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Chapter 5: Microbial Metabolism

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Title: Chapter 5: Microbial Metabolism


1
Chapter 5Microbial Metabolism
2
Microbial Metabolism
  • Metabolism the sum of the chemical reactions in
    an organism
  • Catabolism energy-releasing processes
  • Breakdown of complex organic compounds
  • Exergonic reactions
  • Coupled to ATP synthesis
  • Anabolism energy-requiring processes
  • Building of complex organic compounds from
    simpler ones
  • Endergonic reactions
  • Coupled to ATP hydrolysis/breakdown

3
Catabolism provides the building blocks and
energy for anabolism
ATP
Catabolic Reactions (ATP energy extracted and
stored)
Anabolic Reactions (ATP energy utilized)
ADP Pi
4
Microbial MetabolismMetabolic Pathways
  • Metabolic pathway a sequence of enzymatically
    catalyzed chemical reactions in a cell
  • Metabolic pathways are determined by enzymes
  • Enzymes are encoded by genes

5
Metabolic Reactions
  • Chemical reactions occur when bonds are formed or
    broken
  • Chemical reactions may occur when atoms, ions,
    and molecules collide
  • Activation energy minimum amount of energy
    needed to disrupt electronic configurations so
    that electrons can be rearranged

6
Activation Energy
Figure 5.2
7
Metabolic Reactions
  • Reaction rate the frequency of collisions with
    enough energy to cause a reaction
  • Can be increased by
  • Increasing temperature (velocity, collision freq,
    energy of molecules)
  • Increasing pressure ( distance between
    molecules)
  • Increasing reactant concentration
  • Enzymes

8
Enzymes
  • Enzymes are proteins
  • Names usually end in -ase
  • Some enzymes require cofactors
  • Cofactor Nonprotein component of active enzyme
  • Examples NAD, FAD

9
Enzymes
  • Biological catalysts speed up chemical reactions
  • Specific for its designated chemical reaction
  • Specificity conferred by the 3D shape of the
    enzyme (especially its active site) and substrate
  • Induced fit of the substrate into the active
    site pocket
  • Not changed or used up in that reaction

E-S complex
10
EnzymesMechanism of action
  • Orient the substrate(s) into a position that
    increases the probability of a favorable
    collision (a reaction)
  • E-S complex transient binding enables more
    effective collisions and lowers the Ea of a
    reaction
  • Substrate binds to the enzymes active site
  • Can increase the reaction rate up to 10 bil times
    higher
  • Turnover number 1-10,000 molecules per second

Figure 5.4
(Enzyme is unchanged)
11
Activation Energy
  • Enzymes increase the rate of a reaction by
    decreasing the activation energy

Figure 5.2
12
Enzyme Activity
  • Factors influencing enzyme activity
  • Temperature
  • pH
  • Substrate concentration
  • Inhibitors (competitive and noncompetitive)

13
Factors Influencing Enzyme ActivityDenaturation
  • Enzymes can be denatured by temperature and pH
    changes
  • Denaturation loss of 3-D conformation
  • Denaturation due to breakage of H-bonds and ionic
    bonds
  • Disruption of active site?loss of enzymatic
    function

(Nonfunctional)
Figure 5.6
14
Factors Influencing Enzyme ActivityTemperature
  • Temperature

Optimal temperature
Figure 5.5a
15
Factors Influencing Enzyme ActivitypH
  • pH

Optimal pH
Figure 5.5b
16
Factors Influencing Enzyme ActivitySubstrate
Concentration
  • Substrate concentration

Figure 5.5c
17
Factors Influencing Enzyme ActivityInhibitors
  • Competitive inhibition
  • Inhibitor blocks substrate access to active site
  • Reversible or irreversible

