Ch5-Microbial Metabolism

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Ch5-Microbial Metabolism

• Metabolism The sum of the chemical reactions in
  an organism
• Catabolism Provides energy and building blocks
  for anabolism.
• Anabolism Uses energy and building blocks to
  build large molecules

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Role of ATP in Coupling Reactions
The energy for chemical reactions is stored in
ATP.
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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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Energy

• 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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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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Components of a Holoenzyme
The Mechanism of Enzymatic Action
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Enzyme Classification

• Oxidoreductase Oxidation-reduction reactions
• Transferase Transfer functional groups
• Hydrolase Hydrolysis
• Lyase Removal of atoms without hydrolysis
• Isomerase Rearrangement of atoms
• Ligase Joining of molecules, uses ATP

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Factors Influencing Enzyme Activity

• Temperature
• At high temperatures, enzymes undergo
  denaturation and lose their catalytic properties
  at low temperatures, the reaction rate decreases.
• pH
• optimum pH is the pH at which enzymatic activity
  is maximal
• Substrate concentration
• Enzymatic activity increases as substrate
  concentration increases until the enzymes are
  saturated.
• Inhibitors
• compete with the normal substrate for the active
  site of the enzyme decrease the enzymes
  ability to combine with the normal substrate.

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Enzyme Inhibitors Competitive Inhibition
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Enzyme Inhibitors Noncompetitive Inhibition
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Enzyme Inhibitors Feedback Inhibition

• Feedback inhibition occurs when the end-product
  of a metabolic pathway inhibits an enzymes
  activity near the start of the pathway.

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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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Oxidation-Reduction Reactions

• In biological systems, the electrons are often
  associated with hydrogen atoms. Biological
  oxidations are often dehydrogenations.

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The Generation of ATP

• ATP is generated by the phosphorylation of ADP

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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

Substrate-Level Phosphorylation

• Energy from the transfer of a high-energy PO4 to
  ADP generates ATP

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Photophosphorylation

• In plants, algae, photosynthetic bacteria
• 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

• Most of a cells energy is produced from the
  oxidation of carbohydrates.
• The breakdown of carbohydrates to release energy
• Glycolysis

• The two major types of glucose catabolism are
  respiration, in which glucose is completely
  broken down, and fermentation, in which it is
  partially broken down.

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Glycolysis

• Glucose 2 ATP 2 ADP 2 PO4 2 NAD ? 2
  pyruvic acid 4 ATP 2 NADH 2H
• Two ATP (NET) and two NADH molecules are produced
  from one glucose molecule.

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Alternatives to Glycolysis

• Pentose phosphate pathway
• Creates pentoses (5 carbon sugars) and NADPH
• Operates with glycolysis
• 1 glucose creates 1 ATP 12 NADPH molecules
• Entner-Doudoroff pathway
• Produces 1 ATP 2 NADPH molecules
• 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

• Pyruvic acid (from glycolysis) is oxidized and
  decarboyxlated

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The Krebs Cycle

• Oxidation of acetyl CoA produces NADH and FADH2

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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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Overview of Respiration and Fermentation
Figure 5.11
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The Chemiosmotic Mechanism of ATP Generation

• In eukaryotes, electron carriers are located in
  the inner mitochondrial membrane in prokaryotes,
  electron carriers are in the plasma membrane.
• Protons being pumped across the membrane generate
  a proton motive force as electrons move through a
  series of acceptors or carriers.

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Chemiosmotic Generation of ATP
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An Overview of Chemiosmosis
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A Summary of Respiration

• Aerobic respiration The final electron acceptor
  in the electron transport chain is molecular
  oxygen (O2). (in aerobic prokaryotes--38ATP
  produced from each glucose)
• 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 cycles operates
  under anaerobic conditions.

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Respiration
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Anaerobic Respiration
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Carbohydrate Catabolism
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Carbohydrate Catabolism

• Energy produced from complete oxidation of one
  glucose using aerobic respiration

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Carbohydrate Catabolism

• ATP produced from complete oxidation of one
  glucose using aerobic respiration

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Carbohydrate Catabolism

• 36 ATPs are produced in eukaryotes

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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

Glucose fermentation is one test used to
differentiate between Escherichia coli and
Pseudomonas aeruginosa. Pseudomonas does NOT
ferment glucose E. coli does.
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An Overview of Fermentation
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End-Products of Fermentation
Figure 5.18b
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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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Types of Fermentation
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A Fermentation Test
Fermentation tests are used to determine whether
an organism can ferment a carbohydrate to produce
acid and gas.
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Types of Fermentation
Table 5.4
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Types of Fermentation
Table 5.4
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Lipid Catabolism

• Lipases hydrolyze lipids into glycerol and fatty
  acids.
• Catabolic products can be further broken down in
  glycolysis and the Krebs cycle.

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Catabolism of Organic Food Molecules
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Protein Catabolism

• Before amino acids can be catabolized, they must
  be converted to various substances that enter the
  Krebs cycle.

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Sulfur Catabolism
Desulfurylation
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Urea Catabolism
Urease
NH3 CO2
Urea
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Biochemical Tests

• Used to identify bacteria.

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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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Photosynthesis

• Oxygenic
• Anoxygenic

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Cyclic Photophosphorylation

• Chlorophyll a is used by green plants, algae, and
  cyanobacteria it is found in thylakoid
  membranes.
• ATP is produced by chemiosmosis the electrons
  return to the chlorophyll.

ANIMATION Photosynthesis Light Reaction Cyclic
Photophosphorylation
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Noncyclic Photophosphorylation

• The electrons are used to reduce NADP. The
  electrons from H2O or H2S replace those lost from
  chlorophyll.

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Calvin-Benson Cycle
CO2 is used to synthesize sugars in the
Calvin-Benson cycle.
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Photosynthesis Compared
Table 5.6
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Chemotrophs

• Use energy from chemicals
• Chemoautotroph, Thiobacillus ferrooxidans
• Energy used in the Calvin-Benson cycle to fix CO2

2Fe2
NAD
ETC
2Fe3
NADH
ADP P
ATP
2 H
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Phototrophs

• Use light energy
• Photoautotrophs use energy in the Calvin-Benson
  cycle to fix CO2
• Photoheterotrophs use energy

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A Nutritional Classification of Organisms
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A Nutritional Classification of Organisms
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Metabolic Diversity among Organisms
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Polysaccharide Biosynthesis

• Glycogen is formed from ADPG.
• UDPNAc is the starting material for the
  biosynthesis of peptidoglycan.

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Lipid Biosynthesis

• Lipids are synthesized from fatty acids and
  glycerol.
• Glycerol is derived from dihydroxyacetone
  phosphate, and fatty acids are built from acetyl
  CoA.

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Pathways of Amino Acid Biosynthesis

• Amino acids are required for protein
  biosynthesis.
• All amino acids can be synthesized either
  directly or indirectly from intermediates of
  carbohydrate metabolism, particularly from the
  Krebs cycle.

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Amphibolic Pathways
Metabolic pathways that have both catabolic and
anabolic functions