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Chapter 7
Microbial Metabolism
Metabolism is the sum of cellular chemical and physical activities. It consists of
anabolism, synthetic reactions that convert small molecules into large molecules, and
catabolism, in which large molecules are degraded and energy is produced. Metabolism
is made possible by organic catalysts, or enzymes, that speed up reactions to rates
compatible with biological processes. Enzymes are not consumed and can be reused.
Each enzyme acts specifically upon its matching molecule or substrate. Enzymes are
labile (unstable) and function only within narrow operating ranges of temperature,
osmotic pressure, and pH, and they are especially vulnerable to denaturation. Enzymes
are frequently the targets for physical and chemical agents used in control of microbes.
Energy is the capacity of a system to perform work. It is consumed in endergonic
reactions and is released in exergonic reactions. Extracting energy requires a series of
electron carriers arrayed in a redox chain between electron donors and electron
acceptors.
Carbohydrates, such as glucose, are energy-rich because when catabolized they can
yield a large number of electrons per molecule. Glycolysis is a pathway that degrades
glucose to pyruvic acid without requiring oxygen. Pyruvic acid is processed in aerobic
respiration via the Krebs cycle and its associated electron transport chain. Pyruvic acid
undergoes further oxidation and decarboxylation in the Krebs cycle, which generates
ATP, CO2, and large amounts of reduced carriers (NADH and FADH2).The respiratory
chain then completes energy extraction and the final electron acceptor in aerobic
respiration is oxygen.
In anaerobic respiration, compounds such as sulfate, nitrate, or nitrite serve this
function. Fermentation is anaerobic respiration in which both the electron donor and
final electron acceptors are organic compounds. Production of alcohol, vinegar, and
certain industrial solvents relies upon fermentation.
Glycolysis and the Krebs cycle are central pathways that link catabolic and anabolic
pathways, allowing cells to break down different classes of molecules in order to
synthesize compounds required by the cell.
Metabolism and the Role of Enzymes
1. Describe the relationship among metabolism, catabolism, and anabolism.
2. Fully define the structure and function of enzymes.
3. Differentiate between constitutive and regulated enzymes.
4. Diagram some different patterns of metabolism.
5. Describe how enzymes are controlled.
The Pursuit and Utilization of Energy
6. Name the chemical in which energy is stored in cells.
7. Create a general diagram of a redox reaction.
8. Identify electron carriers used by cells.
Catabolism
9. Name three basic catabolic pathways, and give an estimate of how much ATP each
of them yields.
10. Write a summary statement describing glycolysis.
11. Describe the Krebs cycle.
12. Discuss the significance of the electron transport system.
13. Point out how anaerobic respiration differs from aerobic respiration.
14. Provide a summary of fermentation.
15. Describe how noncarbohydrate compounds are catabolized.
Anabolism and the Crossing Pathways of Metabolism
16. Provide an overview of the anabolic stages of metabolism.
17. Define amphibolism.
Key Terms and Phrases
Anabolism
Catabolism
Metabolism
Enzymes
Catalysts
Substrate
Holoenzyme
Apoenzyme
Cofactors
Active site
Coenzymes
Vitamins
Constitutive enzymes
Oxidized
Reduced
Labile
Denaturation
Competitive inhibition
Catalytic site
Substrate
Enzyme repression
Enzyme induction
Endergonic
Exergonic
Denitritification
Phosphorylate
Lipases
Final electron acceptor
Proteases
FAD
ATP
Glycolysis
Krebs Cycle
Aerobic respiration
Ferment
Anaerobic respiration
Pyruvic acid
Electron transport
Fermentation
Amphibolism
Deanimation
ATP Synthase
Oxidative phosphorylation
Cytochromes
Amination
Beta oxidation
Non-competitive inhibiton