Figure 5.7a, b
18
Factors Influencing Enzyme ActivityCompetitive
Inhibitors
Enzyme substrate
(Sulfa drug)
19
Factors Influencing Enzyme ActivityNoncompetitiv
e Inhibitors
  • Noncompetitive inhibition the inhibitor does
    not compete with the substrate for the active
    site
  • Inhibitor interacts with another area of enzyme
    (allosteric site)
  • Causes a change in the shape of enzymes active
    site
  • Reversible or irreversible

Figure 5.7a, c
20
Summary of Energy Production Mechanisms
Figure 5.26
21
Metabolic reactionsOxidation-Reduction
  • Oxidation the loss of electrons
  • Reduction the gain of electrons
  • Redox reaction an oxidation reaction paired with
    a reduction reaction

Figure 5.9
22
Metabolic ReactionsEnergy Production
  • Most of the energy released in catabolic
    reactions is trapped in the cell by the formation
    of ATP
  • ATP energy currency (readily usable energy)
  • Unstable (high-energy) bonds ()
  • Generated by the phosphorylation of ADP
  • Phosphorylationaddition of a phosphate group

23
The Generation of ATP
  • Oxidative phosphorylation Generation of ATP by
    chemiosmosis
  • Occurs as a result of the electron transport
    chain during aerobic and anaerobic cellular
    respiration
  • Also substrate-level phosphorylation and
    photophosphorylation (photosynthesis)

24
Carbohydrate CatabolismNAD and FAD Cofactors
  • NAD and FAD are electron carriers
  • Electrons have energy-generation potential
  • Electrons are sequentially plucked off of glucose
    and delivered to the ETC (or another final
    electron acceptor)
  • During redox reactions, protons (H) usually
    travel with electrons
  • NAD 2e- NADH H
  • FAD 2e- FADH2

2H
2H
(Reduced cofactors)
(Oxidized cofactors)
25
Carbohydrate Catabolism
  • The breakdown of carbohydrates to release energy
  • Stepwise oxidation of glucose

Fermentation -Glycolysis (or
alternatives) -Fermentation
Cellular Respiration -Glycolysis -Krebs
cycle -ETC/ chemiosmosis
26
Glycolysis
  • The oxidation of glucose to pyruvic acid,
    produces ATP and NADH
  • i.e. the splitting of 6C glucose into two 3C
    pyruvic acids

NAD
ATP
NADH
2
2
27
Cellular Respiration
  • Sequential oxidation of molecules frees electrons
    which are delivered to the electron transport
    chain
  • Electrons are carried by NADH and FADH2
  • Final electron acceptor is an inorganic molecule
    at the end of the ETC
  • O2 (aerobic)
  • NO3- or SO42- (anaerobic)
  • Most ATP is generated by oxidative
    phosphorylation (ETC/Chemiosmosis)

28
Cellular RespirationKrebs Cycle
  • Oxidation of acetyl CoA produces 3 NADH and 1
    FADH2
  • Decarboxylations release of CO2 as waste
  • 6 CO2 per glucose
  • Oxidation-reduction reactions
  • NAD is reduced to NADH
  • FAD is reduced to FADH2
  • NADH and FADH2 contain most of the energy
    originally contained in glucose
  • Proceed to ETC

Figure 5.13.2
29
Cellular RespirationThe Electron Transport Chain
  • A series of electron transfer molecules that are
    sequentially reduced and oxidized as electrons
    are passed down the chain
  • Electrons are delivered here by NADH and FADH2
  • Electrons reach their final electron acceptor at
    the end of the ETC
  • Energy released is used to set up the proton
    gradient that drives chemiosmosis (ATP
    production)
  • Located in the plasma membrane (prokaryotes) or
    the inner mitochondrial membrane (eukaryotes)

30
Cellular RespirationThe Electron Transport Chain
Figure 5.14
  • Aerobic cellular respiration O2 (the final
    electron acceptor) becomes negatively charged and
    picks up protons from its surroundings to form H2O

31
Cellular RespirationChemiosmosis
  • Three members of the ETC, actively transport H
    across the membrane
  • Buildup of H on one side of the membrane
  • Electrochemical gradient
  • Protons travel down the electrochemical gradient
    through a specialized protein channel (ATP
    synthase)
  • Energy is released and used by ATP synthase to
    form ATP

Figure 5.15
32
Cellular RespirationChemiosmosis
Figure 5.16.2
33
Cellular RespirationSummary
  • Majority of ATP generation from glucose oxidation
    takes place at the ETC
  • ETC regenerates NAD and FAD
  • Can be used in the next round of glycolysis and
    Krebs cycle

34
Cellular Respiration
  • Aerobic respiration The final electron acceptor
    in the ETC is molecular oxygen (O2)
  • Anaerobic respiration The final electron
    acceptor in the ETC is an inorganic molecule
    other than O2
  • NO3-, SO42-, CO2 etc.
  • Yields less energy than aerobic respiration
    because only part of the Krebs cycle operations
    and ETC are used

35
Fermentation
  • Releases energy from (incomplete) 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
  • Produces small amounts of ATP
  • Most of the energy of the starting material is
    still contained in chemical bonds of the organic
    end-product
  • Regenerates NAD for next round of glycolysis
  • Glycolysis-only source of ATP generation

Figure 5.18
36
Fermentation
  • Fermentation end-products depend upon the
    microorganism, substrate, and enzymes
    present/active

Figure 5.18b
37
Fermentation
Bread rises
Food production Food spoilage
Alcoholic beverages
Figure 5.19
38
Lipid and Protein Catabolism
Extracellular proteases
39
Biochemical tests
  • Used to identify bacteria

Figure 10.8
40
Photosynthesis
  • Photo Conversion of light energy into chemical
    energy (ATP)
  • Light-dependent (light) reactions
  • Synthesis Fixing carbon into organic molecules
    (sugars)
  • Anabolism
  • Light-independent (dark) reaction, Calvin-Benson
    cycle
  • Electron donors photosynthetic pigment (i.e.
    chlorophyll)

41
Photosynthesis
  • Sun energy is captured by phototrophs and
    converted to chemical energy (ATP) used to build
    organic molecules (i.e. glucose)

Photosynthesis
Glucose
O2
CO2 H2O
Glycolysis Cellular Respiration
42
PhotosynthesisThe big picture
  • Synthesis of complex, reduced organic molecules
    (sugars) from simple inorganic substances (CO2)
  • Carbon fixation synthesis of sugars from carbon
    in CO2 gas
  • Electrons are incorporated into energy-rich
    sugars
  • Oxygenic (plants, algae, cyanobacteria) 6 CO2
    12 H2O Light energy ? C6H12O6 6 O2 6 H2O
  • Anoxygenic (purple sulfur green sulfur
    bacteria) CO2 2 H2S Light energy ? CH2O
    2 S H2O

43
Summary of Energy Production Mechanisms
Figure 5.26
44
Metabolic Diversity Among Organisms
  • Classifications based on energy and carbon
    sources of organisms
  • Principal energy source
  • Phototrophs light
  • Chemotrophs chemicals
  • Principal carbon source
  • Autotrophs CO2 (inorganic)
  • Heterotrophs organic compounds

45
Metabolic Diversity Among Organisms
Nutritional type Energy source Carbon source Example
Photoautotroph Light CO2 Oxygenic Cyanobacteria, plants Anoxygenic Green, purple bacteria
Photoheterotroph Light Organic compounds Green, purple nonsulfur bacteria
Chemoautotroph Chemical CO2 Iron-oxidizing bacteria
Chemoheterotroph Chemical Organic compounds Animals, protozoa, fungi, bacteria Fermentative bacteria
46
Metabolic Pathways of Energy Use
  • Glucose metabolism is considered efficient, but
    45 of energy from glucose is lost as heat!
  • Remaining energy is stored in the chemical bonds
    of ATP
  • Most ATP is used in the production of new
    cellular components (ANABOLISM!)

47
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