5-b
Microbial Metabolism
pp. 115-138; 144-148
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Chapter 5 Overview
• Metabolism
• Enzymes
• Common energy pathways used by
microbes
– Aerobic respiration
– Anaerobic respiration
– Fermentation
• Metabolic diversity among organisms
2
*View the Animation:
Metabolic Pathways (Overview)
* Log on to: www.microbiologyplace.com
3
Common Energy Pathways
Used by Microbes
– Fermentation
– Aerobic respiration
– Anaerobic respiration
These processes start with glycolysis
– Then, follow different subsequent pathways
4
Overview:
2
Glycolysis
Oxidation of
glucose to
pyruvate
Krebs cycle
Oxidation of
pyruvate to
CO2
ETS
Ox-redox
cascade
2
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Fig. 5.11
5
Overview: Respiration
• Long series of oxidation-reduction reactions
• It’s a ‘flow’ of electrons from
– Energy-rich glucose molecule
– To relatively energy-poor CO2 and H2O
molecules
• Coupled with energy-rich ATP production
Glycolysis  Krebs cycle  ETS
6
Cellular Respiration
2 types of respiration:
• Aerobic microbe
– Uses oxygen
– Final electron acceptor is O2
• Anaerobic microbe
– Does not use oxygen
– Final electron acceptor is an inorganic
molecule other than O2
7
Aerobic Respiration
Characteristics:
• High energy pathway
– 36-38 ATP produced per molecule of
carbohydrate
• The pathway occurs in the
– Cytoplasm, mitochondria (eukaryotic cells only)
– Using glycolysis, Krebs cycle, ETS
• Products include:
– CO2, H2O and 38 ATP
8
Electron Transport System:
(Example: Eukaryotic cells)
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• Electrons move along the chain
• Via oxidation-reduction reactions
• Energy is released at each step
Fig. 5.14
9
The ETS & Bacteria
• The ETS chains of bacteria are diverse
when compared with other bacteria and
eukaryotic cells
– If the bacteria are missing Cytochrome C
• They are oxidase negative
– If the bacteria that have Cytochrome C
• They are oxidase positive
See also Lab experiment 15
10
Summary
of aerobic
respiration:
Glucose is
broken down
to:
• CO2
• Water
• 38 ATP
Fig. 5.17
11
Anaerobic Respiration
Characteristics:
• There is no single common pathway
• The initial electron donor can be organic or
inorganic
• The final electron acceptor is an inorganic
compound other than O2
– Example ions: NO3-, SO42-, CO32-
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Example Ions: NO3-, SO42-, CO32Ion used as final
Reduced to form:
electron acceptor:
Nitrate: NO3Nitrite: NO2Nitrous Oxide: N2O
Pseudomonas, Bacillus
Nitrogen gas: N2
Sulfate: SO42Hydrogen sulfide: H2S
Desulfovibrio
Carbonate: CO32-
Methane: CH4
Other
See also Lab experiments 16, 21
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Characteristics (cont):
• The amount of ATP generated per
molecule substrate respired varies
– The ATP generated is never as much as in
aerobic respiration
– But, never as little as in fermentation!
• And, anaerobes tend to grow more
slowly
14
Fermentation
• Glucose is broken down to pyruvic acid
– Pyruvic acid can then be broken down via
respiration (glycolysis)
• Or, it can be converted to an organic
product in fermentation
– i.e., NAD+ and NADP+ are regenerated
– And, enter another round of glycolysis
15
Fig. 5.11
16
Fermentation
Characteristics:
• Releases energy from sugars or other
organic molecules
– Amino acids, organic acids, purines, pyrimidines
• Does not require oxygen
• Does not require Krebs, or ETS
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Fermentation
Characteristics cont:
• Uses an organic molecule as the final
electron acceptor
– Lactic acid, ethanol, propionic acid, acetic acid,
butyric acid, acetone, formic acid, etc.
• Produces small amounts of ATP
– Much of the energy remains in the chemical
bonds of the organic end products
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Principal products:
• Organic acids
• Alcohols
• Gases: CO2 and H2
• ATP
Most common substrate:
• Carbohydrates (e.g., glucose)
Pathway:
• Occurs in the cell cytoplasm
– NOT in the mitochondria
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End products depend on:
•
•
•
•
•
The particular microbe
The substrate
The enzymes the microbe has
And how active the enzymes are
Chemical analyses of end-products are
useful in microbe identification
See Lab experiment 17
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Overview: Fermentation
1. Glycolysis: glucose
 pyruvic acid
1.
2. Ions  pyruvic acid
 form end products
2.
Fig. 5.18a
21
End products of various microbes:
Fig. 5.18b
Single products
Multiple products
Homofermentations
Heterofermentations
22
23
Fermentation Test:
(see lab Ex 17)
Fig. 5.23
a.
b.
c.
d.
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Compare: Aerobic, Anaerobic, Fermentation
25
Q’s
1. Aerobic respiration differs from
anaerobic respiration in which of the
following respects?
a. Aerobic respiration requires the ETS
b. Aerobic respiration gets electrons from the
Krebs cycle
c. Anaerobic respiration is glycolysis
d. The final electron acceptors are different
e. Aerobic respiration produces more ATP
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Q’s
1. Which of the following is NOT an end
product of fermentation?
a.
b.
c.
d.
e.
Lactic acid
Glycerol
Acetone
Pyruvic acid
Ethyl alcohol
2. In fermentation, ATP is generated only
in __________. (name the pathway)
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Q’s
1. Which of the following compounds
has the greatest amount of energy for
a cell?
a. CO2
b. ATP
c. Glucose
d. O2
e. Lactic acid
2. Both fermentation and aerobic
respiration require oxygen.
True
False
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Q’s
1. Biochemical tests for the identification
of bacteria involve testing fermentation
products or amino acid catabolism.
True
False
2. Which of the test
tubes is producing
both acid & gas?
a. b. c. d.
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Q’s
1. Which of the following four stages of
glucose oxidation produces the most
ATP?
a.
b.
c.
d.
Production of acetyl CoA
Krebs cycle
Glycolysis
Oxidative phosphorylation
2. At the completion of aerobic
respiration energy has been formed in
what molecule? ____________
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Q’s
1. The complete oxidation of glucose
typically involves which 3 stages?
a.
b.
c.
d.
Photosynthesis, fermentation & oxidation
Glycolysis, Krebs Cycle & ETS
Catabolism, anabolism & metabolism
Substrate phosphorylation, Calvin cycle &
reduction
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Q’s
1. Which of the following is the best
definition of respiration?
a. A sequence of carrier molecules with an
inorganic molecule as the final electron
acceptor
b. A sequence of carrier molecules with O2 as
the final electron acceptor
c. A method of generating ATP
d. The complete oxidation of glucose to CO2
and H2O
e. A series of reactions in which pyruvic acid is
oxidized to CO2 and H2O
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