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Chapter 8
Microbial Metabolism: The Chemical Crossroads of Life
Chapter Outline
8.1. The Metabolism of Microbes
A. Metabolism
1. Anabolism
2. Catabolism
3. Metabolism:
a. Assembles smaller molecules into larger macromolecules for the cell
b. Degrades macromolecules into smaller molecules and yields energy
c. Conserves energy in the form of ATP or heat
B. Enzymes: Catalyzing the chemical reactions of life
1. How do enzymes work?
a. Catalysts
b. Energy of activation
c. Substrates
2. Enzyme structure
a. Simple enzymes
b. Conjugated enzymes
c. Holoenzyme
i. Apoenzyme
ii. Cofactors
1. Coenzymes (organic molecules)
2. Inorganic elements (metal ions)
3. Apoenzymes: Specificity and the active site
a. Active site: where the substrate binds
b. Crevice or groove on the enzyme
4. Enzyme-substrate interactions
a. Temporary union between enzyme and substrate
b. Weak, reversible bonding
c. Reaction occurs on substrate
d. Product is formed and released
5. Cofactors: Supporting the work of enzymes
a. Metallic cofactors
b. Coenzymes and vitamins
6. Classification of enzyme functions
a. Location and regularity of enzyme action
i. Exoenzymes
ii. Endoenzymes
iii. Constitutive enzymes
iv. Regulated enzymes
b. Synthesis and hydrolysis reactions
i. Dehydration reactions
ii. Hydrolysis reaction
c. Transfer reactions by enzymes
i. Oxidation and reduction
ii. Aminotransferases
iii. Phosphotransferases
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iv. Methyltransferases
v. Decarboxylases
7. The role of microbial enzymes in disease
a. Streptokinase: Streptococcus pyogenes
b. Elastase and collagenase: Pseudomonas aeruginosa
c. Lecithinase C: Clostridium perfringens
8. The sensitivity of enzymes to their environments
a. Labile
b. Denaturation
C. Regulation of enzymatic activity and metabolic pathways
1. Metabolic pathways
a. Multistep series of reactions
b. Interconnected and merge at many sites
2. Direct controls on the actions of enzymes
a. Competitive inhibition
b. Noncompetitive inhibition through negative feedback
3. Controls on enzyme synthesis
a. Enzyme repression
b. Enzyme induction: Escherichia coli
8.2. The Pursuit and Utilization of Energy
A. Energy in cells
1. Exergonic
2. Endergonic
B. A closer look at biological oxidation and reduction
1. Redox reactions
a. Redox pair: electron donor and electron acceptor
2. Phosphorylation and ATP synthesis
3. Electron transfer
4. Dehydrogenation
5. Electron carriers: Molecular shuttles
a. NAD and NADH
b. Final electron acceptor in aerobic metabolism is oxygen
c. In anaerobic metabolism, final electron acceptor is some other organic or
inorganic compound.
C. Adenosine triphosphate: Metabolic money
1. The molecular structure of ATP
a. Phosphate, sugar (ribose), and a base (adenine)
2. The metabolic role of ATP
a. Substrate-level phosphorylation
b. Oxidative phosphorylation
c. Photophosphorylation
8.3. The Pathways
A. Introduction
1. Metabolism
a. Enzymes
b. Catabolize
c. Precursor molecules
d. Anabolize
e. Reducing power
f. Energy
B. Catabolism: Getting materials and energy
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C.
D.
E.
F.
1. Glycolysis
2. Aerobic respiration
a. Glycolysis
b. Krebs cycle
c. Respiratory chain
3. Anaerobic respiration
a. Glycolysis
b. Final electron acceptor is not oxygen
Aerobic respiration
1. Glucose: The starting compound
2. Glycolysis: The starting lineup
i. An anaerobic step
ii. Pyruvic acid synthesis
iii. Steps in the glycolytic pathway
b. Pyruvic acid: A central metabolite
c. The Krebs cycle: A carbon and energy wheel
i. The processing of pyruvic acid
ii. Role of acetyl coenzyme A
iii. Role of NADH
iv. Steps in the Krebs cycle
3. The respiratory chain: Electron transport and oxidative phosphorylation
a. Elements of electron transport: The energy cascade
i. ATP synthase
ii. Oxidative phosphorylation
b. Formation of ATP and chemiosmosis
c. Potential yield of ATPs from oxidative phosphorylation
4. Summary of aerobic respiration
a. Total possible yield
b. The terminal step
i. Formation of water
ii. Neisseria, Pseudomonas, Bacillus
iii. Klebsiella, Enterobacter
iv. Streptococcus
v. Superoxide dismutase and catalase
Anaerobic respiration
1. Nitrate and nitrite reduction systems
a. E. coli
2. Denitrification
a. Pseudomonas and Bacillus
Fermentation
1. Products of fermentation in microorganisms
a. Alcoholic fermentation
i. Converting pyruvic acid to ethanol
b. Acidic fermentation
i. Streptococcus and Lactobacillus: Homolactic fermentation
ii. Leuconostoc: Heterolactic fermentation
c. Mixed acid fermentation
i. Propionibacterium
Catabolism of noncarbohydrate compounds
1. Lipid catabolism:
a. Lipases: break down lipids to fatty acids and glycerol
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b. Fatty acids are broken down through beta oxidation
2. Protein catabolism:
a. Proteases
b. Deamination
8.4. Biosynthesis and the Crossing Pathways of Metabolism
A. The frugality of the cell: Waste not, want not
1. Amphibolic sources of cellular building blocks
a. Gluconeogenesis
b. Beta-oxidation
c. Amination
d. Transamination
B. Anabolism: Formation of macromolecules
1. Carbohydrate biosynthesis
2. Amino acids, protein synthesis, and nucleic acid synthesis
C. Assembly of the cell
8.5 It All Starts with the Sun
A. Photosynthesis
1. Two phases
a. Light-dependent reactions require sunlight
b. Light-independent reactions proceed in light or dark conditions
c. Photons are energy packets from the sun
d. Photosynthetic pigments absorb energy:
i. Chlorophylls
ii. Carotenoids
iii. Phycobilins
2. Light-dependent reactions
a. Take place in the thylakoid membranes (grana) of the chloroplast
b. Photosystem I
c. Photosystem II
i. Photolysis
ii. Cytochromes
3. Light-independent reactions
a. RuBP
b. Carbon fixation
4. Other mechanisms of photosynthesis
a. Oxygenic
b. Anoxygenic
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