Ch. 5 - Microbial Metabolism: Fundamental Chemical Reactions and Pathways

Microbial Metabolism

Definition and Importance

Microbial metabolism encompasses the collection of controlled biochemical reactions that occur within a microbe. The ultimate function of metabolism is to reproduce the organism, ensuring survival and propagation.

• Metabolism: The sum of all chemical reactions within a cell.

• Biochemical reactions: Controlled processes that transform nutrients into energy and cellular components.

• Reproduction: The end goal of metabolism, allowing microbes to multiply.

Eight Elementary Statements Guiding Metabolic Processes

Microbial metabolic processes follow a logical sequence, ensuring efficient energy use and growth.

• Every cell acquires nutrients necessary for survival.

• Metabolism requires energy from light or catabolism of nutrients.

• Energy is stored in adenosine triphosphate (ATP), the universal energy currency.

• Cells catabolize nutrients to form precursor metabolites.

• Precursor metabolites, ATP energy, and enzymes are used in anabolic reactions.

• Enzymes plus ATP facilitate the formation of macromolecules.

• Cells grow by assembling macromolecules into cellular structures.

• Cells reproduce once they have doubled in size.

Overview of Metabolism

Metabolic Pathways

Metabolism consists of two major classes of reactions: catabolism and anabolism. These pathways are interconnected and essential for cellular function.

• Catabolic pathways:

  • Break larger molecules into smaller products.

  • Exergonic: Release energy.

  • Example: Breakdown of glucose during glycolysis.

• Anabolic pathways:

  • Synthesize large molecules from the smaller products of catabolism.

  • Endergonic: Require more energy than they release.

  • Example: Synthesis of proteins from amino acids.

Energy Flow in Metabolism

Energy is transferred and transformed during metabolic reactions. Catabolism provides energy and precursor molecules for anabolism, while anabolism uses energy to build cellular structures.

• ATP is generated during catabolic reactions and consumed during anabolic reactions.

• Energy is lost as heat during both catabolic and anabolic processes.

• Precursor molecules from catabolism are used to build macromolecules in anabolism.

Diagram: Metabolism Is Composed of Catabolic and Anabolic Reactions

Catabolism (energy release, breakdown of nutrients) → ATP/precursor molecules → Anabolism (energy consumption, synthesis of macromolecules). Energy is lost as heat at each stage. Cellular processes such as growth, division, and structure formation depend on these reactions.

Key Terms and Concepts

• Catabolism: The breakdown of complex molecules into simpler ones, releasing energy.

• Anabolism: The synthesis of complex molecules from simpler ones, requiring energy input.

• Exergonic reaction: A reaction that releases energy.

• Endergonic reaction: A reaction that requires energy input.

• ATP (Adenosine Triphosphate): The primary energy carrier in cells.

Example: ATP Cycle

During catabolism, nutrients such as glucose are broken down, releasing energy that is stored in ATP. During anabolism, ATP is used to power the synthesis of macromolecules like proteins and nucleic acids.

Equations

• ATP formation (catabolism): $\text{ADP} + \text{P}_i + \text{energy} \rightarrow \text{ATP}$

• ATP utilization (anabolism): $\text{ATP} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

Additional info: The overview diagram (Figure 5.1) visually represents the cyclical nature of metabolism, showing the flow from catabolism to anabolism and the role of ATP and precursor molecules in cellular processes.