05_lecturebio350
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Bio 350TRANSCRIPT
Copyright © 2013 Pearson Education, Inc.Lectures prepared by Christine L. Case
Chapter 5
Microbial Metabolism
© 2013 Pearson Education, Inc. Lectures prepared by Christine L. Case
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Catabolic and Anabolic Reactions
Metabolism: the sum of the chemical reactions in an organism
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Catabolic and Anabolic Reactions
Catabolism: provides energy and building blocks for anabolism
Anabolism: uses energy and building blocks to build large molecules
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Figure 5.1 The role of ATP in coupling anabolic and catabolic reactions.
Catabolism releases energyby oxidation of molecules
Energy isstored inmoleculesof ATP
Anabolism uses energy tosynthesize macromoleculesthat make up the cell
Energy isreleased byhydrolysisof ATP
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ANIMATION Metabolism: Overview
Catabolic and Anabolic Reactions
A metabolic pathway is a sequence of enzymatically catalyzed chemical reactions in a cell
Metabolic pathways are determined by enzymes Enzymes are encoded by genes
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Collision Theory
The collision theory states that chemical reactions can occur when atoms, ions, and molecules collide
Activation energy is needed to disrupt electronic configurations
Reaction rate is the frequency of collisions with enough energy to bring about a reaction
Reaction rate can be increased by enzymes or by increasing temperature or pressure
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Figure 5.2 Energy requirements of a chemical reaction.
Reactionwithout enzyme
Reactionwith enzyme
Reactant
Initial energy level
Final energy level
Products
Activationenergywithout enzyme
Activationenergywithenzyme
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Enzyme Components
Biological catalysts Specific for a chemical reaction; not used up in that
reaction
Apoenzyme: protein Cofactor: nonprotein component
Coenzyme: organic cofactor
Holoenzyme: apoenzyme plus cofactor
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Figure 5.3 Components of a holoenzyme.
Coenzyme Substrate
Apoenzyme (protein portion),
inactive
Cofactor(nonprotein portion),
activator
Holoenzyme(whole enzyme),
active
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Important Coenzymes
NAD+
NADP+
FAD Coenzyme A
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Figure 5.4a The mechanism of enzymatic action.
Substrate Active site
Enzyme–substrate
Products
Enzymecomplex
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Figure 5.4b The mechanism of enzymatic action.
Substrate
EnzymeSubstrate
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Factors Influencing Enzyme Activity
Temperature pH Substrate concentration Inhibitors
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Temperature and pH denature proteins
Factors Influencing Enzyme Activity
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Figure 5.6 Denaturation of a protein.
Active (functional) protein Denatured protein
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Figure 5.5a Factors that influence enzymatic activity, plotted for a hypothetical enzyme.
(a) Temperature. The enzymatic activity (rate of reaction catalyzed by the enzyme) increases with increasing temperature until the enzyme, a protein, is denatured by heat and inactivated. At this point, the reaction rate falls steeply.
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Figure 5.5b Factors that influence enzymatic activity, plotted for a hypothetical enzyme.
(b) pH. The enzyme illustrated is most active at about pH 5.0.
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Figure 5.5c Factors that influence enzymatic activity, plotted for a hypothetical enzyme.
(c) Substrate concentration. With increasing concentration of substrate molecules, the rate of reaction increases until the active sites on all the enzyme molecules are filled, at which point the maximum rate of reaction is reached.
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Enzyme Inhibitors: Competitive Inhibition
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Figure 5.7ab Enzyme inhibitors.
Normal Binding of Substrate Action of Enzyme Inhibitors
Substrate
Active site
Enzyme
Competitiveinhibitor
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Enzyme Inhibitors: Competitive Inhibition
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Enzyme Inhibitors: Noncompetitive Inhibition
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Figure 5.7ac Enzyme inhibitors.
Normal Binding of Substrate
Substrate
Active site
Enzyme
Action of Enzyme Inhibitors
Noncompetitiveinhibitor Allosteric
site
Alteredactive site
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Enzyme Inhibitors: Feedback Inhibition
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Figure 5.8 Feedback inhibition.
Substrate
PathwayOperates
Intermediate A
Intermediate B
End-product
Enzyme 1
Allosteric site
Enzyme 2
Bound end-product
Pathway Shuts Down
Fe
ed
ba
ck
In
hib
itio
n
Enzyme 3
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Oxidation-Reduction Reactions
Oxidation: removal of electrons Reduction: gain of electrons Redox reaction: an oxidation reaction paired with
a reduction reaction
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Figure 5.9 Oxidation-reduction.
Reduction
A oxidized B reduced
Oxidation
A B
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ANIMATION Oxidation-Reduction Reactions
Oxidation-Reduction Reactions
In biological systems, the electrons are often associated with hydrogen atoms
Biological oxidations are often dehydrogenations
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Figure 5.10 Representative biological oxidation.
