Microbial Metabolism: Principles and Pathways

Ch. 5 Microbial Metabolism

Introduction to Microbial Metabolism

Microbial metabolism encompasses all chemical reactions occurring within a microorganism. These reactions are essential for growth, energy production, and cellular maintenance. Metabolism is fundamentally an energy-balancing act, with reactions either releasing or requiring energy.

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

• Reactions are classified based on energy changes: those that release energy and those that require energy.

• Metabolic processes are crucial for microbial survival and adaptation.

Classification of Metabolic Reactions

Metabolism is divided into two major classes based on energy flow:

• Catabolism (Exergonic Reactions): Chemical reactions that release energy by breaking down complex molecules into simpler ones.

• Anabolism (Endergonic Reactions): Chemical reactions that require energy to build complex molecules from simpler ones.

Catabolism – Catabolic/Degradative Reactions

Overview of Catabolic Pathways

Catabolic reactions are degradative processes that break down macromolecules into their component parts, releasing energy in the process. These reactions are typically hydrolytic, meaning they involve the addition of water to break chemical bonds.

• Catabolic Pathways: Break down complex organic compounds into simpler molecules.

• Energy is released and often captured in the form of ATP.

• Hydrolysis: Addition of water to split bonds in macromolecules.

• Catabolic reactions produce more energy than they consume.

• Example: Breakdown of starch into glucose monomers.

Anabolism – Anabolic/Biosynthetic Reactions

Overview of Anabolic Pathways

Anabolic reactions are biosynthetic processes that build up macromolecules by combining simpler molecules, requiring energy input. These reactions are typically dehydration synthesis reactions, where water is removed to form new bonds.

• Anabolic Pathways: Synthesize complex molecules from simpler precursors.

• Energy is consumed to drive these reactions.

• Dehydration synthesis: Removal of water to form bonds between molecules.

• Anabolic reactions consume more energy than they produce.

• Example: Synthesis of proteins from amino acids.

Comparison of Catabolism and Anabolism

Catabolic and anabolic reactions are interconnected, with energy released from catabolism often used to drive anabolic processes.

Process	Energy Flow	Type of Reaction	Example
Catabolism	Releases energy (exergonic)	Hydrolysis	Glucose breakdown
Anabolism	Requires energy (endergonic)	Dehydration synthesis	Protein synthesis

Key Terms:

• Exergonic: Reactions that release energy.

• Endergonic: Reactions that require energy input.

• Hydrolysis: Chemical breakdown involving water.

• Dehydration Synthesis: Formation of larger molecules by removing water.

Additional info: Catabolic and anabolic reactions are often coupled in living cells, with ATP serving as the energy currency that links these processes.