiring energy and a source of precursor metabolites Energy derived from ATP from catabolic reactions Many anabolic pathways are the reverse of catabolic pathways Reactions that can proceed in either direction are amphibolic

40 Application of fermentation in diagnostic microbiology To quickly identify the microbe causing a disease and prescribe an effective antibiotic, hospitals use rapid and inexpensive biochemical tests. Carbohydrate fermentation test MacConkey agar

41 Metabolism PLAY MicroFlix TM : Metabolism

42 Integration and Regulation of Metabolic Function Cells synthesize or degrade, channel and transport proteins Cells often synthesize enzymes only when substrate is available Cells catabolize the more energy-efficient choice if two energy sources are available Cells synthesize metabolites they need, cease synthesis if metabolite is available

43 Integration and Regulation of Metabolic Function Eukaryotic cells isolate enzymes of different metabolic pathways within membrane-bounded organelles Cells use allosteric sites on enzymes to control activity of enzymes Feedback inhibition slows/stops anabolic pathways when product is in abundance Cells regulate amphibolic pathways by requiring different coenzymes for each pathway

44 Two types of regulatory mechanisms Control of gene expression Cells control amount and timing of protein (enzyme) production Control of metabolic expression Cells control activity of proteins (enzymes) once produced

45 Metabolism: The Big Picture PLAY Metabolism: The Big Picture