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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: