Foundations in Microbiology Seventh Edition

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Lecture PowerPoint to accompany Foundations in Microbiology Seventh Edition Talaro Chapter 8 To run the animations you must be in Slideshow View.

1 Lecture PowerPoint to accompany Foundations in Microbiology Seventh Edition Talaro Chapter 8 To run the animations you must be in Slideshow View. Use the buttons on the animation to play, pause, and turn audio/text on or off. Please Note: Once you have used any of the animation functions (such as Play or Pause), you must first click in the white background before you can advance to the next slide. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2 8.1 The Metabolism of Microbes Metabolism all chemical and physical workings of a cell Two types of chemical reactions: Catabolism degradative; breaks the bonds of larger molecules forming smaller molecules; releases energy Anabolism biosynthesis; process that forms larger macromolecules from smaller molecules; requires energy input 2

3 Figure 8.1 3

4 Enzymes Enzymes are biological catalysts that increase the rate of a chemical reaction by lowering the energy of activation The energy of activation is the resistance to a 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 4

5 5

6 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 6

7 Figure 8.2 Conjugated enzyme structure 7

8 8

9 9

10 Apoenzymes: Specificity and the Active Site Exhibits primary, secondary, tertiary, and some, quaternary structure Site for substrate binding is active site, or catalytic site 10

11 Figure

12 Apoenzymes: Specificity and the Active Site A temporary enzyme-substrate union occurs when substrate moves into active site induced fit Appropriate reaction occurs; product is formed and released 12

13 Figure

14 Figure 8.5 Carrier functions of coenzymes 14

15 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 Most enzymes are endoenzymes 15

16 Figure 8.6 Types of enzymes 16

17 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 17

18 Figure 8.7 Constitutive and regulated enzymes 18

19 Examples of Enzyme-catalyzed 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 Release ATP Requires the input of water to break bonds 19

20 Figure 8.8 Examples of Enzyme-catalyzed synthesis and hydrolysis reactions 20

21 Sensitivity of Enzymes to Their Environment Activity of an enzyme is influenced by cell s environment Enzymes operate under temperature, ph, and osmotic pressure of organism s habitat When enzymes are subjected to changes in organism s habitat they become unstable Labile: chemically unstable enzymes Denaturation: weak bonds that maintain the shape of the apoenzyme are broken 21

22 Role of Microbial Enzymes in Disease Protection from host defenses Promote pathogen replication Virulence factors or toxins S. pyogenes - streptokinase that digests blood clots aiding in wound invasion Penicillinase- inactivates penicillin 22

23 Metabolic Pathways Usually multistep; Enzymes play a major role in regulation Patterns Linear Cyclic Branched 23

24 Regulation of Enzymatic Activity and Metabolic Pathways 24

25 Direct Controls on the Actions of Enzymes 1. Competitive inhibition substance that resembles normal substrate competes with substrate for active site 2. Noncompetitive inhibition enzymes are regulated by the binding of molecules other than the substrate on the active site Enzyme repression inhibits at the genetic level by controlling synthesis of key enzymes Enzyme induction enzymes are made only when suitable substrates are present 25

26 Figure 8.10 Regulation of enzyme action 26

27 Figure 8.11 Enzyme repression 27

28 28

29 8.2 The Pursuit and Utilization of Energy Energy: the capacity to do work or to cause change Forms of energy include Thermal (heat) Radiant (visible light) Electrical (flow of electrons) Mechanical (physical change in position) Atomic (reactions in nucleus of atom) Chemical (bonds of molecules) 29

30 Cell Energetics Main source of energy- sun 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. The energy of these molecules is used in endergonic cell reactions. 30

31 Cell Energetics Exergonic Enzyme X + Y Z + Energy Endergonic Energy + Enzyme A + B C 31

32 Biological Oxidation and Reduction Many compounds readily participate in redox reactions Redox reactions always occur in pairs There is an electron donor and electron acceptor which constitute a redox pair Process salvages electrons and their energy Released energy can be captured to phosphorylate ADP or another compound 32

33 Fig. 9-UN1 The Principle of Redox becomes oxidized (loses electron) becomes reduced (gains electron) Charge on Cl is reduced from 0 to -1

34 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 34

35 35

36 Adenosine Triphosphate: ATP Metabolic currency 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 36

37 Figure 8.14 Structure of ATP 37

38 Figure 8.15 Phosphorylation of glucose by ATP 38

39 Formation of ATP ATP can be formed by three different mechanisms: 1. Substrate-level phosphorylation transfer of phosphate group from a phosphorylated compound (substrate) directly to ADP 2. Oxidative phosphorylation series of redox reactions occurring during respiratory pathway 3. Photophosphorylation ATP is formed utilizing the energy of sunlight 39

40 Figure 8.16 Formation of ATP by substrate-level phosphorylation 40

41 8.3 Pathways of Bioenergetics Bioenergetics study of the mechanisms of cellular energy release 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 41