Reduction
Oxidation
H+
(proton)
Organic moleculethat includes twohydrogen atoms
(H)
NAD+ coenzyme(electron carrier)
Oxidized organic
molecule
NADH + H+ (proton)(reduced electron
carrier)
H
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ATP is generated by the phosphorylation of ADP
The Generation of ATP
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The Generation of ATP
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Energy from the transfer of a high-energy PO4– to
ADP generates ATP
Substrate-Level Phosphorylation
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Substrate-Level Phosphorylation
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Oxidative Phosphorylation
Energy released from transfer of electrons (oxidation) of one compound to another (reduction) is used to generate ATP in the electron transport chain
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Photophosphorylation
Light causes chlorophyll to give up electrons Energy released from transfer of electrons
(oxidation) of chlorophyll through a system of carrier molecules is used to generate ATP
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Carbohydrate Catabolism
The breakdown of carbohydrates to release energy Glycolysis Krebs cycle Electron transport chain
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Glycolysis
The oxidation of glucose to pyruvic acid produces ATP and NADH
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Figure 5.11 An Overview of Respiration and Fermentation.
1
3
2
The Krebs cycle produces some ATP by substrate-level phosphorylation, reduces the electron carriers NAD+ and FAD, and gives off CO2. Carriers from both glycolysis and the Krebs cycle donate electrons to the electron transport chain.
In the electron transportchain, the energy of theelectrons is used toproduce a great deal ofATP by oxidativephosphorylation.
Glycolysis produces ATP and reduces NAD+ to NADH while oxidizing glucose to pyruvic acid. In respiration, the pyruvic acid is converted to the first reactant in the Krebs cycle, acetyl CoA.
In fermentation, the pyruvic acid and the electrons carried by NADH from glycolysis are incorporated into fermentation end-products.
brewer’s yeast
NADH
NADH
NADH
FADH2
NADH & FADH2
Glycolysis
Glucose
Pyruvic acid
Pyruvic acid(or derivative)
Formation offermentationend-products
ATP
ATP
ATPCO2
O2
Electrons
Acetyl CoA
Electrontransportchain andchemiosmosis
respiration fermentation
H2O
Kreb’scycle
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Preparatory Stage of Glycolysis
2 ATP are used Glucose is split to form 2 glucose-3-phosphate
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2 glucose-3-phosphate are oxidized to 2 pyruvic acid 4 ATP are produced 2 NADH are produced
Energy-Conserving Stage of Glycolysis
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Glycolysis
Glucose + 2 ATP + 2 ADP + 2 PO4– + 2 NAD+ 2
pyruvic acid + 4 ATP + 2 NADH + 2H+
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Alternatives to Glycolysis
Pentose phosphate pathway Uses pentoses and NADPH Operates with glycolysis
Entner-Doudoroff pathway Produces NADPH and ATP Does not involve glycolysis Pseudomonas, Rhizobium, Agrobacterium
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Cellular Respiration
Oxidation of molecules liberates electrons for an electron transport chain
ATP is generated by oxidative phosphorylation
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Pyruvic acid (from glycolysis) is oxidized and decarboxylated
Intermediate Step
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The Krebs Cycle
Oxidation of acetyl CoA produces NADH and FADH2
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ANIMATION Electron Transport Chain: Overview
The Electron Transport Chain
A series of carrier molecules that are, in turn, oxidized and reduced as electrons are passed down the chain
Energy released can be used to produce ATP by chemiosmosis
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Figure 5.14 An electron transport chain (system).
Flow of electrons
Energy
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Figure 5.11 An Overview of Respiration and Fermentation.
1
3
2
The Krebs cycle produces some ATP by substrate-level phosphorylation, reduces the electron carriers NAD+ and FAD, and gives off CO2. Carriers from both glycolysis and the Krebs cycle donate electrons to the electron transport chain.
In the electron transportchain, the energy of theelectrons is used toproduce a great deal ofATP by oxidativephosphorylation.
Glycolysis produces ATP and reduces NAD+ to NADH while oxidizing glucose to pyruvic acid. In respiration, the pyruvic acid is converted to the first reactant in the Krebs cycle, acetyl CoA.
In fermentation, the pyruvic acid and the electrons carried by NADH from glycolysis are incorporated into fermentation end-products.
brewer’s yeast
NADH
NADH
NADH
FADH2
NADH & FADH2
Glycolysis
Glucose
Pyruvic acid
Pyruvic acid(or derivative)
Formation offermentationend-products
ATP
ATP
ATPCO2
O2
Electrons
Acetyl CoA
Electrontransportchain andchemiosmosis
respiration fermentation
H2O
Kreb’scycle
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Cytoplasm
Bacterium Mitochondrion
Intermembrane space
Mitochondrial matrix
Cellwall
Periplasmic space
Plasma membrane
Outer membrane
Inner membrane
Periplasmic space of prokaryote or intermembrane space of eukaryote
Prokaryoticplasmamembraneor eukaryoticinner mitochondrial membrane
Cytoplasm ofprokaryote ormitochondrialmatrix ofeukaryote
Figure 5.16 Electron transport and the chemiosmotic generation of ATP.
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Figure 5.15 Chemiosmosis.
High H+ concentration
Low H+ concentration
Membrane
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A Summary of Respiration
Aerobic respiration: the final electron acceptor in the electron transport chain is molecular oxygen (O2)
Anaerobic respiration: the final electron acceptor in the electron transport chain is NOT O2
Yields less energy than aerobic respiration because only part of the Krebs cycle operates under anaerobic conditions
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Respiration
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Pathway Eukaryote Prokaryote
Glycolysis Cytoplasm Cytoplasm
Intermediate step Cytoplasm Cytoplasm
Krebs cycle Mitochondrial matrix Cytoplasm
ETC Mitochondrial inner membrane Plasma membrane
Carbohydrate Catabolism
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Energy produced from complete oxidation of one glucose using aerobic respiration
Pathway ATP Produced NADH Produced
FADH2 Produced
Glycolysis 2 2 0
Intermediate step 0 2 0
Krebs cycle 2 6 2
Total 4 10 2
Carbohydrate Catabolism
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ATP produced from complete oxidation of one glucose using aerobic respiration
Pathway By Substrate-Level Phosphorylation
By Oxidative Phosphorylation
From NADH From FADH
Glycolysis 2 6 0
Intermediate step 0 6 0
Krebs cycle 2 18 4
Total 4 30 4
Carbohydrate Catabolism
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36 ATPs are produced in eukaryotes
Pathway By Substrate-Level Phosphorylation
By Oxidative Phosphorylation
From NADH From FADH
Glycolysis 2 6 0
Intermediate step 0 6 0
Krebs cycle 2 18 4
Total 4 30 4
Carbohydrate Catabolism
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Fermentation
Any spoilage of food by microorganisms (general use)
Any process that produces alcoholic beverages or acidic dairy products (general use)
Any large-scale microbial process occurring with or without air (common definition used in industry)
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Fermentation
Scientific definition: Releases energy from oxidation of organic molecules Does not require oxygen Does not use the Krebs cycle or ETC Uses an organic molecule as the final electron acceptor
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Figure 5.18a Fermentation.
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Figure 5.18b Fermentation.
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Fermentation
Alcohol fermentation: produces ethanol + CO2
Lactic acid fermentation: produces lactic acid Homolactic fermentation: produces lactic acid only Heterolactic fermentation: produces lactic acid and other
compounds
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Figure 5.19 Types of fermentation.
(a) Lactic acid fermentation
(b) Alcohol fermentation
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Figure 5.23 A fermentation test.
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Figure 5.21 Catabolism of various organic food molecules.
Electrontransportchain andchemiosmosis
Krebscycle
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Protein Amino acidsExtracellular proteases
Krebs cycle
Deamination, decarboxylation, dehydrogenation, desulfurization
Organic acid
Protein Catabolism
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Figure 5.22 Detecting amino acid catabolizing enzymes in the lab.
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Urease NH3 + CO2Urea
Protein Catabolism
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Clinical Focus: Human Tuberculosis – Dallas, Texas
Figure B The urease test.
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Used to identify bacteria
Biochemical Tests
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Clinical Focus: Human Tuberculosis – Dallas, Texas
Figure A An identification scheme for selected species of slow-growing mycobacteria.
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ANIMATION Photosynthesis: Overview
Photosynthesis
Photo: conversion of light energy into chemical energy (ATP) Light-dependent (light) reactions
Synthesis: Carbon fixation: fixing carbon into organic molecules Light-independent (dark) reaction: Calvin-Benson cycle
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Figure 4.15 Chromatophores.
Chromatophores
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Cyclic Photophosphorylation
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Figure 5.25a Photophosphorylation.
LightExcitedelectrons
Electrontransportchain
Electron carrier
In Photosystem I(a) Cyclic photophosphorylation
Energy forproductionof ATP
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Noncyclic Photophosphorylation
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Figure 5.25b Photophosphorylation.
Excitedelectrons
Excitedelectrons
(b) Noncyclic photophosphorylation
Electrontransportchain Energy for
productionof ATP
Light
Light
In Photosystem II
In Photosystem I
H+ + H+
12
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Calvin-Benson Cycle
CO2 is used to synthesize sugars in the Calvin-Benson Cycle.
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Use energy from chemicals Chemoheterotroph
Energy is used in anabolism
Glucose
Pyruvic acid
NAD+
NADH
ETC
ADP + P ATP
Chemotrophs
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Chlorophyll
Chlorophylloxidized
ETC
ADP + P ATP
Phototrophs
Use light energy
Photoautotrophs use energy in the Calvin-Benson cycle to fix CO2
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Figure 5.27 Requirements of ATP production.
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Figure 5.29 The biosynthesis of polysaccharides.
Glycogen(in bacteria)
Glycogen(in animals)
Peptidoglycan(in bacteria)
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Figure 5.30 The biosynthesis of simple lipids.
Krebscycle
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Figure 5.31a The biosynthesis of amino acids.
Krebscycle
Amination or transamination
Amino acid biosynthesis
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Figure 5.32 The biosynthesis of purine and pyrimidine nucleotides.
Krebscycle