5-a
Microbial Metabolism
pp. 115-138; 144-148
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Chapter 5 Overview
• Metabolism
• Enzymes
• Common energy pathways used by
microbes
– Fermentation
– Aerobic respiration
– Anaerobic respiration
• Metabolic diversity among organisms
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Metabolism
Energy-Balancing Process
• Release energy
– Catabolism
– Breakdown of
molecules
• Sugar  CO2 + H20
– Provides ‘building
blocks’ for anabolism
– Provides energy for
anabolism
• ATP  ADP + energy
• Requires energy
– Anabolism
– Synthesis of
molecules
• Amino acids  protein
– Provides molecules for
catabolism
– Provides ATP for
catabolism
• ADP + energy  ATP
Molecule breakdown coupled with molecules synthesized
3
Enzymes
…Enable Energy-Balancing Process
•
•
•
•
•
•
•
Are a catalyst = speed up reaction
Increase the reaction rate
Lower the energy of activation
Are not altered in the reaction
Are highly specific
Each acts on a specific substance, the substrate
Each catalyzes only one reaction
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Enzymes
• Provide a structure, a framework
– To allow collisions to occur
– And the chemical reaction to occur
AB  A + B
Substrate
Products
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Energy Requirements - Chemical Reaction
The reaction is: AB  A + B
Fig. 5.2
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Mechanism of Enzymatic Action:
Fig. 5.4a
When an enzyme and substrate combine:
– The substrate is transformed, to products
– And the enzyme is recovered, unaltered
Turnover number ~ 1-10,000 molecules per second
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Naming enzymes:
• Names usually end in –ase
Enzyme classification:
• Based on the type of chemical reaction they
catalyze
– Example: oxidoreductases (ox-redox rxns)
• Within each class, named for the specific
reaction
– If remove hydrogen, called dehydrogenases
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Enzyme classification (6 classes):
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Enzyme Components
• Some enzymes consist only of protein
• Most consist of both a protein and a nonprotein component
– The protein called an apoenzyme
– The non-protein part called a cofactor
• Cofactors are
– Ions of iron, zinc, magnesium, calcium etc*
– If a cofactor is an organic molecule, it is called a:
• Coenzyme
* p. 119
10
• Apoenzymes are inactive by themselves
– They must be activated by cofactors
• Apoenzymes + cofactors form a
– Holoenzyme
+
Fig. 5.3
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Enzyme & Cofactors
NAD+
NADP+
FMN, FAD
Coenzyme A
Nicotinamide adenine dinucleotide
Nicotinamide adenine dinucleotide phosphate
Flavin mononucleotide, Flavin adenine dinucleotide
Important in the Krebs cycle
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Fig. 5.4b
Enzymes are characterized by specificity
– Specificity is a function of their active sites
(see ‘groove’)
– Enzyme + substrate = slight shape change
* Animation: Enzyme–Substrate Interactions. The Microbiology Place.
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Organisms - Metabolic Diversity
• Chemotrophs
– Oxidation-reduction reactions of organic or
inorganic compounds for energy
• Phototrophs
– Use light as primary source of energy
• Autotrophs
– Use CO2 for principal carbon source
• Heterotrophs
– Use organic carbon source
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Combine Energy & Carbon
• Photoautotrophs
– Energy = light; carbon = CO2
• Photoheterotrophs
– Energy = light; carbon = organic source
• Chemoautotrophs
– Energy = organic or inorganic compounds;
carbon = CO2
• Chemoheterotrophs*
– Energy = organic or inorganic compounds;
carbon = organic source
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Nutritional Classification of Organisms
Fig. 5.27
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Q’s
1. All of the following are enzymes
except:
a.
b.
c.
d.
Threonine deamainase
Acetyl
Peroxidase
Urease
2. Enzymes work most effectively at
their optimal temperature and pH.
a. True
b. False
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Q’s
1. Beggiatoa bacteria use carbon
dioxide for their carbon source and
hydrogen sulfide as an energy source.
This organism is a:
a.
b.
c.
d.
Photoheterotroph
Chemoheterotroph
Photoautotroph
Chemoautotroph
Hint: Fig. 5.27
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Q’s
In the figure shown, what is the small
organic molecule called that is needed to
activate the apoenzyme?
A. Holoenzyme B. Enzyme C. Coenzyme
D. Substrate E. Reactant
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Q’s
1. A dehydrogenase is an example of a/an
_____________?
2. Nitrobacter bacteria use CO2 for their
carbon source and nitrate ions as an
energy source. This organism is a:
A. Chemoautotroph
B. Chemoheterotroph
C. Photoheterotroph
D. Photoautotroph
Hint: Fig. 5.27
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Q’s
1. A coenzyme assists an enzyme by
accepting or donating matter. What does
NAD+ transfer?
A. CoA
B. Electrons
C. Acetyl groups
D. ATP
Hint: Table 5.2
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Q’s
1. Organisms that use carbon dioxide as a
carbon source and energy sources such
as ammonia or hydrogen sulfide are
called:
A. Photoautotrophs
B. Photoheterotrophs
C. Chemoheterotrophs
D. Chemoautotrophs
Hint: Fig. 5.27
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Q’s
Fill in the blanks:
Organism
Carbon
Source
Energy
Source
Photoautotroph
Photoheterotroph
Chemoautotroph
Chemoheterotroph
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