42 Major Interconnections of the Pathways in Aerobic Respiration 42

43 Metabolic Strategies Nutrient processing is varied, yet in many cases is based on three catabolic pathways that convert glucose to CO 2 and gives off energy Aerobic respiration consumes organic molecules and O 2 and yields ATP glycolysis, the Kreb s cycle, respiratory chain Anaerobic respiration similar to aerobic respiration but molecular oxygen is not final electron acceptor glycolysis, the TCA cycle, respiratory chain; Fermentation a partial degradation of sugars that occurs without O 2 glycolysis, organic compounds are the final electron acceptors 43

44 Figure

45 45

46 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 Electron transport chain accepts electrons from NADH and FADH; Generates energy through sequential redox reactions called oxidative phosphorylation 46

Fig. 9-6-3 Electrons carried via NADH Electrons carried via NADH and FADH 2 Glucose Glycolysis Pyruvate Citric acid cycle Oxidative phosphorylation:

47 Fig Electrons carried via NADH Electrons carried via NADH and FADH 2 Glucose Glycolysis Pyruvate Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis Cytosol Mitochondrion ATP Substrate-level phosphorylation ATP Substrate-level phosphorylation ATP Oxidative phosphorylation

48 Figure

49 49

50 Figure

51 Figure

52 52

53 Electron Transport and Oxidative Phosphorylation Final processing of electrons and hydrogen and the major generator of ATP Chain of redox carriers that receive electrons from reduced carriers (NADH and FADH 2 ) ETS shuttles electrons down the chain, energy is released and subsequently captured and used by ATP synthase complexes to produce ATP Oxidative phosphorylation 53

54 Figure

55 55

56 The Formation of ATP and Chemiosmosis Chemiosmosis as the electron transport carriers shuttle electrons, they actively pump hydrogen ions (protons) across the membrane setting up a gradient of hydrogen ions proton motive force Hydrogen ions diffuse back through the ATP synthase complex causing it to rotate, causing a 3- dimensional change resulting in the production of ATP 56

57 57

58 Chemical and Charge Gradient between the Outer and Inner Compartments 58

59 Figure 8.22b 59

60 Electron Transport and ATP Synthesis in Bacterial Cell Envelope 60

61 The Terminal Step Oxygen accepts 2 electrons from the ETS and then picks up 2 hydrogen ions from the solution to form a molecule of water. Oxygen is the final electron acceptor 2H + + 2e - + ½O 2 H 2 O 61

Fig. 9-17 CYTOSOL Electron shuttles span membrane 2 NADH or MITOCHONDRIO N 2 FADH 2 2 NADH 2 NADH 6 NADH 2 FADH 2 Glycolysis 2 Glucose Pyruvate 2 Acetyl CoA

62 Fig CYTOSOL Electron shuttles span membrane 2 NADH or MITOCHONDRIO N 2 FADH 2 2 NADH 2 NADH 6 NADH 2 FADH 2 Glycolysis 2 Glucose Pyruvate 2 Acetyl CoA Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis + 2 ATP + 2 ATP + about 32 or 34 ATP Maximum per glucose: About 36 or 38 ATP

63 63

64 Anaerobic Respiration Functions like aerobic respiration except it utilizes oxygen containing ions, rather than free oxygen, as the final electron acceptor Nitrate (NO 3 - ) and nitrite (NO 2 - ) Most obligate anaerobes use the H + generated during glycolysis and the Kreb s cycle to reduce some compound other than O 2 64

65 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, and other products by the action of various bacteria on pyruvic acid 65

Fig. 9-19 Glucose CYTOSOL No O 2 present: Fermentation Pyruvate Glycolysis O 2 present:

66 Fig Glucose CYTOSOL No O 2 present: Fermentation Pyruvate Glycolysis O 2 present: Aerobic cellular respiration Ethanol or lactate Acetyl CoA MITOCHONDRIO N Citric acid cycle

67 Figure 8.25 Products of pyruvate fermentation 67

68 8.4 Biosynthesis and the Crossing Pathways of Metabolism Many pathways of metabolism are bi-directional or amphibolic Catabolic pathways contain molecular intermediates (metabolites) that can be diverted into anabolic pathways 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 68

69 Figure 8.27 Reactions that produce and convert amino acids 69

70 Figure

71 8.5 Photosynthesis: The Earth s Lifeline The ultimate source of all the chemical energy in cells comes from the sun light 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 71

72 Figure 8.28 Overview of photosynthesis 72

73 Photosynthesis Occurs in 2 stages Light-dependent photons are absorbed by chlorophyll, carotenoid, and phycobilin pigments Water split by photolysis, releasing O 2 gas and provide electrons to drive photophosphorylation Released light energy used to synthesize ATP and NADPH Light-independent reaction dark reactions Calvin cycle uses ATP to fix CO 2 to ribulose-1,5- bisphosphate and convert it to glucose 73

74 74

75 Figure

76 Figure 8.29c 76

77 Figure

Foundations in Microbiology Seventh Edition

Lecture PowerPoint to accompany Foundations in Microbiology Seventh Edition Talaro Chapter 8 An Introduction to Microbial Metabolism Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction