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pp. 115-138; 144-148
Microbial MetabolismMicrobial Metabolism5-a5-a
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Chapter 5 OverviewChapter 5 Overview
• Metabolism
• Enzymes
• Common energy pathways used by microbes
– Fermentation– Aerobic respiration– Anaerobic respiration
• Metabolic diversity among organisms
• 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
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Metabolism Metabolism Energy-Balancing Process
Molecule breakdown coupled with molecules synthesized
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Enzymes 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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EnzymesEnzymes
• Provide a structure, a framework
– To allow collisions to occur
– And the chemical reaction to occur
AB A + BAB A + BSubstrate Products
6Fig. 5.2
Energy Requirements - Chemical ReactionEnergy Requirements - Chemical Reaction
The reaction is: AB A + B
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Mechanism of Enzymatic Action:Mechanism of Enzymatic Action:
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
Fig. 5.4a
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• Names usually end in –ase
Naming enzymes:Naming enzymes:
Enzyme classification: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):Enzyme classification (6 classes):
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• Some enzymes consist only of protein
• Most consist of both a protein and a non-protein 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
Enzyme ComponentsEnzyme Components
* p. 119
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• Apoenzymes are inactive by themselves– They must be activated by cofactors
• Apoenzymes + cofactors form a– Holoenzyme
Fig. 5.3
+
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Enzyme & CofactorsEnzyme & Cofactors
NAD+NADP+FMN, FADCoenzyme A
Nicotinamide adenine dinucleotideNicotinamide adenine dinucleotide phosphateFlavin mononucleotide, Flavin adenine dinucleotideImportant in the Krebs cycle
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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.
Fig. 5.4b
• 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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Organisms - Metabolic DiversityOrganisms - Metabolic Diversity
• 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 15
Combine Energy & Carbon
16Fig. 5.27
Nutritional Classification of Organisms
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1. All of the following are enzymes except:
a. Threonine deamainaseb. Acetylc. Peroxidased. Urease
Q’sQ’s
2. Enzymes work most effectively at their optimal temperature and pH.
a. True b. False
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1. Beggiatoa bacteria use carbon dioxide for their carbon source and hydrogen sulfide as an energy source. This organism is a:
a. Photoheterotroph
b. Chemoheterotroph
c. Photoautotroph
d. Chemoautotroph
Q’sQ’s
Hint: Fig. 5.27
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Q’sQ’sIn 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’sQ’s1. 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’sQ’s1. 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’sQ’s1. 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’sQ’s
OrganismCarbon Source
Energy Source
Photoautotroph
Photoheterotroph
Chemoautotroph
Chemoheterotroph
Fill in the blanks:
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